refactor(web): extract asset grid layout logic into AssetLayout component

- Extracts the asset grid rendering logic from `MonthSegment` into a
  dedicated `AssetLayout` component
- Simplifies `MonthSegment` by delegating layout responsibilities
  while maintaining all existing functionality
- Renames `customLayout` prop to `customThumbnailLayout` for clarity
  across Timeline components


## Changes
  - Created new `AssetLayout.svelte` component that handles:
    - Asset grid rendering with proper positioning
    - Animation transitions
    - Filtering of intersecting viewer assets
  - Updated `MonthSegment.svelte` to use `AssetLayout` via composition
  pattern
  - Renamed `customLayout` to `customThumbnailLayout` in Timeline and
  related components
  - Moved thumbnail click and selection logic to Timeline parent
  component using snippets

server/src/services/notification.service.ts

@@ -161,7 +161,24 @@ export class NotificationService extends BaseService {
 
     const [asset] = await this.assetRepository.getByIdsWithAllRelationsButStacks([assetId]);
     if (asset) {
-      this.eventRepository.clientSend('on_asset_update', userId, mapAsset(asset));
+      // need to specify authDto to this mapAsset request, because it tries to prevent
+      // leaking information PR#7580 which expects a userId in the auth options object
+      this.eventRepository.clientSend(
+        'on_asset_update',
+        userId,
+        mapAsset(asset, {
+          auth: {
+            user: {
+              id: userId,
+              isAdmin: false,
+              name: '',
+              email: '',
+              quotaUsageInBytes: 0,
+              quotaSizeInBytes: null,
+            },
+          },
+        }),
+      );
     }
   }
 

web/src/lib/components/timeline/AssetLayout.svelte

@@ -0,0 +1,68 @@
+<script lang="ts">
+  import { uploadAssetsStore } from '$lib/stores/upload';
+
+  import { flip } from 'svelte/animate';
+  import { scale } from 'svelte/transition';
+
+  import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
+  import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
+  import type { ViewerAsset } from '$lib/managers/timeline-manager/viewer-asset.svelte';
+  import type { CommonPosition } from '$lib/utils/layout-utils';
+  import type { Snippet } from 'svelte';
+
+  let { isUploading } = uploadAssetsStore;
+
+  interface Props {
+    viewerAssets: ViewerAsset[];
+    width: number;
+    height: number;
+    photostreamManager: PhotostreamManager;
+    thumbnail: Snippet<
+      [
+        {
+          asset: TimelineAsset;
+          position: CommonPosition;
+        },
+      ]
+    >;
+    customThumbnailLayout?: Snippet<[asset: TimelineAsset]>;
+  }
+
+  let { viewerAssets, width, height, photostreamManager, thumbnail, customThumbnailLayout }: Props = $props();
+
+  const transitionDuration = $derived.by(() => (photostreamManager.suspendTransitions && !$isUploading ? 0 : 150));
+  const scaleDuration = $derived(transitionDuration === 0 ? 0 : transitionDuration + 100);
+
+  function filterIntersecting<R extends { intersecting: boolean }>(intersectables: R[]) {
+    return intersectables.filter((intersectable) => intersectable.intersecting);
+  }
+</script>
+
+<!-- Image grid -->
+<div data-image-grid class="relative overflow-clip" style:height={height + 'px'} style:width={width + 'px'}>
+  {#each filterIntersecting(viewerAssets) as viewerAsset (viewerAsset.id)}
+    {@const position = viewerAsset.position!}
+    {@const asset = viewerAsset.asset!}
+
+    <!-- note: don't remove data-asset-id - its used by web e2e tests -->
+    <div
+      data-asset-id={asset.id}
+      class="absolute"
+      style:top={position.top + 'px'}
+      style:left={position.left + 'px'}
+      style:width={position.width + 'px'}
+      style:height={position.height + 'px'}
+      out:scale|global={{ start: 0.1, duration: scaleDuration }}
+      animate:flip={{ duration: transitionDuration }}
+    >
+      {@render thumbnail({ asset, position })}
+      {@render customThumbnailLayout?.(asset)}
+    </div>
+  {/each}
+</div>
+
+<style>
+  [data-image-grid] {
+    user-select: none;
+  }
+</style>

web/src/lib/components/timeline/MonthSegment.svelte

@@ -0,0 +1,109 @@
+<script lang="ts">
+  import type { MonthGroup } from '$lib/managers/timeline-manager/month-group.svelte';
+  import type { TimelineManager } from '$lib/managers/timeline-manager/timeline-manager.svelte';
+  import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
+  import { assetsSnapshot } from '$lib/managers/timeline-manager/utils.svelte';
+  import { uploadAssetsStore } from '$lib/stores/upload';
+  import { Icon } from '@immich/ui';
+  import { mdiCheckCircle, mdiCircleOutline } from '@mdi/js';
+
+  import AssetLayout from '$lib/components/timeline/AssetLayout.svelte';
+  import { DayGroup } from '$lib/managers/timeline-manager/day-group.svelte';
+  import type { AssetInteraction } from '$lib/stores/asset-interaction.svelte';
+  import type { CommonPosition } from '$lib/utils/layout-utils';
+  import type { Snippet } from 'svelte';
+  let { isUploading } = uploadAssetsStore;
+  interface Props {
+    thumbnail: Snippet<[{ asset: TimelineAsset; position: CommonPosition; dayGroup: DayGroup; groupIndex: number }]>;
+    customThumbnailLayout?: Snippet<[TimelineAsset]>;
+    singleSelect: boolean;
+    assetInteraction: AssetInteraction;
+    monthGroup: MonthGroup;
+    timelineManager: TimelineManager;
+    onDayGroupSelect: (daygroup: DayGroup, assets: TimelineAsset[]) => void;
+  }
+  let {
+    thumbnail: thumbnailWithGroup,
+    customThumbnailLayout,
+    singleSelect,
+    assetInteraction,
+    monthGroup,
+    timelineManager,
+    onDayGroupSelect,
+  }: Props = $props();
+  let isMouseOverGroup = $state(false);
+  let hoveredDayGroup = $state();
+  const transitionDuration = $derived.by(() =>
+    monthGroup.timelineManager.suspendTransitions && !$isUploading ? 0 : 150,
+  );
+  function filterIntersecting<R extends { intersecting: boolean }>(intersectables: R[]) {
+    return intersectables.filter((intersectable) => intersectable.intersecting);
+  }
+</script>
+
+{#each filterIntersecting(monthGroup.dayGroups) as dayGroup, groupIndex (dayGroup.day)}
+  {@const absoluteWidth = dayGroup.left}
+  {@const isDayGroupSelected = assetInteraction.selectedGroup.has(dayGroup.groupTitle)}
+  <!-- svelte-ignore a11y_no_static_element_interactions -->
+  <section
+    class={[
+      { 'transition-all': !monthGroup.timelineManager.suspendTransitions },
+      !monthGroup.timelineManager.suspendTransitions && `delay-${transitionDuration}`,
+    ]}
+    data-group
+    style:position="absolute"
+    style:transform={`translate3d(${absoluteWidth}px,${dayGroup.top}px,0)`}
+    onmouseenter={() => {
+      isMouseOverGroup = true;
+      hoveredDayGroup = dayGroup.groupTitle;
+    }}
+    onmouseleave={() => {
+      isMouseOverGroup = false;
+      hoveredDayGroup = null;
+    }}
+  >
+    <!-- Date group title -->
+    <div
+      class="flex pt-7 pb-5 max-md:pt-5 max-md:pb-3 h-6 place-items-center text-xs font-medium text-immich-fg dark:text-immich-dark-fg md:text-sm"
+      style:width={dayGroup.width + 'px'}
+    >
+      {#if !singleSelect}
+        <div
+          class="hover:cursor-pointer transition-all duration-200 ease-out overflow-hidden w-0"
+          class:w-8={(hoveredDayGroup === dayGroup.groupTitle && isMouseOverGroup) ||
+            assetInteraction.selectedGroup.has(dayGroup.groupTitle)}
+          onclick={() => onDayGroupSelect(dayGroup, assetsSnapshot(dayGroup.getAssets()))}
+          onkeydown={() => onDayGroupSelect(dayGroup, assetsSnapshot(dayGroup.getAssets()))}
+        >
+          {#if isDayGroupSelected}
+            <Icon icon={mdiCheckCircle} size="24" class="text-primary" />
+          {:else}
+            <Icon icon={mdiCircleOutline} size="24" color="#757575" />
+          {/if}
+        </div>
+      {/if}
+
+      <span class="w-full truncate first-letter:capitalize" title={dayGroup.groupTitleFull}>
+        {dayGroup.groupTitle}
+      </span>
+    </div>
+
+    <AssetLayout
+      photostreamManager={timelineManager}
+      viewerAssets={dayGroup.viewerAssets}
+      height={dayGroup.height}
+      width={dayGroup.width}
+      {customThumbnailLayout}
+    >
+      {#snippet thumbnail({ asset, position })}
+        {@render thumbnailWithGroup({ asset, position, dayGroup, groupIndex })}
+      {/snippet}
+    </AssetLayout>
+  </section>
+{/each}
+
+<style>
+  section {
+    contain: layout paint style;
+  }
+</style>

web/src/lib/components/timeline/Timeline.svelte

@@ -2,14 +2,15 @@
   import { afterNavigate, beforeNavigate } from '$app/navigation';
   import { page } from '$app/stores';
   import { resizeObserver, type OnResizeCallback } from '$lib/actions/resize-observer';
-  import type { Action } from '$lib/components/asset-viewer/actions/action';
+  import Thumbnail from '$lib/components/assets/thumbnail/thumbnail.svelte';
+  import MonthSegment from '$lib/components/timeline/MonthSegment.svelte';
   import Scrubber from '$lib/components/timeline/Scrubber.svelte';
+  import TimelineAssetViewer from '$lib/components/timeline/TimelineAssetViewer.svelte';
   import TimelineKeyboardActions from '$lib/components/timeline/actions/TimelineKeyboardActions.svelte';
   import { AssetAction } from '$lib/constants';
   import HotModuleReload from '$lib/elements/HotModuleReload.svelte';
   import Portal from '$lib/elements/Portal.svelte';
   import Skeleton from '$lib/elements/Skeleton.svelte';
-  import { authManager } from '$lib/managers/auth-manager.svelte';
   import type { DayGroup } from '$lib/managers/timeline-manager/day-group.svelte';
   import type { MonthGroup } from '$lib/managers/timeline-manager/month-group.svelte';
   import { TimelineManager } from '$lib/managers/timeline-manager/timeline-manager.svelte';
@@ -19,14 +20,17 @@
   import { assetViewingStore } from '$lib/stores/asset-viewing.store';
   import { isSelectingAllAssets } from '$lib/stores/assets-store.svelte';
   import { mobileDevice } from '$lib/stores/mobile-device.svelte';
-  import { updateStackedAssetInTimeline, updateUnstackedAssetInTimeline } from '$lib/utils/actions';
   import { navigate } from '$lib/utils/navigation';
-  import { getTimes, toTimelineAsset, type ScrubberListener, type TimelineYearMonth } from '$lib/utils/timeline-util';
-  import { getAssetInfo, type AlbumResponseDto, type PersonResponseDto } from '@immich/sdk';
+  import {
+    getSegmentIdentifier,
+    getTimes,
+    type ScrubberListener,
+    type TimelineYearMonth,
+  } from '$lib/utils/timeline-util';
+  import { type AlbumResponseDto, type PersonResponseDto } from '@immich/sdk';
   import { DateTime } from 'luxon';
   import { onMount, type Snippet } from 'svelte';
   import type { UpdatePayload } from 'vite';
-  import TimelineDateGroup from './TimelineDateGroup.svelte';
 
   interface Props {
     isSelectionMode?: boolean;
@@ -54,7 +58,7 @@
     onEscape?: () => void;
     children?: Snippet;
     empty?: Snippet;
-    customLayout?: Snippet<[TimelineAsset]>;
+    customThumbnailLayout?: Snippet<[TimelineAsset]>;
     onThumbnailClick?: (
       asset: TimelineAsset,
       timelineManager: TimelineManager,
@@ -85,11 +89,11 @@
     onEscape = () => {},
     children,
     empty,
-    customLayout,
+    customThumbnailLayout,
     onThumbnailClick,
   }: Props = $props();
 
-  let { isViewing: showAssetViewer, asset: viewingAsset, preloadAssets, gridScrollTarget, mutex } = assetViewingStore;
+  let { isViewing: showAssetViewer, asset: viewingAsset, gridScrollTarget } = assetViewingStore;
 
   let element: HTMLElement | undefined = $state();
 
@@ -392,126 +396,6 @@
     }
   };
 
-  const handlePrevious = async () => {
-    const release = await mutex.acquire();
-    const laterAsset = await timelineManager.getLaterAsset($viewingAsset);
-
-    if (laterAsset) {
-      const preloadAsset = await timelineManager.getLaterAsset(laterAsset);
-      const asset = await getAssetInfo({ ...authManager.params, id: laterAsset.id });
-      assetViewingStore.setAsset(asset, preloadAsset ? [preloadAsset] : []);
-      await navigate({ targetRoute: 'current', assetId: laterAsset.id });
-    }
-
-    release();
-    return !!laterAsset;
-  };
-
-  const handleNext = async () => {
-    const release = await mutex.acquire();
-    const earlierAsset = await timelineManager.getEarlierAsset($viewingAsset);
-
-    if (earlierAsset) {
-      const preloadAsset = await timelineManager.getEarlierAsset(earlierAsset);
-      const asset = await getAssetInfo({ ...authManager.params, id: earlierAsset.id });
-      assetViewingStore.setAsset(asset, preloadAsset ? [preloadAsset] : []);
-      await navigate({ targetRoute: 'current', assetId: earlierAsset.id });
-    }
-
-    release();
-    return !!earlierAsset;
-  };
-
-  const handleRandom = async () => {
-    const randomAsset = await timelineManager.getRandomAsset();
-
-    if (randomAsset) {
-      const asset = await getAssetInfo({ ...authManager.params, id: randomAsset.id });
-      assetViewingStore.setAsset(asset);
-      await navigate({ targetRoute: 'current', assetId: randomAsset.id });
-      return asset;
-    }
-  };
-
-  const handleClose = async (asset: { id: string }) => {
-    assetViewingStore.showAssetViewer(false);
-    showSkeleton = true;
-    $gridScrollTarget = { at: asset.id };
-    await navigate({ targetRoute: 'current', assetId: null, assetGridRouteSearchParams: $gridScrollTarget });
-  };
-
-  const handlePreAction = async (action: Action) => {
-    switch (action.type) {
-      case removeAction:
-      case AssetAction.TRASH:
-      case AssetAction.RESTORE:
-      case AssetAction.DELETE:
-      case AssetAction.ARCHIVE:
-      case AssetAction.SET_VISIBILITY_LOCKED:
-      case AssetAction.SET_VISIBILITY_TIMELINE: {
-        // find the next asset to show or close the viewer
-        // eslint-disable-next-line @typescript-eslint/no-unused-expressions
-        (await handleNext()) || (await handlePrevious()) || (await handleClose(action.asset));
-
-        // delete after find the next one
-        timelineManager.removeAssets([action.asset.id]);
-        break;
-      }
-    }
-  };
-  const handleAction = (action: Action) => {
-    switch (action.type) {
-      case AssetAction.ARCHIVE:
-      case AssetAction.UNARCHIVE:
-      case AssetAction.FAVORITE:
-      case AssetAction.UNFAVORITE: {
-        timelineManager.updateAssets([action.asset]);
-        break;
-      }
-
-      case AssetAction.ADD: {
-        timelineManager.addAssets([action.asset]);
-        break;
-      }
-
-      case AssetAction.UNSTACK: {
-        updateUnstackedAssetInTimeline(timelineManager, action.assets);
-        break;
-      }
-      case AssetAction.REMOVE_ASSET_FROM_STACK: {
-        timelineManager.addAssets([toTimelineAsset(action.asset)]);
-        if (action.stack) {
-          //Have to unstack then restack assets in timeline in order to update the stack count in the timeline.
-          updateUnstackedAssetInTimeline(
-            timelineManager,
-            action.stack.assets.map((asset) => toTimelineAsset(asset)),
-          );
-          updateStackedAssetInTimeline(timelineManager, {
-            stack: action.stack,
-            toDeleteIds: action.stack.assets
-              .filter((asset) => asset.id !== action.stack?.primaryAssetId)
-              .map((asset) => asset.id),
-          });
-        }
-        break;
-      }
-      case AssetAction.SET_STACK_PRIMARY_ASSET: {
-        //Have to unstack then restack assets in timeline in order for the currently removed new primary asset to be made visible.
-        updateUnstackedAssetInTimeline(
-          timelineManager,
-          action.stack.assets.map((asset) => toTimelineAsset(asset)),
-        );
-        updateStackedAssetInTimeline(timelineManager, {
-          stack: action.stack,
-          toDeleteIds: action.stack.assets
-            .filter((asset) => asset.id !== action.stack.primaryAssetId)
-            .map((asset) => asset.id),
-        });
-        break;
-      }
-    }
-  };
-
   let lastAssetMouseEvent: TimelineAsset | null = $state(null);
 
   let shiftKeyIsDown = $state(false);
@@ -536,7 +420,8 @@
     lastAssetMouseEvent = asset;
   };
 
-  const handleGroupSelect = (timelineManager: TimelineManager, group: string, assets: TimelineAsset[]) => {
+  const handleGroupSelect = (dayGroup: DayGroup, assets: TimelineAsset[]) => {
+    const group = dayGroup.groupTitle;
     if (assetInteraction.selectedGroup.has(group)) {
       assetInteraction.removeGroupFromMultiselectGroup(group);
       for (const asset of assets) {
@@ -556,7 +441,7 @@
     }
   };
 
-  const handleSelectAssets = async (asset: TimelineAsset) => {
+  const onSelectAssets = async (asset: TimelineAsset) => {
     if (!asset) {
       return;
     }
@@ -600,7 +485,7 @@
           break;
         }
         if (started) {
-          await timelineManager.loadMonthGroup(monthGroup.yearMonth);
+          await timelineManager.loadSegment(monthGroup.identifier);
           for (const asset of monthGroup.assetsIterator()) {
             if (deselect) {
               assetInteraction.removeAssetFromMultiselectGroup(asset.id);
@@ -675,9 +560,49 @@
   $effect(() => {
     if ($showAssetViewer) {
       const { localDateTime } = getTimes($viewingAsset.fileCreatedAt, DateTime.local().offset / 60);
-      void timelineManager.loadMonthGroup({ year: localDateTime.year, month: localDateTime.month });
+      void timelineManager.loadSegment(getSegmentIdentifier({ year: localDateTime.year, month: localDateTime.month }));
     }
   });
+
+  const assetSelectHandler = (
+    timelineManager: TimelineManager,
+    asset: TimelineAsset,
+    assetsInDayGroup: TimelineAsset[],
+    groupTitle: string,
+  ) => {
+    void onSelectAssets(asset);
+
+    // Check if all assets are selected in a group to toggle the group selection's icon
+    let selectedAssetsInGroupCount = assetsInDayGroup.filter((asset) =>
+      assetInteraction.hasSelectedAsset(asset.id),
+    ).length;
+
+    // if all assets are selected in a group, add the group to selected group
+    if (selectedAssetsInGroupCount == assetsInDayGroup.length) {
+      assetInteraction.addGroupToMultiselectGroup(groupTitle);
+    } else {
+      assetInteraction.removeGroupFromMultiselectGroup(groupTitle);
+    }
+
+    if (timelineManager.assetCount == assetInteraction.selectedAssets.length) {
+      isSelectingAllAssets.set(true);
+    } else {
+      isSelectingAllAssets.set(false);
+    }
+  };
+
+  const _onClick = (
+    timelineManager: TimelineManager,
+    assets: TimelineAsset[],
+    groupTitle: string,
+    asset: TimelineAsset,
+  ) => {
+    if (isSelectionMode || assetInteraction.selectionActive) {
+      assetSelectHandler(timelineManager, asset, assets, groupTitle);
+      return;
+    }
+    void navigate({ targetRoute: 'current', assetId: asset.id });
+  };
 </script>
 
 <svelte:document onkeydown={onKeyDown} onkeyup={onKeyUp} />
@@ -777,21 +702,47 @@
           style:transform={`translate3d(0,${absoluteHeight}px,0)`}
           style:width="100%"
         >
-          <TimelineDateGroup
-            {withStacked}
-            {showArchiveIcon}
+          <MonthSegment
             {assetInteraction}
-            {timelineManager}
-            {isSelectionMode}
+            {customThumbnailLayout}
             {singleSelect}
             {monthGroup}
-            onSelect={({ title, assets }) => handleGroupSelect(timelineManager, title, assets)}
-            onSelectAssetCandidates={handleSelectAssetCandidates}
-            onSelectAssets={handleSelectAssets}
-            onScrollCompensation={handleScrollCompensation}
-            {customLayout}
-            {onThumbnailClick}
-          />
+            {timelineManager}
+            onDayGroupSelect={handleGroupSelect}
+          >
+            {#snippet thumbnail({ asset, position, dayGroup, groupIndex })}
+              {@const isAssetSelectionCandidate = assetInteraction.hasSelectionCandidate(asset.id)}
+              {@const isAssetSelected =
+                assetInteraction.hasSelectedAsset(asset.id) || timelineManager.albumAssets.has(asset.id)}
+              {@const isAssetDisabled = timelineManager.albumAssets.has(asset.id)}
+              <Thumbnail
+                showStackedIcon={withStacked}
+                {showArchiveIcon}
+                {asset}
+                {groupIndex}
+                onClick={(asset) => {
+                  if (typeof onThumbnailClick === 'function') {
+                    onThumbnailClick(asset, timelineManager, dayGroup, _onClick);
+                  } else {
+                    _onClick(timelineManager, dayGroup.getAssets(), dayGroup.groupTitle, asset);
+                  }
+                }}
+                onSelect={() => {
+                  if (isSelectionMode || assetInteraction.selectionActive) {
+                    assetSelectHandler(timelineManager, asset, dayGroup.getAssets(), dayGroup.groupTitle);
+                    return;
+                  }
+                  void onSelectAssets(asset);
+                }}
+                onMouseEvent={() => handleSelectAssetCandidates(asset)}
+                selected={isAssetSelected}
+                selectionCandidate={isAssetSelectionCandidate}
+                disabled={isAssetDisabled}
+                thumbnailWidth={position.width}
+                thumbnailHeight={position.height}
+              />
+            {/snippet}
+          </MonthSegment>
         </div>
       {/if}
     {/each}
@@ -808,22 +759,7 @@
 
 <Portal target="body">
   {#if $showAssetViewer}
-    {#await import('../asset-viewer/asset-viewer.svelte') then { default: AssetViewer }}
-      <AssetViewer
-        {withStacked}
-        asset={$viewingAsset}
-        preloadAssets={$preloadAssets}
-        {isShared}
-        {album}
-        {person}
-        preAction={handlePreAction}
-        onAction={handleAction}
-        onPrevious={handlePrevious}
-        onNext={handleNext}
-        onRandom={handleRandom}
-        onClose={handleClose}
-      />
-    {/await}
+    <TimelineAssetViewer bind:showSkeleton {timelineManager} {removeAction} {withStacked} {isShared} {album} {person} />
   {/if}
 </Portal>
 

web/src/lib/components/timeline/TimelineAssetViewer.svelte

@@ -0,0 +1,177 @@
+<script lang="ts">
+  import type { Action } from '$lib/components/asset-viewer/actions/action';
+  import { AssetAction } from '$lib/constants';
+  import { authManager } from '$lib/managers/auth-manager.svelte';
+  import { TimelineManager } from '$lib/managers/timeline-manager/timeline-manager.svelte';
+  import { assetViewingStore } from '$lib/stores/asset-viewing.store';
+  import { updateStackedAssetInTimeline, updateUnstackedAssetInTimeline } from '$lib/utils/actions';
+  import { navigate } from '$lib/utils/navigation';
+  import { toTimelineAsset } from '$lib/utils/timeline-util';
+  import { getAssetInfo, type AlbumResponseDto, type PersonResponseDto } from '@immich/sdk';
+
+  let { asset: viewingAsset, gridScrollTarget, mutex, preloadAssets } = assetViewingStore;
+
+  interface Props {
+    timelineManager: TimelineManager;
+    showSkeleton: boolean;
+    withStacked?: boolean;
+    isShared?: boolean;
+    album?: AlbumResponseDto | null;
+    person?: PersonResponseDto | null;
+
+    removeAction?:
+      | AssetAction.UNARCHIVE
+      | AssetAction.ARCHIVE
+      | AssetAction.FAVORITE
+      | AssetAction.UNFAVORITE
+      | AssetAction.SET_VISIBILITY_TIMELINE
+      | null;
+  }
+
+  let {
+    timelineManager,
+    showSkeleton = $bindable(false),
+    removeAction,
+    withStacked = false,
+    isShared = false,
+    album = null,
+    person = null,
+  }: Props = $props();
+
+  const handlePrevious = async () => {
+    const release = await mutex.acquire();
+    const laterAsset = await timelineManager.getLaterAsset($viewingAsset);
+
+    if (laterAsset) {
+      const preloadAsset = await timelineManager.getLaterAsset(laterAsset);
+      const asset = await getAssetInfo({ ...authManager.params, id: laterAsset.id });
+      assetViewingStore.setAsset(asset, preloadAsset ? [preloadAsset] : []);
+      await navigate({ targetRoute: 'current', assetId: laterAsset.id });
+    }
+
+    release();
+    return !!laterAsset;
+  };
+
+  const handleNext = async () => {
+    const release = await mutex.acquire();
+    const earlierAsset = await timelineManager.getEarlierAsset($viewingAsset);
+
+    if (earlierAsset) {
+      const preloadAsset = await timelineManager.getEarlierAsset(earlierAsset);
+      const asset = await getAssetInfo({ ...authManager.params, id: earlierAsset.id });
+      assetViewingStore.setAsset(asset, preloadAsset ? [preloadAsset] : []);
+      await navigate({ targetRoute: 'current', assetId: earlierAsset.id });
+    }
+
+    release();
+    return !!earlierAsset;
+  };
+
+  const handleRandom = async () => {
+    const randomAsset = await timelineManager.getRandomAsset();
+
+    if (randomAsset) {
+      const asset = await getAssetInfo({ ...authManager.params, id: randomAsset.id });
+      assetViewingStore.setAsset(asset);
+      await navigate({ targetRoute: 'current', assetId: randomAsset.id });
+      return asset;
+    }
+  };
+
+  const handleClose = async (asset: { id: string }) => {
+    assetViewingStore.showAssetViewer(false);
+    showSkeleton = true;
+    $gridScrollTarget = { at: asset.id };
+    await navigate({ targetRoute: 'current', assetId: null, assetGridRouteSearchParams: $gridScrollTarget });
+  };
+
+  const handlePreAction = async (action: Action) => {
+    switch (action.type) {
+      case removeAction:
+      case AssetAction.TRASH:
+      case AssetAction.RESTORE:
+      case AssetAction.DELETE:
+      case AssetAction.ARCHIVE:
+      case AssetAction.SET_VISIBILITY_LOCKED:
+      case AssetAction.SET_VISIBILITY_TIMELINE: {
+        // find the next asset to show or close the viewer
+        // eslint-disable-next-line @typescript-eslint/no-unused-expressions
+        (await handleNext()) || (await handlePrevious()) || (await handleClose(action.asset));
+
+        // delete after find the next one
+        timelineManager.removeAssets([action.asset.id]);
+        break;
+      }
+    }
+  };
+  const handleAction = (action: Action) => {
+    switch (action.type) {
+      case AssetAction.ARCHIVE:
+      case AssetAction.UNARCHIVE:
+      case AssetAction.FAVORITE:
+      case AssetAction.UNFAVORITE: {
+        timelineManager.upsertAssets([action.asset]);
+        break;
+      }
+
+      case AssetAction.ADD: {
+        timelineManager.upsertAssets([action.asset]);
+        break;
+      }
+
+      case AssetAction.UNSTACK: {
+        updateUnstackedAssetInTimeline(timelineManager, action.assets);
+        break;
+      }
+      case AssetAction.REMOVE_ASSET_FROM_STACK: {
+        timelineManager.upsertAssets([toTimelineAsset(action.asset)]);
+        if (action.stack) {
+          //Have to unstack then restack assets in timeline in order to update the stack count in the timeline.
+          updateUnstackedAssetInTimeline(
+            timelineManager,
+            action.stack.assets.map((asset) => toTimelineAsset(asset)),
+          );
+          updateStackedAssetInTimeline(timelineManager, {
+            stack: action.stack,
+            toDeleteIds: action.stack.assets
+              .filter((asset) => asset.id !== action.stack?.primaryAssetId)
+              .map((asset) => asset.id),
+          });
+        }
+        break;
+      }
+      case AssetAction.SET_STACK_PRIMARY_ASSET: {
+        //Have to unstack then restack assets in timeline in order for the currently removed new primary asset to be made visible.
+        updateUnstackedAssetInTimeline(
+          timelineManager,
+          action.stack.assets.map((asset) => toTimelineAsset(asset)),
+        );
+        updateStackedAssetInTimeline(timelineManager, {
+          stack: action.stack,
+          toDeleteIds: action.stack.assets
+            .filter((asset) => asset.id !== action.stack.primaryAssetId)
+            .map((asset) => asset.id),
+        });
+        break;
+      }
+    }
+  };
+</script>
+
+{#await import('../asset-viewer/asset-viewer.svelte') then { default: AssetViewer }}
+  <AssetViewer
+    {withStacked}
+    asset={$viewingAsset}
+    preloadAssets={$preloadAssets}
+    {isShared}
+    {album}
+    {person}
+    preAction={handlePreAction}
+    onAction={handleAction}
+    onPrevious={handlePrevious}
+    onNext={handleNext}
+    onRandom={handleRandom}
+    onClose={handleClose}
+  />
+{/await}

web/src/lib/components/timeline/TimelineDateGroup.svelte

@@ -1,254 +0,0 @@
-<script lang="ts">
-  import Thumbnail from '$lib/components/assets/thumbnail/thumbnail.svelte';
-  import type { DayGroup } from '$lib/managers/timeline-manager/day-group.svelte';
-  import type { MonthGroup } from '$lib/managers/timeline-manager/month-group.svelte';
-  import type { TimelineManager } from '$lib/managers/timeline-manager/timeline-manager.svelte';
-  import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
-  import { assetSnapshot, assetsSnapshot } from '$lib/managers/timeline-manager/utils.svelte';
-  import type { AssetInteraction } from '$lib/stores/asset-interaction.svelte';
-  import { isSelectingAllAssets } from '$lib/stores/assets-store.svelte';
-  import { uploadAssetsStore } from '$lib/stores/upload';
-  import { navigate } from '$lib/utils/navigation';
-
-  import { mdiCheckCircle, mdiCircleOutline } from '@mdi/js';
-
-  import { fromTimelinePlainDate, getDateLocaleString } from '$lib/utils/timeline-util';
-  import { Icon } from '@immich/ui';
-  import type { Snippet } from 'svelte';
-  import { flip } from 'svelte/animate';
-  import { scale } from 'svelte/transition';
-
-  let { isUploading } = uploadAssetsStore;
-
-  interface Props {
-    isSelectionMode: boolean;
-    singleSelect: boolean;
-    withStacked: boolean;
-    showArchiveIcon: boolean;
-    monthGroup: MonthGroup;
-    timelineManager: TimelineManager;
-    assetInteraction: AssetInteraction;
-    customLayout?: Snippet<[TimelineAsset]>;
-
-    onSelect: ({ title, assets }: { title: string; assets: TimelineAsset[] }) => void;
-    onSelectAssets: (asset: TimelineAsset) => void;
-    onSelectAssetCandidates: (asset: TimelineAsset | null) => void;
-    onScrollCompensation: (compensation: { heightDelta?: number; scrollTop?: number }) => void;
-    onThumbnailClick?: (
-      asset: TimelineAsset,
-      timelineManager: TimelineManager,
-      dayGroup: DayGroup,
-      onClick: (
-        timelineManager: TimelineManager,
-        assets: TimelineAsset[],
-        groupTitle: string,
-        asset: TimelineAsset,
-      ) => void,
-    ) => void;
-  }
-
-  let {
-    isSelectionMode,
-    singleSelect,
-    withStacked,
-    showArchiveIcon,
-    monthGroup = $bindable(),
-    assetInteraction,
-    timelineManager,
-    customLayout,
-    onSelect,
-    onSelectAssets,
-    onSelectAssetCandidates,
-    onScrollCompensation,
-    onThumbnailClick,
-  }: Props = $props();
-
-  let isMouseOverGroup = $state(false);
-  let hoveredDayGroup = $state();
-
-  const transitionDuration = $derived.by(() =>
-    monthGroup.timelineManager.suspendTransitions && !$isUploading ? 0 : 150,
-  );
-  const scaleDuration = $derived(transitionDuration === 0 ? 0 : transitionDuration + 100);
-  const _onClick = (
-    timelineManager: TimelineManager,
-    assets: TimelineAsset[],
-    groupTitle: string,
-    asset: TimelineAsset,
-  ) => {
-    if (isSelectionMode || assetInteraction.selectionActive) {
-      assetSelectHandler(timelineManager, asset, assets, groupTitle);
-      return;
-    }
-    void navigate({ targetRoute: 'current', assetId: asset.id });
-  };
-
-  const handleSelectGroup = (title: string, assets: TimelineAsset[]) => onSelect({ title, assets });
-
-  const assetSelectHandler = (
-    timelineManager: TimelineManager,
-    asset: TimelineAsset,
-    assetsInDayGroup: TimelineAsset[],
-    groupTitle: string,
-  ) => {
-    onSelectAssets(asset);
-
-    // Check if all assets are selected in a group to toggle the group selection's icon
-    let selectedAssetsInGroupCount = assetsInDayGroup.filter((asset) =>
-      assetInteraction.hasSelectedAsset(asset.id),
-    ).length;
-
-    // if all assets are selected in a group, add the group to selected group
-    if (selectedAssetsInGroupCount == assetsInDayGroup.length) {
-      assetInteraction.addGroupToMultiselectGroup(groupTitle);
-    } else {
-      assetInteraction.removeGroupFromMultiselectGroup(groupTitle);
-    }
-
-    if (timelineManager.assetCount == assetInteraction.selectedAssets.length) {
-      isSelectingAllAssets.set(true);
-    } else {
-      isSelectingAllAssets.set(false);
-    }
-  };
-
-  const assetMouseEventHandler = (groupTitle: string, asset: TimelineAsset | null) => {
-    // Show multi select icon on hover on date group
-    hoveredDayGroup = groupTitle;
-
-    if (assetInteraction.selectionActive) {
-      onSelectAssetCandidates(asset);
-    }
-  };
-
-  function filterIntersecting<R extends { intersecting: boolean }>(intersectable: R[]) {
-    return intersectable.filter((int) => int.intersecting);
-  }
-
-  const getDayGroupFullDate = (dayGroup: DayGroup): string => {
-    const { month, year } = dayGroup.monthGroup.yearMonth;
-    const date = fromTimelinePlainDate({
-      year,
-      month,
-      day: dayGroup.day,
-    });
-    return getDateLocaleString(date);
-  };
-
-  $effect.root(() => {
-    if (timelineManager.scrollCompensation.monthGroup === monthGroup) {
-      onScrollCompensation(timelineManager.scrollCompensation);
-      timelineManager.clearScrollCompensation();
-    }
-  });
-</script>
-
-{#each filterIntersecting(monthGroup.dayGroups) as dayGroup, groupIndex (dayGroup.day)}
-  {@const absoluteWidth = dayGroup.left}
-
-  <!-- svelte-ignore a11y_no_static_element_interactions -->
-  <section
-    class={[
-      { 'transition-all': !monthGroup.timelineManager.suspendTransitions },
-      !monthGroup.timelineManager.suspendTransitions && `delay-${transitionDuration}`,
-    ]}
-    data-group
-    style:position="absolute"
-    style:transform={`translate3d(${absoluteWidth}px,${dayGroup.top}px,0)`}
-    onmouseenter={() => {
-      isMouseOverGroup = true;
-      assetMouseEventHandler(dayGroup.groupTitle, null);
-    }}
-    onmouseleave={() => {
-      isMouseOverGroup = false;
-      assetMouseEventHandler(dayGroup.groupTitle, null);
-    }}
-  >
-    <!-- Date group title -->
-    <div
-      class="flex pt-7 pb-5 max-md:pt-5 max-md:pb-3 h-6 place-items-center text-xs font-medium text-immich-fg dark:text-immich-dark-fg md:text-sm"
-      style:width={dayGroup.width + 'px'}
-    >
-      {#if !singleSelect}
-        <div
-          class="hover:cursor-pointer transition-all duration-200 ease-out overflow-hidden w-0"
-          class:w-8={(hoveredDayGroup === dayGroup.groupTitle && isMouseOverGroup) ||
-            assetInteraction.selectedGroup.has(dayGroup.groupTitle)}
-          onclick={() => handleSelectGroup(dayGroup.groupTitle, assetsSnapshot(dayGroup.getAssets()))}
-          onkeydown={() => handleSelectGroup(dayGroup.groupTitle, assetsSnapshot(dayGroup.getAssets()))}
-        >
-          {#if assetInteraction.selectedGroup.has(dayGroup.groupTitle)}
-            <Icon icon={mdiCheckCircle} size="24" class="text-primary" />
-          {:else}
-            <Icon icon={mdiCircleOutline} size="24" color="#757575" />
-          {/if}
-        </div>
-      {/if}
-
-      <span class="w-full truncate first-letter:capitalize" title={getDayGroupFullDate(dayGroup)}>
-        {dayGroup.groupTitle}
-      </span>
-    </div>
-
-    <!-- Image grid -->
-    <div
-      data-image-grid
-      class="relative overflow-clip"
-      style:height={dayGroup.height + 'px'}
-      style:width={dayGroup.width + 'px'}
-    >
-      {#each filterIntersecting(dayGroup.viewerAssets) as viewerAsset (viewerAsset.id)}
-        {@const position = viewerAsset.position!}
-        {@const asset = viewerAsset.asset!}
-
-        <!-- {#if viewerAsset.intersecting} -->
-        <!-- note: don't remove data-asset-id - its used by web e2e tests -->
-        <div
-          data-asset-id={asset.id}
-          class="absolute"
-          style:top={position.top + 'px'}
-          style:left={position.left + 'px'}
-          style:width={position.width + 'px'}
-          style:height={position.height + 'px'}
-          out:scale|global={{ start: 0.1, duration: scaleDuration }}
-          animate:flip={{ duration: transitionDuration }}
-        >
-          <Thumbnail
-            showStackedIcon={withStacked}
-            {showArchiveIcon}
-            {asset}
-            {groupIndex}
-            onClick={(asset) => {
-              if (typeof onThumbnailClick === 'function') {
-                onThumbnailClick(asset, timelineManager, dayGroup, _onClick);
-              } else {
-                _onClick(timelineManager, dayGroup.getAssets(), dayGroup.groupTitle, asset);
-              }
-            }}
-            onSelect={(asset) => assetSelectHandler(timelineManager, asset, dayGroup.getAssets(), dayGroup.groupTitle)}
-            onMouseEvent={() => assetMouseEventHandler(dayGroup.groupTitle, assetSnapshot(asset))}
-            selected={assetInteraction.hasSelectedAsset(asset.id) ||
-              dayGroup.monthGroup.timelineManager.albumAssets.has(asset.id)}
-            selectionCandidate={assetInteraction.hasSelectionCandidate(asset.id)}
-            disabled={dayGroup.monthGroup.timelineManager.albumAssets.has(asset.id)}
-            thumbnailWidth={position.width}
-            thumbnailHeight={position.height}
-          />
-          {#if customLayout}
-            {@render customLayout(asset)}
-          {/if}
-        </div>
-        <!-- {/if} -->
-      {/each}
-    </div>
-  </section>
-{/each}
-
-<style>
-  section {
-    contain: layout paint style;
-  }
-  [data-image-grid] {
-    user-select: none;
-  }
-</style>

web/src/lib/components/timeline/actions/ArchiveAction.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
   import { getAssetControlContext } from '$lib/components/timeline/AssetSelectControlBar.svelte';
+  import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
   import type { OnArchive } from '$lib/utils/actions';
   import { archiveAssets } from '$lib/utils/asset-utils';
   import { AssetVisibility } from '@immich/sdk';
@@ -12,9 +13,10 @@
     onArchive?: OnArchive;
     menuItem?: boolean;
     unarchive?: boolean;
+    manager?: PhotostreamManager;
   }
 
-  let { onArchive, menuItem = false, unarchive = false }: Props = $props();
+  let { onArchive, menuItem = false, unarchive = false, manager }: Props = $props();
 
   let text = $derived(unarchive ? $t('unarchive') : $t('to_archive'));
   let icon = $derived(unarchive ? mdiArchiveArrowUpOutline : mdiArchiveArrowDownOutline);
@@ -24,12 +26,13 @@
   const { clearSelect, getOwnedAssets } = getAssetControlContext();
 
   const handleArchive = async () => {
-    const isArchived = unarchive ? AssetVisibility.Timeline : AssetVisibility.Archive;
-    const assets = [...getOwnedAssets()].filter((asset) => asset.visibility !== isArchived);
+    const visibility = unarchive ? AssetVisibility.Timeline : AssetVisibility.Archive;
+    const assets = [...getOwnedAssets()].filter((asset) => asset.visibility !== visibility);
     loading = true;
-    const ids = await archiveAssets(assets, isArchived as AssetVisibility);
+    const ids = await archiveAssets(assets, visibility as AssetVisibility);
     if (ids) {
-      onArchive?.(ids, isArchived ? AssetVisibility.Archive : AssetVisibility.Timeline);
+      manager?.updateAssetOperation(ids, (asset) => ((asset.visibility = visibility), void 0));
+      onArchive?.(ids, visibility ? AssetVisibility.Archive : AssetVisibility.Timeline);
       clearSelect();
     }
     loading = false;

web/src/lib/components/timeline/actions/DeleteAssetsAction.svelte

@@ -1,6 +1,8 @@
 <script lang="ts">
   import DeleteAssetDialog from '$lib/components/photos-page/delete-asset-dialog.svelte';
   import { getAssetControlContext } from '$lib/components/timeline/AssetSelectControlBar.svelte';
+  import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
+  import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
   import { featureFlags } from '$lib/stores/server-config.store';
   import { type OnDelete, type OnUndoDelete, deleteAssets } from '$lib/utils/actions';
   import { IconButton } from '@immich/ui';
@@ -9,13 +11,14 @@
   import MenuOption from '../../shared-components/context-menu/menu-option.svelte';
 
   interface Props {
-    onAssetDelete: OnDelete;
-    onUndoDelete?: OnUndoDelete | undefined;
+    onAssetDelete?: OnDelete;
+    onUndoDelete?: OnUndoDelete;
     menuItem?: boolean;
     force?: boolean;
+    manager?: PhotostreamManager;
   }
 
-  let { onAssetDelete, onUndoDelete = undefined, menuItem = false, force = !$featureFlags.trash }: Props = $props();
+  let { onAssetDelete, onUndoDelete, menuItem = false, force = !$featureFlags.trash, manager }: Props = $props();
 
   const { clearSelect, getOwnedAssets } = getAssetControlContext();
 
@@ -36,7 +39,12 @@
   const handleDelete = async () => {
     loading = true;
     const assets = [...getOwnedAssets()];
-    await deleteAssets(force, onAssetDelete, assets, onUndoDelete);
+    const undo = (assets: TimelineAsset[]) => {
+      manager?.upsertAssets(assets);
+      onUndoDelete?.(assets);
+    };
+    await deleteAssets(force, onAssetDelete, assets, undo);
+    manager?.removeAssets(assets.map((asset) => asset.id));
     clearSelect();
     isShowConfirmation = false;
     loading = false;

web/src/lib/components/timeline/actions/FavoriteAction.svelte

@@ -5,6 +5,7 @@
     notificationController,
   } from '$lib/components/shared-components/notification/notification';
   import { getAssetControlContext } from '$lib/components/timeline/AssetSelectControlBar.svelte';
+  import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
   import type { OnFavorite } from '$lib/utils/actions';
   import { handleError } from '$lib/utils/handle-error';
   import { updateAssets } from '@immich/sdk';
@@ -16,9 +17,10 @@
     onFavorite?: OnFavorite;
     menuItem?: boolean;
     removeFavorite: boolean;
+    manager?: PhotostreamManager;
   }
 
-  let { onFavorite, menuItem = false, removeFavorite }: Props = $props();
+  let { onFavorite, menuItem = false, removeFavorite, manager }: Props = $props();
 
   let text = $derived(removeFavorite ? $t('remove_from_favorites') : $t('to_favorite'));
   let icon = $derived(removeFavorite ? mdiHeartMinusOutline : mdiHeartOutline);
@@ -39,11 +41,7 @@
       if (ids.length > 0) {
         await updateAssets({ assetBulkUpdateDto: { ids, isFavorite } });
       }
-
-      for (const asset of assets) {
-        asset.isFavorite = isFavorite;
-      }
-
+      manager?.updateAssetOperation(ids, (asset) => ((asset.isFavorite = isFavorite), void 0));
       onFavorite?.(ids, isFavorite);
 
       notificationController.show({

web/src/lib/components/timeline/actions/TimelineKeyboardActions.svelte

@@ -51,7 +51,7 @@
       !(isTrashEnabled && !force),
       (assetIds) => timelineManager.removeAssets(assetIds),
       assetInteraction.selectedAssets,
-      !isTrashEnabled || force ? undefined : (assets) => timelineManager.addAssets(assets),
+      !isTrashEnabled || force ? undefined : (assets) => timelineManager.upsertAssets(assets),
     );
     assetInteraction.clearMultiselect();
   };

web/src/lib/managers/photostream-manager/PhotostreamManager.svelte.ts

@@ -0,0 +1,423 @@
+import { updateIntersectionMonthGroup } from '$lib/managers/timeline-manager/internal/intersection-support.svelte';
+import { updateGeometry } from '$lib/managers/timeline-manager/internal/layout-support.svelte';
+import { CancellableTask } from '$lib/utils/cancellable-task';
+import { clamp, debounce } from 'lodash-es';
+
+import {
+  PhotostreamSegment,
+  type SegmentIdentifier,
+} from '$lib/managers/photostream-manager/PhotostreamSegment.svelte';
+
+import { updateObject } from '$lib/managers/timeline-manager/internal/utils.svelte';
+import type {
+  AssetDescriptor,
+  AssetOperation,
+  MoveAsset,
+  TimelineAsset,
+  TimelineManagerLayoutOptions,
+  Viewport,
+} from '$lib/managers/timeline-manager/types';
+import { setDifference } from '$lib/utils/timeline-util';
+
+export abstract class PhotostreamManager {
+  isInitialized = $state(false);
+  topSectionHeight = $state(0);
+  bottomSectionHeight = $state(60);
+  abstract get months(): PhotostreamSegment[];
+  timelineHeight = $derived.by(
+    () => this.months.reduce((accumulator, b) => accumulator + b.height, 0) + this.topSectionHeight,
+  );
+  assetCount = $derived.by(() => this.months.reduce((accumulator, b) => accumulator + b.assetsCount, 0));
+
+  topIntersectingMonthGroup: PhotostreamSegment | undefined = $state();
+
+  visibleWindow = $derived.by(() => ({
+    top: this.#scrollTop,
+    bottom: this.#scrollTop + this.viewportHeight,
+  }));
+
+  protected initTask = new CancellableTask(
+    () => (this.isInitialized = true),
+    () => (this.isInitialized = false),
+    () => void 0,
+  );
+
+  #viewportHeight = $state(0);
+  #viewportWidth = $state(0);
+  #scrollTop = $state(0);
+
+  #rowHeight = $state(235);
+  #headerHeight = $state(48);
+  #gap = $state(12);
+
+  #scrolling = $state(false);
+  #suspendTransitions = $state(false);
+  #resetScrolling = debounce(() => (this.#scrolling = false), 1000);
+  #resetSuspendTransitions = debounce(() => (this.suspendTransitions = false), 1000);
+  scrollCompensation: {
+    heightDelta: number | undefined;
+    scrollTop: number | undefined;
+    monthGroup: PhotostreamSegment | undefined;
+  } = $state({
+    heightDelta: 0,
+    scrollTop: 0,
+    monthGroup: undefined,
+  });
+
+  constructor() {}
+
+  setLayoutOptions({ headerHeight = 48, rowHeight = 235, gap = 12 }: TimelineManagerLayoutOptions) {
+    let changed = false;
+    changed ||= this.#setHeaderHeight(headerHeight);
+    changed ||= this.#setGap(gap);
+    changed ||= this.#setRowHeight(rowHeight);
+    if (changed) {
+      this.refreshLayout();
+    }
+  }
+
+  #setHeaderHeight(value: number) {
+    if (this.#headerHeight == value) {
+      return false;
+    }
+    this.#headerHeight = value;
+    return true;
+  }
+
+  get headerHeight() {
+    return this.#headerHeight;
+  }
+
+  #setGap(value: number) {
+    if (this.#gap == value) {
+      return false;
+    }
+    this.#gap = value;
+    return true;
+  }
+
+  get gap() {
+    return this.#gap;
+  }
+
+  #setRowHeight(value: number) {
+    if (this.#rowHeight == value) {
+      return false;
+    }
+    this.#rowHeight = value;
+    return true;
+  }
+
+  get rowHeight() {
+    return this.#rowHeight;
+  }
+
+  set scrolling(value: boolean) {
+    this.#scrolling = value;
+    if (value) {
+      this.suspendTransitions = true;
+      this.#resetScrolling();
+    }
+  }
+
+  get scrolling() {
+    return this.#scrolling;
+  }
+
+  set suspendTransitions(value: boolean) {
+    this.#suspendTransitions = value;
+    if (value) {
+      this.#resetSuspendTransitions();
+    }
+  }
+
+  get suspendTransitions() {
+    return this.#suspendTransitions;
+  }
+
+  set viewportWidth(value: number) {
+    const changed = value !== this.#viewportWidth;
+    this.#viewportWidth = value;
+    this.suspendTransitions = true;
+    void this.updateViewportGeometry(changed);
+  }
+
+  get viewportWidth() {
+    return this.#viewportWidth;
+  }
+
+  set viewportHeight(value: number) {
+    this.#viewportHeight = value;
+    this.#suspendTransitions = true;
+    void this.updateViewportGeometry(false);
+  }
+
+  get viewportHeight() {
+    return this.#viewportHeight;
+  }
+
+  updateSlidingWindow(scrollTop: number) {
+    if (this.#scrollTop !== scrollTop) {
+      this.#scrollTop = scrollTop;
+      this.updateIntersections();
+    }
+  }
+
+  clearScrollCompensation() {
+    this.scrollCompensation = {
+      heightDelta: undefined,
+      scrollTop: undefined,
+      monthGroup: undefined,
+    };
+  }
+
+  updateIntersections() {
+    if (!this.isInitialized || this.visibleWindow.bottom === this.visibleWindow.top) {
+      return;
+    }
+    let topIntersectingMonthGroup = undefined;
+    for (const month of this.months) {
+      updateIntersectionMonthGroup(this, month);
+      if (!topIntersectingMonthGroup && month.actuallyIntersecting) {
+        topIntersectingMonthGroup = month;
+      }
+    }
+    if (topIntersectingMonthGroup !== undefined && this.topIntersectingMonthGroup !== topIntersectingMonthGroup) {
+      this.topIntersectingMonthGroup = topIntersectingMonthGroup;
+    }
+    for (const month of this.months) {
+      if (month === this.topIntersectingMonthGroup) {
+        this.topIntersectingMonthGroup.percent = clamp(
+          (this.visibleWindow.top - this.topIntersectingMonthGroup.top) / this.topIntersectingMonthGroup.height,
+          0,
+          1,
+        );
+      } else {
+        month.percent = 0;
+      }
+    }
+  }
+
+  async init() {
+    this.isInitialized = false;
+    await this.initTask.execute(() => Promise.resolve(undefined), true);
+  }
+
+  public destroy() {
+    this.isInitialized = false;
+  }
+
+  async updateViewport(viewport: Viewport) {
+    if (viewport.height === 0 && viewport.width === 0) {
+      return;
+    }
+
+    if (this.viewportHeight === viewport.height && this.viewportWidth === viewport.width) {
+      return;
+    }
+
+    if (!this.initTask.executed) {
+      await (this.initTask.loading ? this.initTask.waitUntilCompletion() : this.init());
+    }
+
+    const changedWidth = viewport.width !== this.viewportWidth;
+    this.viewportHeight = viewport.height;
+    this.viewportWidth = viewport.width;
+    this.updateViewportGeometry(changedWidth);
+  }
+
+  protected updateViewportGeometry(changedWidth: boolean) {
+    if (!this.isInitialized) {
+      return;
+    }
+    if (this.viewportWidth === 0 || this.viewportHeight === 0) {
+      return;
+    }
+    for (const month of this.months) {
+      updateGeometry(this, month, { invalidateHeight: changedWidth });
+    }
+    this.updateIntersections();
+  }
+
+  createLayoutOptions() {
+    const viewportWidth = this.viewportWidth;
+
+    return {
+      spacing: 2,
+      heightTolerance: 0.15,
+      rowHeight: this.#rowHeight,
+      rowWidth: Math.floor(viewportWidth),
+    };
+  }
+
+  async loadSegment(identifier: SegmentIdentifier, options?: { cancelable: boolean }): Promise<void> {
+    let cancelable = true;
+    if (options) {
+      cancelable = options.cancelable;
+    }
+    const segment = this.getSegmentByIdentifier(identifier);
+    if (!segment) {
+      return;
+    }
+
+    if (segment.loader?.executed) {
+      return;
+    }
+
+    const result = await segment.load(cancelable);
+    if (result === 'LOADED') {
+      updateIntersectionMonthGroup(this, segment);
+    }
+  }
+
+  getSegmentByIdentifier(identifier: SegmentIdentifier) {
+    return this.months.find((segment) => identifier.matches(segment));
+  }
+
+  getSegmentForAssetId(assetId: string) {
+    for (const month of this.months) {
+      const asset = month.assets.find((asset) => asset.id === assetId);
+      if (asset) {
+        return month;
+      }
+    }
+  }
+
+  refreshLayout() {
+    for (const month of this.months) {
+      updateGeometry(this, month, { invalidateHeight: true });
+    }
+    this.updateIntersections();
+  }
+
+  getMaxScrollPercent() {
+    const totalHeight = this.timelineHeight + this.bottomSectionHeight + this.topSectionHeight;
+    return (totalHeight - this.viewportHeight) / totalHeight;
+  }
+
+  getMaxScroll() {
+    return this.topSectionHeight + this.bottomSectionHeight + (this.timelineHeight - this.viewportHeight);
+  }
+
+  retrieveRange(start: AssetDescriptor, end: AssetDescriptor): Promise<TimelineAsset[]> {
+    const range: TimelineAsset[] = [];
+    let collecting = false;
+
+    for (const month of this.months) {
+      for (const asset of month.assets) {
+        if (asset.id === start.id) {
+          collecting = true;
+        }
+        if (collecting) {
+          range.push(asset);
+        }
+        if (asset.id === end.id) {
+          return Promise.resolve(range);
+        }
+      }
+    }
+    return Promise.resolve(range);
+  }
+
+  updateAssetOperation(ids: string[], operation: AssetOperation) {
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    return this.#runAssetOperation(new Set(ids), operation);
+  }
+
+  upsertAssets(assets: TimelineAsset[]) {
+    const notExcluded = assets.filter((asset) => !this.isExcluded(asset));
+    const notUpdated = this.#updateAssets(notExcluded);
+    this.addAssetsToSegments([...notUpdated]);
+  }
+
+  #updateAssets(assets: TimelineAsset[]) {
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    const lookup = new Map<string, TimelineAsset>(assets.map((asset) => [asset.id, asset]));
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    const { unprocessedIds } = this.#runAssetOperation(new Set(lookup.keys()), (asset) =>
+      updateObject(asset, lookup.get(asset.id)),
+    );
+    const result: TimelineAsset[] = [];
+    for (const id of unprocessedIds.values()) {
+      result.push(lookup.get(id)!);
+    }
+    return result;
+  }
+
+  removeAssets(ids: string[]) {
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    const { unprocessedIds } = this.#runAssetOperation(new Set(ids), () => ({ remove: true }));
+    return [...unprocessedIds];
+  }
+
+  isExcluded(_: TimelineAsset) {
+    return false;
+  }
+
+  protected createUpsertContext(): unknown {
+    return;
+  }
+
+  protected abstract upsertAssetIntoSegment(asset: TimelineAsset, context: unknown): void;
+
+  protected postCreateSegments(): void {}
+
+  protected postUpsert(_: unknown): void {}
+
+  protected addAssetsToSegments(assets: TimelineAsset[]) {
+    if (assets.length === 0) {
+      return;
+    }
+    const context = this.createUpsertContext();
+    const monthCount = this.months.length;
+    for (const asset of assets) {
+      this.upsertAssetIntoSegment(asset, context);
+    }
+    if (this.months.length !== monthCount) {
+      this.postCreateSegments();
+    }
+    this.postUpsert(context);
+    this.updateIntersections();
+  }
+
+  #runAssetOperation(ids: Set<string>, operation: AssetOperation) {
+    if (ids.size === 0) {
+      // eslint-disable-next-line svelte/prefer-svelte-reactivity
+      return { processedIds: new Set(), unprocessedIds: ids, changedGeometry: false };
+    }
+
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    const changedMonthGroups = new Set<PhotostreamSegment>();
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    let idsToProcess = new Set(ids);
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    const idsProcessed = new Set<string>();
+    const combinedMoveAssets: MoveAsset[][] = [];
+    for (const month of this.months) {
+      if (idsToProcess.size > 0) {
+        const { moveAssets, processedIds, changedGeometry } = month.runAssetOperation(idsToProcess, operation);
+        if (moveAssets.length > 0) {
+          combinedMoveAssets.push(moveAssets);
+        }
+        idsToProcess = setDifference(idsToProcess, processedIds);
+        for (const id of processedIds) {
+          idsProcessed.add(id);
+        }
+        if (changedGeometry) {
+          changedMonthGroups.add(month);
+        }
+      }
+    }
+    if (combinedMoveAssets.length > 0) {
+      this.addAssetsToSegments(combinedMoveAssets.flat().map((a) => a.asset));
+    }
+    const changedGeometry = changedMonthGroups.size > 0;
+    for (const month of changedMonthGroups) {
+      updateGeometry(this, month, { invalidateHeight: true });
+    }
+    if (changedGeometry) {
+      this.updateIntersections();
+    }
+    return { unprocessedIds: idsToProcess, processedIds: idsProcessed, changedGeometry };
+  }
+}

web/src/lib/managers/photostream-manager/PhotostreamSegment.svelte.ts

@@ -0,0 +1,195 @@
+import { CancellableTask } from '$lib/utils/cancellable-task';
+import { handleError } from '$lib/utils/handle-error';
+import { t } from 'svelte-i18n';
+import { get } from 'svelte/store';
+
+import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
+import type { AssetOperation, MoveAsset, TimelineAsset } from '$lib/managers/timeline-manager/types';
+import type { ViewerAsset } from '$lib/managers/timeline-manager/viewer-asset.svelte';
+
+export type SegmentIdentifier = {
+  matches(segment: PhotostreamSegment): boolean;
+};
+export abstract class PhotostreamSegment {
+  #intersecting = $state(false);
+  actuallyIntersecting = $state(false);
+  #isLoaded = $state(false);
+
+  #height = $state(0);
+  #top = $state(0);
+  #assets = $derived.by(() => this.viewerAssets.map((viewerAsset) => viewerAsset.asset));
+
+  initialCount = $state(0);
+  percent = $state(0);
+
+  assetsCount = $derived.by(() => (this.isLoaded ? this.viewerAssets.length : this.initialCount));
+  loader = new CancellableTask(
+    () => this.markLoaded(),
+    () => this.markCanceled,
+    () => this.handleLoadError,
+  );
+  isHeightActual = $state(false);
+
+  abstract get timelineManager(): PhotostreamManager;
+
+  abstract get identifier(): SegmentIdentifier;
+
+  abstract get id(): string;
+
+  get isLoaded() {
+    return this.#isLoaded;
+  }
+
+  protected markLoaded() {
+    this.#isLoaded = true;
+  }
+
+  protected markCanceled() {
+    this.#isLoaded = false;
+  }
+
+  set intersecting(newValue: boolean) {
+    const old = this.#intersecting;
+    if (old === newValue) {
+      return;
+    }
+    this.#intersecting = newValue;
+    if (newValue) {
+      void this.load(true);
+    } else {
+      this.cancel();
+    }
+  }
+
+  get intersecting() {
+    return this.#intersecting;
+  }
+
+  async load(cancelable: boolean): Promise<'DONE' | 'WAITED' | 'CANCELED' | 'LOADED' | 'ERRORED'> {
+    return await this.loader?.execute(async (signal: AbortSignal) => {
+      await this.fetch(signal);
+    }, cancelable);
+  }
+
+  protected abstract fetch(signal: AbortSignal): Promise<void>;
+
+  get assets(): TimelineAsset[] {
+    return this.#assets;
+  }
+
+  abstract get viewerAssets(): ViewerAsset[];
+
+  set height(height: number) {
+    if (this.#height === height) {
+      return;
+    }
+    const { timelineManager: store, percent } = this;
+    const index = store.months.indexOf(this);
+    const heightDelta = height - this.#height;
+    this.#height = height;
+    const prevMonthGroup = store.months[index - 1];
+    if (prevMonthGroup) {
+      const newTop = prevMonthGroup.#top + prevMonthGroup.#height;
+      if (this.#top !== newTop) {
+        this.#top = newTop;
+      }
+    }
+    for (let cursor = index + 1; cursor < store.months.length; cursor++) {
+      const monthGroup = this.timelineManager.months[cursor];
+      const newTop = monthGroup.#top + heightDelta;
+      if (monthGroup.#top !== newTop) {
+        monthGroup.#top = newTop;
+      }
+    }
+    if (store.topIntersectingMonthGroup) {
+      const currentIndex = store.months.indexOf(store.topIntersectingMonthGroup);
+      if (currentIndex > 0) {
+        if (index < currentIndex) {
+          store.scrollCompensation = {
+            heightDelta,
+            scrollTop: undefined,
+            monthGroup: this,
+          };
+        } else if (percent > 0) {
+          const top = this.top + height * percent;
+          store.scrollCompensation = {
+            heightDelta: undefined,
+            scrollTop: top,
+            monthGroup: this,
+          };
+        }
+      }
+    }
+  }
+
+  get height() {
+    return this.#height;
+  }
+
+  get top(): number {
+    return this.#top + this.timelineManager.topSectionHeight;
+  }
+
+  protected handleLoadError(error: unknown) {
+    const _$t = get(t);
+    handleError(error, _$t('errors.failed_to_load_assets'));
+  }
+
+  cancel() {
+    this.loader?.cancel();
+  }
+
+  layout(_: boolean) {}
+
+  updateIntersection({ intersecting, actuallyIntersecting }: { intersecting: boolean; actuallyIntersecting: boolean }) {
+    this.intersecting = intersecting;
+    this.actuallyIntersecting = actuallyIntersecting;
+  }
+
+  abstract findAssetAbsolutePosition(assetId: string): number;
+
+  runAssetOperation(ids: Set<string>, operation: AssetOperation) {
+    if (ids.size === 0) {
+      return {
+        moveAssets: [] as MoveAsset[],
+        // eslint-disable-next-line svelte/prefer-svelte-reactivity
+        processedIds: new Set<string>(),
+        unprocessedIds: ids,
+        changedGeometry: false,
+      };
+    }
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    const unprocessedIds = new Set<string>(ids);
+    // eslint-disable-next-line svelte/prefer-svelte-reactivity
+    const processedIds = new Set<string>();
+    const moveAssets: MoveAsset[] = [];
+    let changedGeometry = false;
+    for (const assetId of unprocessedIds) {
+      const index = this.viewerAssets.findIndex((viewAsset) => viewAsset.id == assetId);
+      if (index === -1) {
+        continue;
+      }
+
+      const asset = this.viewerAssets[index].asset!;
+      const oldTime = { ...asset.localDateTime };
+      const opResult = operation(asset);
+      let remove = false;
+      if (opResult) {
+        remove = (opResult as { remove: boolean }).remove ?? false;
+      }
+      const newTime = asset.localDateTime;
+      if (oldTime.year !== newTime.year || oldTime.month !== newTime.month || oldTime.day !== newTime.day) {
+        const { year, month, day } = newTime;
+        remove = true;
+        moveAssets.push({ asset, date: { year, month, day } });
+      }
+      unprocessedIds.delete(assetId);
+      processedIds.add(assetId);
+      if (remove || this.timelineManager.isExcluded(asset)) {
+        this.viewerAssets.splice(index, 1);
+        changedGeometry = true;
+      }
+    }
+    return { moveAssets, processedIds, unprocessedIds, changedGeometry };
+  }
+}

web/src/lib/managers/timeline-manager/day-group.svelte.ts

@@ -13,6 +13,7 @@ export class DayGroup {
   readonly monthGroup: MonthGroup;
   readonly index: number;
   readonly groupTitle: string;
+  readonly groupTitleFull: string;
   readonly day: number;
   viewerAssets: ViewerAsset[] = $state([]);
 
@@ -26,11 +27,12 @@ export class DayGroup {
   #col = $state(0);
   #deferredLayout = false;
 
-  constructor(monthGroup: MonthGroup, index: number, day: number, groupTitle: string) {
+  constructor(monthGroup: MonthGroup, index: number, day: number, groupTitle: string, groupTitleFull: string) {
     this.index = index;
     this.monthGroup = monthGroup;
     this.day = day;
     this.groupTitle = groupTitle;
+    this.groupTitleFull = groupTitleFull;
   }
 
   get top() {
@@ -127,7 +129,11 @@ export class DayGroup {
 
       const asset = this.viewerAssets[index].asset!;
       const oldTime = { ...asset.localDateTime };
-      let { remove } = operation(asset);
+      const opResult = operation(asset);
+      let remove = false;
+      if (opResult) {
+        remove = (opResult as { remove: boolean }).remove ?? false;
+      }
       const newTime = asset.localDateTime;
       if (oldTime.year !== newTime.year || oldTime.month !== newTime.month || oldTime.day !== newTime.day) {
         const { year, month, day } = newTime;

web/src/lib/managers/timeline-manager/internal/intersection-support.svelte.ts

@@ -1,27 +1,23 @@
+import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
+import type { PhotostreamSegment } from '$lib/managers/photostream-manager/PhotostreamSegment.svelte';
 import { TUNABLES } from '$lib/utils/tunables';
-import type { MonthGroup } from '../month-group.svelte';
-import type { TimelineManager } from '../timeline-manager.svelte';
 
 const {
   TIMELINE: { INTERSECTION_EXPAND_TOP, INTERSECTION_EXPAND_BOTTOM },
 } = TUNABLES;
 
-export function updateIntersectionMonthGroup(timelineManager: TimelineManager, month: MonthGroup) {
-  const actuallyIntersecting = calculateMonthGroupIntersecting(timelineManager, month, 0, 0);
+export function updateIntersectionMonthGroup(timelineManager: PhotostreamManager, month: PhotostreamSegment) {
+  const actuallyIntersecting = calculateSegmentIntersecting(timelineManager, month, 0, 0);
   let preIntersecting = false;
   if (!actuallyIntersecting) {
-    preIntersecting = calculateMonthGroupIntersecting(
+    preIntersecting = calculateSegmentIntersecting(
       timelineManager,
       month,
       INTERSECTION_EXPAND_TOP,
       INTERSECTION_EXPAND_BOTTOM,
     );
   }
-  month.intersecting = actuallyIntersecting || preIntersecting;
-  month.actuallyIntersecting = actuallyIntersecting;
-  if (preIntersecting || actuallyIntersecting) {
-    timelineManager.clearDeferredLayout(month);
-  }
+  month.updateIntersection({ intersecting: actuallyIntersecting || preIntersecting, actuallyIntersecting });
 }
 
 /**
@@ -40,9 +36,9 @@ export function isIntersecting(regionTop: number, regionBottom: number, windowTo
   );
 }
 
-export function calculateMonthGroupIntersecting(
-  timelineManager: TimelineManager,
-  monthGroup: MonthGroup,
+export function calculateSegmentIntersecting(
+  timelineManager: PhotostreamManager,
+  monthGroup: PhotostreamSegment,
   expandTop: number,
   expandBottom: number,
 ) {
@@ -58,7 +54,7 @@ export function calculateMonthGroupIntersecting(
  * Calculate intersection for viewer assets with additional parameters like header height and scroll compensation
  */
 export function calculateViewerAssetIntersecting(
-  timelineManager: TimelineManager,
+  timelineManager: PhotostreamManager,
   positionTop: number,
   positionHeight: number,
   expandTop: number = INTERSECTION_EXPAND_TOP,

web/src/lib/managers/timeline-manager/internal/layout-support.svelte.ts

@@ -1,8 +1,14 @@
+import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
+import type { PhotostreamSegment } from '$lib/managers/photostream-manager/PhotostreamSegment.svelte';
+import type { TimelineManager } from '$lib/managers/timeline-manager/timeline-manager.svelte';
 import type { MonthGroup } from '../month-group.svelte';
-import type { TimelineManager } from '../timeline-manager.svelte';
 import type { UpdateGeometryOptions } from '../types';
 
-export function updateGeometry(timelineManager: TimelineManager, month: MonthGroup, options: UpdateGeometryOptions) {
+export function updateGeometry(
+  timelineManager: PhotostreamManager,
+  month: PhotostreamSegment,
+  options: UpdateGeometryOptions,
+) {
   const { invalidateHeight, noDefer = false } = options;
   if (invalidateHeight) {
     month.isHeightActual = false;
@@ -17,7 +23,7 @@ export function updateGeometry(timelineManager: TimelineManager, month: MonthGro
     }
     return;
   }
-  layoutMonthGroup(timelineManager, month, noDefer);
+  month.layout(noDefer);
 }
 
 export function layoutMonthGroup(timelineManager: TimelineManager, month: MonthGroup, noDefer: boolean = false) {

web/src/lib/managers/timeline-manager/internal/operations-support.svelte.ts

@@ -1,104 +0,0 @@
-import { setDifference, type TimelineDate } from '$lib/utils/timeline-util';
-import { AssetOrder } from '@immich/sdk';
-
-import { SvelteSet } from 'svelte/reactivity';
-import { GroupInsertionCache } from '../group-insertion-cache.svelte';
-import { MonthGroup } from '../month-group.svelte';
-import type { TimelineManager } from '../timeline-manager.svelte';
-import type { AssetOperation, TimelineAsset } from '../types';
-import { updateGeometry } from './layout-support.svelte';
-import { getMonthGroupByDate } from './search-support.svelte';
-
-export function addAssetsToMonthGroups(
-  timelineManager: TimelineManager,
-  assets: TimelineAsset[],
-  options: { order: AssetOrder },
-) {
-  if (assets.length === 0) {
-    return;
-  }
-
-  const addContext = new GroupInsertionCache();
-  const updatedMonthGroups = new SvelteSet<MonthGroup>();
-  const monthCount = timelineManager.months.length;
-  for (const asset of assets) {
-    let month = getMonthGroupByDate(timelineManager, asset.localDateTime);
-
-    if (!month) {
-      month = new MonthGroup(timelineManager, asset.localDateTime, 1, options.order);
-      month.isLoaded = true;
-      timelineManager.months.push(month);
-    }
-
-    month.addTimelineAsset(asset, addContext);
-    updatedMonthGroups.add(month);
-  }
-
-  if (timelineManager.months.length !== monthCount) {
-    timelineManager.months.sort((a, b) => {
-      return a.yearMonth.year === b.yearMonth.year
-        ? b.yearMonth.month - a.yearMonth.month
-        : b.yearMonth.year - a.yearMonth.year;
-    });
-  }
-
-  for (const group of addContext.existingDayGroups) {
-    group.sortAssets(options.order);
-  }
-
-  for (const monthGroup of addContext.bucketsWithNewDayGroups) {
-    monthGroup.sortDayGroups();
-  }
-
-  for (const month of addContext.updatedBuckets) {
-    month.sortDayGroups();
-    updateGeometry(timelineManager, month, { invalidateHeight: true });
-  }
-  timelineManager.updateIntersections();
-}
-
-export function runAssetOperation(
-  timelineManager: TimelineManager,
-  ids: Set<string>,
-  operation: AssetOperation,
-  options: { order: AssetOrder },
-) {
-  if (ids.size === 0) {
-    return { processedIds: new SvelteSet(), unprocessedIds: ids, changedGeometry: false };
-  }
-
-  const changedMonthGroups = new SvelteSet<MonthGroup>();
-  let idsToProcess = new SvelteSet(ids);
-  const idsProcessed = new SvelteSet<string>();
-  const combinedMoveAssets: { asset: TimelineAsset; date: TimelineDate }[][] = [];
-  for (const month of timelineManager.months) {
-    if (idsToProcess.size > 0) {
-      const { moveAssets, processedIds, changedGeometry } = month.runAssetOperation(idsToProcess, operation);
-      if (moveAssets.length > 0) {
-        combinedMoveAssets.push(moveAssets);
-      }
-      idsToProcess = setDifference(idsToProcess, processedIds);
-      for (const id of processedIds) {
-        idsProcessed.add(id);
-      }
-      if (changedGeometry) {
-        changedMonthGroups.add(month);
-      }
-    }
-  }
-  if (combinedMoveAssets.length > 0) {
-    addAssetsToMonthGroups(
-      timelineManager,
-      combinedMoveAssets.flat().map((a) => a.asset),
-      options,
-    );
-  }
-  const changedGeometry = changedMonthGroups.size > 0;
-  for (const month of changedMonthGroups) {
-    updateGeometry(timelineManager, month, { invalidateHeight: true });
-  }
-  if (changedGeometry) {
-    timelineManager.updateIntersections();
-  }
-  return { unprocessedIds: idsToProcess, processedIds: idsProcessed, changedGeometry };
-}

web/src/lib/managers/timeline-manager/internal/websocket-support.svelte.ts

@@ -13,10 +13,10 @@ export class WebsocketSupport {
   #processPendingChanges = throttle(() => {
     const { add, update, remove } = this.#getPendingChangeBatches();
     if (add.length > 0) {
-      this.#timelineManager.addAssets(add);
+      this.#timelineManager.upsertAssets(add);
     }
     if (update.length > 0) {
-      this.#timelineManager.updateAssets(update);
+      this.#timelineManager.upsertAssets(update);
     }
     if (remove.length > 0) {
       this.#timelineManager.removeAssets(remove);

web/src/lib/managers/timeline-manager/month-group.svelte.ts

@@ -1,22 +1,26 @@
 import { AssetOrder, type TimeBucketAssetResponseDto } from '@immich/sdk';
 
-import { CancellableTask } from '$lib/utils/cancellable-task';
-import { handleError } from '$lib/utils/handle-error';
 import {
   formatGroupTitle,
+  formatGroupTitleFull,
   formatMonthGroupTitle,
   fromTimelinePlainDate,
   fromTimelinePlainDateTime,
   fromTimelinePlainYearMonth,
+  getSegmentIdentifier,
   getTimes,
   setDifference,
   type TimelineDateTime,
   type TimelineYearMonth,
 } from '$lib/utils/timeline-util';
 
-import { t } from 'svelte-i18n';
-import { get } from 'svelte/store';
+import { layoutMonthGroup, updateGeometry } from '$lib/managers/timeline-manager/internal/layout-support.svelte';
+import { loadFromTimeBuckets } from '$lib/managers/timeline-manager/internal/load-support.svelte';
 
+import {
+  PhotostreamSegment,
+  type SegmentIdentifier,
+} from '$lib/managers/photostream-manager/PhotostreamSegment.svelte';
 import { SvelteSet } from 'svelte/reactivity';
 import { DayGroup } from './day-group.svelte';
 import { GroupInsertionCache } from './group-insertion-cache.svelte';
@@ -24,71 +28,49 @@ import type { TimelineManager } from './timeline-manager.svelte';
 import type { AssetDescriptor, AssetOperation, Direction, MoveAsset, TimelineAsset } from './types';
 import { ViewerAsset } from './viewer-asset.svelte';
 
-export class MonthGroup {
-  #intersecting: boolean = $state(false);
-  actuallyIntersecting: boolean = $state(false);
-  isLoaded: boolean = $state(false);
+export class MonthGroup extends PhotostreamSegment {
   dayGroups: DayGroup[] = $state([]);
-  readonly timelineManager: TimelineManager;
 
-  #height: number = $state(0);
-  #top: number = $state(0);
-
-  #initialCount: number = 0;
   #sortOrder: AssetOrder = AssetOrder.Desc;
-  percent: number = $state(0);
-
-  assetsCount: number = $derived(
-    this.isLoaded
-      ? this.dayGroups.reduce((accumulator, g) => accumulator + g.viewerAssets.length, 0)
-      : this.#initialCount,
-  );
-  loader: CancellableTask | undefined;
-  isHeightActual: boolean = $state(false);
+  #yearMonth: TimelineYearMonth;
+  #identifier: SegmentIdentifier;
+  #timelineManager: TimelineManager;
 
   readonly monthGroupTitle: string;
-  readonly yearMonth: TimelineYearMonth;
 
   constructor(
-    store: TimelineManager,
+    timelineManager: TimelineManager,
     yearMonth: TimelineYearMonth,
     initialCount: number,
+    loaded: boolean,
     order: AssetOrder = AssetOrder.Desc,
   ) {
-    this.timelineManager = store;
-    this.#initialCount = initialCount;
+    super();
+    this.initialCount = initialCount;
+    this.#yearMonth = yearMonth;
+    this.#identifier = getSegmentIdentifier(yearMonth);
+    this.#timelineManager = timelineManager;
     this.#sortOrder = order;
-
-    this.yearMonth = yearMonth;
     this.monthGroupTitle = formatMonthGroupTitle(fromTimelinePlainYearMonth(yearMonth));
-
-    this.loader = new CancellableTask(
-      () => {
-        this.isLoaded = true;
-      },
-      () => {
-        this.dayGroups = [];
-        this.isLoaded = false;
-      },
-      this.#handleLoadError,
-    );
-  }
-
-  set intersecting(newValue: boolean) {
-    const old = this.#intersecting;
-    if (old === newValue) {
-      return;
-    }
-    this.#intersecting = newValue;
-    if (newValue) {
-      void this.timelineManager.loadMonthGroup(this.yearMonth);
-    } else {
-      this.cancel();
+    if (loaded) {
+      this.markLoaded();
     }
   }
 
-  get intersecting() {
-    return this.#intersecting;
+  get identifier() {
+    return this.#identifier;
+  }
+
+  get timelineManager() {
+    return this.#timelineManager;
+  }
+
+  get yearMonth() {
+    return this.#yearMonth;
+  }
+
+  fetch(signal: AbortSignal): Promise<void> {
+    return loadFromTimeBuckets(this.timelineManager, this, this.timelineManager.options, signal);
   }
 
   get lastDayGroup() {
@@ -99,9 +81,9 @@ export class MonthGroup {
     return this.dayGroups[0]?.getFirstAsset();
   }
 
-  getAssets() {
+  get viewerAssets() {
     // eslint-disable-next-line unicorn/no-array-reduce
-    return this.dayGroups.reduce((accumulator: TimelineAsset[], g: DayGroup) => accumulator.concat(g.getAssets()), []);
+    return this.dayGroups.reduce((accumulator: ViewerAsset[], g: DayGroup) => accumulator.concat(g.viewerAssets), []);
   }
 
   sortDayGroups() {
@@ -222,7 +204,8 @@ export class MonthGroup {
       addContext.setDayGroup(dayGroup, localDateTime);
     } else {
       const groupTitle = formatGroupTitle(fromTimelinePlainDate(localDateTime));
-      dayGroup = new DayGroup(this, this.dayGroups.length, localDateTime.day, groupTitle);
+      const groupTitleFull = formatGroupTitleFull(fromTimelinePlainDate(localDateTime));
+      dayGroup = new DayGroup(this, this.dayGroups.length, localDateTime.day, groupTitle, groupTitleFull);
       this.dayGroups.push(dayGroup);
       addContext.setDayGroup(dayGroup, localDateTime);
       addContext.newDayGroups.add(dayGroup);
@@ -242,67 +225,15 @@ export class MonthGroup {
     return this.getRandomDayGroup()?.getRandomAsset()?.asset;
   }
 
+  get id() {
+    return this.viewId;
+  }
+
   get viewId() {
     const { year, month } = this.yearMonth;
     return year + '-' + month;
   }
 
-  set height(height: number) {
-    if (this.#height === height) {
-      return;
-    }
-    const { timelineManager: store, percent } = this;
-    const index = store.months.indexOf(this);
-    const heightDelta = height - this.#height;
-    this.#height = height;
-    const prevMonthGroup = store.months[index - 1];
-    if (prevMonthGroup) {
-      const newTop = prevMonthGroup.#top + prevMonthGroup.#height;
-      if (this.#top !== newTop) {
-        this.#top = newTop;
-      }
-    }
-    for (let cursor = index + 1; cursor < store.months.length; cursor++) {
-      const monthGroup = this.timelineManager.months[cursor];
-      const newTop = monthGroup.#top + heightDelta;
-      if (monthGroup.#top !== newTop) {
-        monthGroup.#top = newTop;
-      }
-    }
-    if (store.topIntersectingMonthGroup) {
-      const currentIndex = store.months.indexOf(store.topIntersectingMonthGroup);
-      if (currentIndex > 0) {
-        if (index < currentIndex) {
-          store.scrollCompensation = {
-            heightDelta,
-            scrollTop: undefined,
-            monthGroup: this,
-          };
-        } else if (percent > 0) {
-          const top = this.top + height * percent;
-          store.scrollCompensation = {
-            heightDelta: undefined,
-            scrollTop: top,
-            monthGroup: this,
-          };
-        }
-      }
-    }
-  }
-
-  get height() {
-    return this.#height;
-  }
-
-  get top(): number {
-    return this.#top + this.timelineManager.topSectionHeight;
-  }
-
-  #handleLoadError(error: unknown) {
-    const _$t = get(t);
-    handleError(error, _$t('errors.failed_to_load_assets'));
-  }
-
   findDayGroupForAsset(asset: TimelineAsset) {
     for (const group of this.dayGroups) {
       if (group.viewerAssets.some((viewerAsset) => viewerAsset.id === asset.id)) {
@@ -316,7 +247,7 @@ export class MonthGroup {
   }
 
   findAssetAbsolutePosition(assetId: string) {
-    this.timelineManager.clearDeferredLayout(this);
+    this.#clearDeferredLayout();
     for (const group of this.dayGroups) {
       const viewerAsset = group.viewerAssets.find((viewAsset) => viewAsset.id === assetId);
       if (viewerAsset) {
@@ -374,4 +305,26 @@ export class MonthGroup {
   cancel() {
     this.loader?.cancel();
   }
+
+  layout(noDefer: boolean) {
+    layoutMonthGroup(this.timelineManager, this, noDefer);
+  }
+
+  #clearDeferredLayout() {
+    const hasDeferred = this.dayGroups.some((group) => group.deferredLayout);
+    if (hasDeferred) {
+      updateGeometry(this.timelineManager, this, { invalidateHeight: true, noDefer: true });
+      for (const group of this.dayGroups) {
+        group.deferredLayout = false;
+      }
+    }
+  }
+
+  updateIntersection({ intersecting, actuallyIntersecting }: { intersecting: boolean; actuallyIntersecting: boolean }) {
+    this.intersecting = intersecting;
+    this.actuallyIntersecting = actuallyIntersecting;
+    if (intersecting) {
+      this.#clearDeferredLayout();
+    }
+  }
 }

web/src/lib/managers/timeline-manager/timeline-manager.svelte.spec.ts

@@ -1,7 +1,7 @@
 import { sdkMock } from '$lib/__mocks__/sdk.mock';
 import { getMonthGroupByDate } from '$lib/managers/timeline-manager/internal/search-support.svelte';
 import { AbortError } from '$lib/utils';
-import { fromISODateTimeUTCToObject } from '$lib/utils/timeline-util';
+import { fromISODateTimeUTCToObject, getSegmentIdentifier } from '$lib/utils/timeline-util';
 import { type AssetResponseDto, type TimeBucketAssetResponseDto } from '@immich/sdk';
 import { timelineAssetFactory, toResponseDto } from '@test-data/factories/asset-factory';
 import { TimelineManager } from './timeline-manager.svelte';
@@ -92,7 +92,7 @@ describe('TimelineManager', () => {
     });
   });
 
-  describe('loadMonthGroup', () => {
+  describe('loadSegment', () => {
     let timelineManager: TimelineManager;
     const bucketAssets: Record<string, TimelineAsset[]> = {
       '2024-01-03T00:00:00.000Z': timelineAssetFactory.buildList(1).map((asset) =>
@@ -128,52 +128,52 @@ describe('TimelineManager', () => {
     });
 
     it('loads a month', async () => {
-      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.getAssets().length).toEqual(0);
-      await timelineManager.loadMonthGroup({ year: 2024, month: 1 });
+      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.assets.length).toEqual(0);
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
       expect(sdkMock.getTimeBucket).toBeCalledTimes(1);
-      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.getAssets().length).toEqual(3);
+      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.assets.length).toEqual(3);
     });
 
     it('ignores invalid months', async () => {
-      await timelineManager.loadMonthGroup({ year: 2023, month: 1 });
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2023, month: 1 }));
       expect(sdkMock.getTimeBucket).toBeCalledTimes(0);
     });
 
     it('cancels month loading', async () => {
       const month = getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })!;
-      void timelineManager.loadMonthGroup({ year: 2024, month: 1 });
+      void timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
       const abortSpy = vi.spyOn(month!.loader!.cancelToken!, 'abort');
       month?.cancel();
       expect(abortSpy).toBeCalledTimes(1);
-      await timelineManager.loadMonthGroup({ year: 2024, month: 1 });
-      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.getAssets().length).toEqual(3);
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
+      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.assets.length).toEqual(3);
     });
 
     it('prevents loading months multiple times', async () => {
       await Promise.all([
-        timelineManager.loadMonthGroup({ year: 2024, month: 1 }),
-        timelineManager.loadMonthGroup({ year: 2024, month: 1 }),
+        timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 })),
+        timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 })),
       ]);
       expect(sdkMock.getTimeBucket).toBeCalledTimes(1);
 
-      await timelineManager.loadMonthGroup({ year: 2024, month: 1 });
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
       expect(sdkMock.getTimeBucket).toBeCalledTimes(1);
     });
 
     it('allows loading a canceled month', async () => {
       const month = getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })!;
-      const loadPromise = timelineManager.loadMonthGroup({ year: 2024, month: 1 });
+      const loadPromise = timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
 
       month.cancel();
       await loadPromise;
-      expect(month?.getAssets().length).toEqual(0);
+      expect(month?.assets.length).toEqual(0);
 
-      await timelineManager.loadMonthGroup({ year: 2024, month: 1 });
-      expect(month!.getAssets().length).toEqual(3);
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
+      expect(month!.assets.length).toEqual(3);
     });
   });
 
-  describe('addAssets', () => {
+  describe('upsertAssets', () => {
     let timelineManager: TimelineManager;
 
     beforeEach(async () => {
@@ -194,11 +194,11 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-01-20T12:00:00.000Z'),
         }),
       );
-      timelineManager.addAssets([asset]);
+      timelineManager.upsertAssets([asset]);
 
       expect(timelineManager.months.length).toEqual(1);
       expect(timelineManager.assetCount).toEqual(1);
-      expect(timelineManager.months[0].getAssets().length).toEqual(1);
+      expect(timelineManager.months[0].assets.length).toEqual(1);
       expect(timelineManager.months[0].yearMonth.year).toEqual(2024);
       expect(timelineManager.months[0].yearMonth.month).toEqual(1);
       expect(timelineManager.months[0].getFirstAsset().id).toEqual(asset.id);
@@ -210,12 +210,12 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-01-20T12:00:00.000Z'),
         })
         .map((asset) => deriveLocalDateTimeFromFileCreatedAt(asset));
-      timelineManager.addAssets([assetOne]);
-      timelineManager.addAssets([assetTwo]);
+      timelineManager.upsertAssets([assetOne]);
+      timelineManager.upsertAssets([assetTwo]);
 
       expect(timelineManager.months.length).toEqual(1);
       expect(timelineManager.assetCount).toEqual(2);
-      expect(timelineManager.months[0].getAssets().length).toEqual(2);
+      expect(timelineManager.months[0].assets.length).toEqual(2);
       expect(timelineManager.months[0].yearMonth.year).toEqual(2024);
       expect(timelineManager.months[0].yearMonth.month).toEqual(1);
     });
@@ -236,14 +236,14 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-01-16T12:00:00.000Z'),
         }),
       );
-      timelineManager.addAssets([assetOne, assetTwo, assetThree]);
+      timelineManager.upsertAssets([assetOne, assetTwo, assetThree]);
 
       const month = getMonthGroupByDate(timelineManager, { year: 2024, month: 1 });
       expect(month).not.toBeNull();
-      expect(month?.getAssets().length).toEqual(3);
-      expect(month?.getAssets()[0].id).toEqual(assetOne.id);
-      expect(month?.getAssets()[1].id).toEqual(assetThree.id);
-      expect(month?.getAssets()[2].id).toEqual(assetTwo.id);
+      expect(month?.assets.length).toEqual(3);
+      expect(month?.assets[0].id).toEqual(assetOne.id);
+      expect(month?.assets[1].id).toEqual(assetThree.id);
+      expect(month?.assets[2].id).toEqual(assetTwo.id);
     });
 
     it('orders months by descending date', () => {
@@ -262,7 +262,7 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2023-01-20T12:00:00.000Z'),
         }),
       );
-      timelineManager.addAssets([assetOne, assetTwo, assetThree]);
+      timelineManager.upsertAssets([assetOne, assetTwo, assetThree]);
 
       expect(timelineManager.months.length).toEqual(3);
       expect(timelineManager.months[0].yearMonth.year).toEqual(2024);
@@ -276,11 +276,11 @@ describe('TimelineManager', () => {
     });
 
     it('updates existing asset', () => {
-      const updateAssetsSpy = vi.spyOn(timelineManager, 'updateAssets');
+      const updateAssetsSpy = vi.spyOn(timelineManager, 'upsertAssets');
       const asset = deriveLocalDateTimeFromFileCreatedAt(timelineAssetFactory.build());
-      timelineManager.addAssets([asset]);
+      timelineManager.upsertAssets([asset]);
 
-      timelineManager.addAssets([asset]);
+      timelineManager.upsertAssets([asset]);
       expect(updateAssetsSpy).toBeCalledWith([asset]);
       expect(timelineManager.assetCount).toEqual(1);
     });
@@ -292,7 +292,7 @@ describe('TimelineManager', () => {
 
       const timelineManager = new TimelineManager();
       await timelineManager.updateOptions({ isTrashed: true });
-      timelineManager.addAssets([asset, trashedAsset]);
+      timelineManager.upsertAssets([asset, trashedAsset]);
       expect(await getAssets(timelineManager)).toEqual([trashedAsset]);
     });
   });
@@ -307,22 +307,15 @@ describe('TimelineManager', () => {
       await timelineManager.updateViewport({ width: 1588, height: 1000 });
     });
 
-    it('ignores non-existing assets', () => {
-      timelineManager.updateAssets([deriveLocalDateTimeFromFileCreatedAt(timelineAssetFactory.build())]);
-
-      expect(timelineManager.months.length).toEqual(0);
-      expect(timelineManager.assetCount).toEqual(0);
-    });
-
     it('updates an asset', () => {
       const asset = deriveLocalDateTimeFromFileCreatedAt(timelineAssetFactory.build({ isFavorite: false }));
       const updatedAsset = { ...asset, isFavorite: true };
 
-      timelineManager.addAssets([asset]);
+      timelineManager.upsertAssets([asset]);
       expect(timelineManager.assetCount).toEqual(1);
       expect(timelineManager.months[0].getFirstAsset().isFavorite).toEqual(false);
 
-      timelineManager.updateAssets([updatedAsset]);
+      timelineManager.upsertAssets([updatedAsset]);
       expect(timelineManager.assetCount).toEqual(1);
       expect(timelineManager.months[0].getFirstAsset().isFavorite).toEqual(true);
     });
@@ -338,17 +331,17 @@ describe('TimelineManager', () => {
         fileCreatedAt: fromISODateTimeUTCToObject('2024-03-20T12:00:00.000Z'),
       });
 
-      timelineManager.addAssets([asset]);
+      timelineManager.upsertAssets([asset]);
       expect(timelineManager.months.length).toEqual(1);
       expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })).not.toBeUndefined();
-      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.getAssets().length).toEqual(1);
+      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.assets.length).toEqual(1);
 
-      timelineManager.updateAssets([updatedAsset]);
+      timelineManager.upsertAssets([updatedAsset]);
       expect(timelineManager.months.length).toEqual(2);
       expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })).not.toBeUndefined();
-      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.getAssets().length).toEqual(0);
+      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 1 })?.assets.length).toEqual(0);
       expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 3 })).not.toBeUndefined();
-      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 3 })?.getAssets().length).toEqual(1);
+      expect(getMonthGroupByDate(timelineManager, { year: 2024, month: 3 })?.assets.length).toEqual(1);
     });
   });
 
@@ -363,7 +356,7 @@ describe('TimelineManager', () => {
     });
 
     it('ignores invalid IDs', () => {
-      timelineManager.addAssets(
+      timelineManager.upsertAssets(
         timelineAssetFactory
           .buildList(2, {
             fileCreatedAt: fromISODateTimeUTCToObject('2024-01-20T12:00:00.000Z'),
@@ -374,7 +367,7 @@ describe('TimelineManager', () => {
 
       expect(timelineManager.assetCount).toEqual(2);
       expect(timelineManager.months.length).toEqual(1);
-      expect(timelineManager.months[0].getAssets().length).toEqual(2);
+      expect(timelineManager.months[0].assets.length).toEqual(2);
     });
 
     it('removes asset from month', () => {
@@ -383,12 +376,12 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-01-20T12:00:00.000Z'),
         })
         .map((asset) => deriveLocalDateTimeFromFileCreatedAt(asset));
-      timelineManager.addAssets([assetOne, assetTwo]);
+      timelineManager.upsertAssets([assetOne, assetTwo]);
       timelineManager.removeAssets([assetOne.id]);
 
       expect(timelineManager.assetCount).toEqual(1);
       expect(timelineManager.months.length).toEqual(1);
-      expect(timelineManager.months[0].getAssets().length).toEqual(1);
+      expect(timelineManager.months[0].assets.length).toEqual(1);
     });
 
     it('does not remove month when empty', () => {
@@ -397,7 +390,7 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-01-20T12:00:00.000Z'),
         })
         .map((asset) => deriveLocalDateTimeFromFileCreatedAt(asset));
-      timelineManager.addAssets(assets);
+      timelineManager.upsertAssets(assets);
       timelineManager.removeAssets(assets.map((asset) => asset.id));
 
       expect(timelineManager.assetCount).toEqual(0);
@@ -429,7 +422,7 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-01-15T12:00:00.000Z'),
         }),
       );
-      timelineManager.addAssets([assetOne, assetTwo]);
+      timelineManager.upsertAssets([assetOne, assetTwo]);
       expect(timelineManager.getFirstAsset()).toEqual(assetOne);
     });
   });
@@ -477,45 +470,45 @@ describe('TimelineManager', () => {
     });
 
     it('returns previous assetId', async () => {
-      await timelineManager.loadMonthGroup({ year: 2024, month: 1 });
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
       const month = getMonthGroupByDate(timelineManager, { year: 2024, month: 1 });
 
-      const a = month!.getAssets()[0];
-      const b = month!.getAssets()[1];
+      const a = month!.assets[0];
+      const b = month!.assets[1];
       const previous = await timelineManager.getLaterAsset(b);
       expect(previous).toEqual(a);
     });
 
     it('returns previous assetId spanning multiple months', async () => {
-      await timelineManager.loadMonthGroup({ year: 2024, month: 2 });
-      await timelineManager.loadMonthGroup({ year: 2024, month: 3 });
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 2 }));
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 3 }));
 
       const month = getMonthGroupByDate(timelineManager, { year: 2024, month: 2 });
       const previousMonth = getMonthGroupByDate(timelineManager, { year: 2024, month: 3 });
-      const a = month!.getAssets()[0];
-      const b = previousMonth!.getAssets()[0];
+      const a = month!.assets[0];
+      const b = previousMonth!.assets[0];
       const previous = await timelineManager.getLaterAsset(a);
       expect(previous).toEqual(b);
     });
 
     it('loads previous month', async () => {
-      await timelineManager.loadMonthGroup({ year: 2024, month: 2 });
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 2 }));
       const month = getMonthGroupByDate(timelineManager, { year: 2024, month: 2 });
       const previousMonth = getMonthGroupByDate(timelineManager, { year: 2024, month: 3 });
       const a = month!.getFirstAsset();
       const b = previousMonth!.getFirstAsset();
-      const loadMonthGroupSpy = vi.spyOn(month!.loader!, 'execute');
+      const loadSegmentSpy = vi.spyOn(month!.loader!, 'execute');
       const previousMonthSpy = vi.spyOn(previousMonth!.loader!, 'execute');
       const previous = await timelineManager.getLaterAsset(a);
       expect(previous).toEqual(b);
-      expect(loadMonthGroupSpy).toBeCalledTimes(0);
+      expect(loadSegmentSpy).toBeCalledTimes(0);
       expect(previousMonthSpy).toBeCalledTimes(0);
     });
 
     it('skips removed assets', async () => {
-      await timelineManager.loadMonthGroup({ year: 2024, month: 1 });
-      await timelineManager.loadMonthGroup({ year: 2024, month: 2 });
-      await timelineManager.loadMonthGroup({ year: 2024, month: 3 });
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 1 }));
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 2 }));
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 3 }));
 
       const [assetOne, assetTwo, assetThree] = await getAssets(timelineManager);
       timelineManager.removeAssets([assetTwo.id]);
@@ -523,7 +516,7 @@ describe('TimelineManager', () => {
     });
 
     it('returns null when no more assets', async () => {
-      await timelineManager.loadMonthGroup({ year: 2024, month: 3 });
+      await timelineManager.loadSegment(getSegmentIdentifier({ year: 2024, month: 3 }));
       expect(await timelineManager.getLaterAsset(timelineManager.months[0].getFirstAsset())).toBeUndefined();
     });
   });
@@ -554,7 +547,7 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-02-15T12:00:00.000Z'),
         }),
       );
-      timelineManager.addAssets([assetOne, assetTwo]);
+      timelineManager.upsertAssets([assetOne, assetTwo]);
 
       expect(timelineManager.getMonthGroupByAssetId(assetTwo.id)?.yearMonth.year).toEqual(2024);
       expect(timelineManager.getMonthGroupByAssetId(assetTwo.id)?.yearMonth.month).toEqual(2);
@@ -573,7 +566,7 @@ describe('TimelineManager', () => {
           fileCreatedAt: fromISODateTimeUTCToObject('2024-02-15T12:00:00.000Z'),
         }),
       );
-      timelineManager.addAssets([assetOne, assetTwo]);
+      timelineManager.upsertAssets([assetOne, assetTwo]);
 
       timelineManager.removeAssets([assetTwo.id]);
       expect(timelineManager.getMonthGroupByAssetId(assetOne.id)?.yearMonth.year).toEqual(2024);

web/src/lib/managers/timeline-manager/timeline-manager.svelte.ts

@@ -3,18 +3,19 @@ import { AssetOrder, getAssetInfo, getTimeBuckets } from '@immich/sdk';
 import { authManager } from '$lib/managers/auth-manager.svelte';
 
 import { CancellableTask } from '$lib/utils/cancellable-task';
-import { toTimelineAsset, type TimelineDateTime, type TimelineYearMonth } from '$lib/utils/timeline-util';
-
-import { clamp, debounce, isEqual } from 'lodash-es';
-import { SvelteDate, SvelteMap, SvelteSet } from 'svelte/reactivity';
-
-import { updateIntersectionMonthGroup } from '$lib/managers/timeline-manager/internal/intersection-support.svelte';
-import { updateGeometry } from '$lib/managers/timeline-manager/internal/layout-support.svelte';
-import { loadFromTimeBuckets } from '$lib/managers/timeline-manager/internal/load-support.svelte';
 import {
-  addAssetsToMonthGroups,
-  runAssetOperation,
-} from '$lib/managers/timeline-manager/internal/operations-support.svelte';
+  getSegmentIdentifier,
+  toTimelineAsset,
+  type TimelineDateTime,
+  type TimelineYearMonth,
+} from '$lib/utils/timeline-util';
+
+import { isEqual } from 'lodash-es';
+import { SvelteDate, SvelteSet } from 'svelte/reactivity';
+
+import { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
+import { GroupInsertionCache } from '$lib/managers/timeline-manager/group-insertion-cache.svelte';
+import { updateGeometry } from '$lib/managers/timeline-manager/internal/layout-support.svelte';
 import {
   findMonthGroupForAsset as findMonthGroupForAssetUtil,
   findMonthGroupForDate,
@@ -24,37 +25,15 @@ import {
 } from '$lib/managers/timeline-manager/internal/search-support.svelte';
 import { WebsocketSupport } from '$lib/managers/timeline-manager/internal/websocket-support.svelte';
 import { DayGroup } from './day-group.svelte';
-import { isMismatched, updateObject } from './internal/utils.svelte';
+import { isMismatched } from './internal/utils.svelte';
 import { MonthGroup } from './month-group.svelte';
-import type {
-  AssetDescriptor,
-  AssetOperation,
-  Direction,
-  ScrubberMonth,
-  TimelineAsset,
-  TimelineManagerLayoutOptions,
-  TimelineManagerOptions,
-  Viewport,
-} from './types';
-
-export class TimelineManager {
-  isInitialized = $state(false);
-  months: MonthGroup[] = $state([]);
-  topSectionHeight = $state(0);
-  timelineHeight = $derived(this.months.reduce((accumulator, b) => accumulator + b.height, 0) + this.topSectionHeight);
-  assetCount = $derived(this.months.reduce((accumulator, b) => accumulator + b.assetsCount, 0));
+import type { AssetDescriptor, Direction, ScrubberMonth, TimelineAsset, TimelineManagerOptions } from './types';
 
+export class TimelineManager extends PhotostreamManager {
   albumAssets: Set<string> = new SvelteSet();
-
   scrubberMonths: ScrubberMonth[] = $state([]);
   scrubberTimelineHeight: number = $state(0);
-
-  topIntersectingMonthGroup: MonthGroup | undefined = $state();
-
-  visibleWindow = $derived.by(() => ({
-    top: this.#scrollTop,
-    bottom: this.#scrollTop + this.viewportHeight,
-  }));
+  #months: MonthGroup[] = $state([]);
 
   initTask = new CancellableTask(
     () => {
@@ -72,121 +51,16 @@ export class TimelineManager {
   );
 
   static #INIT_OPTIONS = {};
-  #viewportHeight = $state(0);
-  #viewportWidth = $state(0);
-  #scrollTop = $state(0);
+
   #websocketSupport: WebsocketSupport | undefined;
-
-  #rowHeight = $state(235);
-  #headerHeight = $state(48);
-  #gap = $state(12);
-
   #options: TimelineManagerOptions = TimelineManager.#INIT_OPTIONS;
 
-  #scrolling = $state(false);
-  #suspendTransitions = $state(false);
-  #resetScrolling = debounce(() => (this.#scrolling = false), 1000);
-  #resetSuspendTransitions = debounce(() => (this.suspendTransitions = false), 1000);
-  scrollCompensation: {
-    heightDelta: number | undefined;
-    scrollTop: number | undefined;
-    monthGroup: MonthGroup | undefined;
-  } = $state({
-    heightDelta: 0,
-    scrollTop: 0,
-    monthGroup: undefined,
-  });
-
-  constructor() {}
-
-  setLayoutOptions({ headerHeight = 48, rowHeight = 235, gap = 12 }: TimelineManagerLayoutOptions) {
-    let changed = false;
-    changed ||= this.#setHeaderHeight(headerHeight);
-    changed ||= this.#setGap(gap);
-    changed ||= this.#setRowHeight(rowHeight);
-    if (changed) {
-      this.refreshLayout();
-    }
+  get months() {
+    return this.#months;
   }
 
-  #setHeaderHeight(value: number) {
-    if (this.#headerHeight == value) {
-      return false;
-    }
-    this.#headerHeight = value;
-    return true;
-  }
-
-  get headerHeight() {
-    return this.#headerHeight;
-  }
-
-  #setGap(value: number) {
-    if (this.#gap == value) {
-      return false;
-    }
-    this.#gap = value;
-    return true;
-  }
-
-  get gap() {
-    return this.#gap;
-  }
-
-  #setRowHeight(value: number) {
-    if (this.#rowHeight == value) {
-      return false;
-    }
-    this.#rowHeight = value;
-    return true;
-  }
-
-  get rowHeight() {
-    return this.#rowHeight;
-  }
-
-  set scrolling(value: boolean) {
-    this.#scrolling = value;
-    if (value) {
-      this.suspendTransitions = true;
-      this.#resetScrolling();
-    }
-  }
-
-  get scrolling() {
-    return this.#scrolling;
-  }
-
-  set suspendTransitions(value: boolean) {
-    this.#suspendTransitions = value;
-    if (value) {
-      this.#resetSuspendTransitions();
-    }
-  }
-
-  get suspendTransitions() {
-    return this.#suspendTransitions;
-  }
-
-  set viewportWidth(value: number) {
-    const changed = value !== this.#viewportWidth;
-    this.#viewportWidth = value;
-    this.suspendTransitions = true;
-    void this.#updateViewportGeometry(changed);
-  }
-
-  get viewportWidth() {
-    return this.#viewportWidth;
-  }
-
-  set viewportHeight(value: number) {
-    this.#viewportHeight = value;
-    this.#suspendTransitions = true;
-    void this.#updateViewportGeometry(false);
-  }
-
-  get viewportHeight() {
-    return this.#viewportHeight;
+  get options() {
+    return this.#options;
   }
 
   async *assetsIterator(options?: {
@@ -198,7 +72,7 @@ export class TimelineManager {
     const direction = options?.direction ?? 'earlier';
     let { startDayGroup, startAsset } = options ?? {};
     for (const monthGroup of this.monthGroupIterator({ direction, startMonthGroup: options?.startMonthGroup })) {
-      await this.loadMonthGroup(monthGroup.yearMonth, { cancelable: false });
+      await this.loadSegment(monthGroup.identifier, { cancelable: false });
       yield* monthGroup.assetsIterator({ startDayGroup, startAsset, direction });
       startDayGroup = startAsset = undefined;
     }
@@ -234,75 +108,24 @@ export class TimelineManager {
     this.#websocketSupport = undefined;
   }
 
-  updateSlidingWindow(scrollTop: number) {
-    if (this.#scrollTop !== scrollTop) {
-      this.#scrollTop = scrollTop;
-      this.updateIntersections();
-    }
-  }
-
-  clearScrollCompensation() {
-    this.scrollCompensation = {
-      heightDelta: undefined,
-      scrollTop: undefined,
-      monthGroup: undefined,
-    };
-  }
-
-  updateIntersections() {
-    if (!this.isInitialized || this.visibleWindow.bottom === this.visibleWindow.top) {
-      return;
-    }
-    let topIntersectingMonthGroup = undefined;
-    for (const month of this.months) {
-      updateIntersectionMonthGroup(this, month);
-      if (!topIntersectingMonthGroup && month.actuallyIntersecting) {
-        topIntersectingMonthGroup = month;
-      }
-    }
-    if (topIntersectingMonthGroup !== undefined && this.topIntersectingMonthGroup !== topIntersectingMonthGroup) {
-      this.topIntersectingMonthGroup = topIntersectingMonthGroup;
-    }
-    for (const month of this.months) {
-      if (month === this.topIntersectingMonthGroup) {
-        this.topIntersectingMonthGroup.percent = clamp(
-          (this.visibleWindow.top - this.topIntersectingMonthGroup.top) / this.topIntersectingMonthGroup.height,
-          0,
-          1,
-        );
-      } else {
-        month.percent = 0;
-      }
-    }
-  }
-
-  clearDeferredLayout(month: MonthGroup) {
-    const hasDeferred = month.dayGroups.some((group) => group.deferredLayout);
-    if (hasDeferred) {
-      updateGeometry(this, month, { invalidateHeight: true, noDefer: true });
-      for (const group of month.dayGroups) {
-        group.deferredLayout = false;
-      }
-    }
-  }
-
   async #initializeMonthGroups() {
     const timebuckets = await getTimeBuckets({
       ...authManager.params,
       ...this.#options,
     });
 
-    this.months = timebuckets.map((timeBucket) => {
+    this.#months = timebuckets.map((timeBucket) => {
       const date = new SvelteDate(timeBucket.timeBucket);
       return new MonthGroup(
         this,
         { year: date.getUTCFullYear(), month: date.getUTCMonth() + 1 },
         timeBucket.count,
+        false,
         this.#options.order,
       );
     });
     this.albumAssets.clear();
-    this.#updateViewportGeometry(false);
+    this.updateViewportGeometry(false);
   }
 
   async updateOptions(options: TimelineManagerOptions) {
@@ -313,16 +136,16 @@ export class TimelineManager {
       return;
     }
     await this.initTask.reset();
-    await this.#init(options);
-    this.#updateViewportGeometry(false);
+    this.#options = options;
+    await this.init();
+    this.updateViewportGeometry(false);
   }
 
-  async #init(options: TimelineManagerOptions) {
+  async init() {
     this.isInitialized = false;
-    this.months = [];
+    this.#months = [];
     this.albumAssets.clear();
     await this.initTask.execute(async () => {
-      this.#options = options;
       await this.#initializeMonthGroups();
     }, true);
   }
@@ -332,36 +155,8 @@ export class TimelineManager {
     this.isInitialized = false;
   }
 
-  async updateViewport(viewport: Viewport) {
-    if (viewport.height === 0 && viewport.width === 0) {
-      return;
-    }
-
-    if (this.viewportHeight === viewport.height && this.viewportWidth === viewport.width) {
-      return;
-    }
-
-    if (!this.initTask.executed) {
-      await (this.initTask.loading ? this.initTask.waitUntilCompletion() : this.#init(this.#options));
-    }
-
-    const changedWidth = viewport.width !== this.viewportWidth;
-    this.viewportHeight = viewport.height;
-    this.viewportWidth = viewport.width;
-    this.#updateViewportGeometry(changedWidth);
-  }
-
-  #updateViewportGeometry(changedWidth: boolean) {
-    if (!this.isInitialized) {
-      return;
-    }
-    if (this.viewportWidth === 0 || this.viewportHeight === 0) {
-      return;
-    }
-    for (const month of this.months) {
-      updateGeometry(this, month, { invalidateHeight: changedWidth });
-    }
-    this.updateIntersections();
+  updateViewportGeometry(changedWidth: boolean) {
+    super.updateViewportGeometry(changedWidth);
     this.#createScrubberMonths();
   }
 
@@ -376,45 +171,6 @@ export class TimelineManager {
     this.scrubberTimelineHeight = this.timelineHeight;
   }
 
-  createLayoutOptions() {
-    const viewportWidth = this.viewportWidth;
-
-    return {
-      spacing: 2,
-      heightTolerance: 0.15,
-      rowHeight: this.#rowHeight,
-      rowWidth: Math.floor(viewportWidth),
-    };
-  }
-
-  async loadMonthGroup(yearMonth: TimelineYearMonth, options?: { cancelable: boolean }): Promise<void> {
-    let cancelable = true;
-    if (options) {
-      cancelable = options.cancelable;
-    }
-    const monthGroup = getMonthGroupByDate(this, yearMonth);
-    if (!monthGroup) {
-      return;
-    }
-
-    if (monthGroup.loader?.executed) {
-      return;
-    }
-
-    const result = await monthGroup.loader?.execute(async (signal: AbortSignal) => {
-      await loadFromTimeBuckets(this, monthGroup, this.#options, signal);
-    }, cancelable);
-    if (result === 'LOADED') {
-      updateIntersectionMonthGroup(this, monthGroup);
-    }
-  }
-
-  addAssets(assets: TimelineAsset[]) {
-    const assetsToUpdate = assets.filter((asset) => !this.isExcluded(asset));
-    const notUpdated = this.updateAssets(assetsToUpdate);
-    addAssetsToMonthGroups(this, [...notUpdated], { order: this.#options.order ?? AssetOrder.Desc });
-  }
-
   async findMonthGroupForAsset(id: string) {
     if (!this.isInitialized) {
       await this.initTask.waitUntilCompletion();
@@ -442,7 +198,7 @@ export class TimelineManager {
   }
 
   async #loadMonthGroupAtTime(yearMonth: TimelineYearMonth, options?: { cancelable: boolean }) {
-    await this.loadMonthGroup(yearMonth, options);
+    await this.loadSegment(getSegmentIdentifier(yearMonth), options);
     return getMonthGroupByDate(this, yearMonth);
   }
 
@@ -454,7 +210,7 @@ export class TimelineManager {
   async getRandomMonthGroup() {
     const random = Math.floor(Math.random() * this.months.length);
     const month = this.months[random];
-    await this.loadMonthGroup(month.yearMonth, { cancelable: false });
+    await this.loadSegment(getSegmentIdentifier(month.yearMonth), { cancelable: false });
     return month;
   }
 
@@ -463,40 +219,6 @@ export class TimelineManager {
     return month?.getRandomAsset();
   }
 
-  updateAssetOperation(ids: string[], operation: AssetOperation) {
-    runAssetOperation(this, new SvelteSet(ids), operation, { order: this.#options.order ?? AssetOrder.Desc });
-  }
-
-  updateAssets(assets: TimelineAsset[]) {
-    const lookup = new SvelteMap<string, TimelineAsset>(assets.map((asset) => [asset.id, asset]));
-    const { unprocessedIds } = runAssetOperation(
-      this,
-      new SvelteSet(lookup.keys()),
-      (asset) => {
-        updateObject(asset, lookup.get(asset.id));
-        return { remove: false };
-      },
-      { order: this.#options.order ?? AssetOrder.Desc },
-    );
-    const result: TimelineAsset[] = [];
-    for (const id of unprocessedIds.values()) {
-      result.push(lookup.get(id)!);
-    }
-    return result;
-  }
-
-  removeAssets(ids: string[]) {
-    const { unprocessedIds } = runAssetOperation(
-      this,
-      new SvelteSet(ids),
-      () => {
-        return { remove: true };
-      },
-      { order: this.#options.order ?? AssetOrder.Desc },
-    );
-    return [...unprocessedIds];
-  }
-
   refreshLayout() {
     for (const month of this.months) {
       updateGeometry(this, month, { invalidateHeight: true });
@@ -527,7 +249,7 @@ export class TimelineManager {
     if (!monthGroup) {
       return;
     }
-    await this.loadMonthGroup(dateTime, { cancelable: false });
+    await this.loadSegment(getSegmentIdentifier(dateTime), { cancelable: false });
     const asset = monthGroup.findClosest(dateTime);
     if (asset) {
       return asset;
@@ -552,4 +274,42 @@ export class TimelineManager {
   getAssetOrder() {
     return this.#options.order ?? AssetOrder.Desc;
   }
+
+  protected createUpsertContext(): unknown {
+    return new GroupInsertionCache();
+  }
+
+  protected upsertAssetIntoSegment(asset: TimelineAsset, context: GroupInsertionCache): void {
+    let month = getMonthGroupByDate(this, asset.localDateTime);
+
+    if (!month) {
+      month = new MonthGroup(this, asset.localDateTime, 1, true, this.#options.order);
+      this.months.push(month);
+    }
+
+    month.addTimelineAsset(asset, context);
+  }
+
+  protected postCreateSegments(): void {
+    this.months.sort((a, b) => {
+      return a.yearMonth.year === b.yearMonth.year
+        ? b.yearMonth.month - a.yearMonth.month
+        : b.yearMonth.year - a.yearMonth.year;
+    });
+  }
+
+  protected postUpsert(context: GroupInsertionCache): void {
+    for (const group of context.existingDayGroups) {
+      group.sortAssets(this.#options.order);
+    }
+
+    for (const monthGroup of context.bucketsWithNewDayGroups) {
+      monthGroup.sortDayGroups();
+    }
+
+    for (const month of context.updatedBuckets) {
+      month.sortDayGroups();
+      updateGeometry(this, month, { invalidateHeight: true });
+    }
+  }
 }

web/src/lib/managers/timeline-manager/types.ts

@@ -35,7 +35,7 @@ export type TimelineAsset = {
   longitude?: number | null;
 };
 
-export type AssetOperation = (asset: TimelineAsset) => { remove: boolean };
+export type AssetOperation = (asset: TimelineAsset) => { remove: boolean } | unknown;
 
 export type MoveAsset = { asset: TimelineAsset; date: TimelineDate };
 

web/src/lib/utils/actions.ts

@@ -21,15 +21,15 @@ export type OnSetVisibility = (ids: string[]) => void;
 
 export const deleteAssets = async (
   force: boolean,
-  onAssetDelete: OnDelete,
+  onAssetDelete: OnDelete | undefined,
   assets: TimelineAsset[],
-  onUndoDelete: OnUndoDelete | undefined = undefined,
+  onUndoDelete: OnUndoDelete | undefined,
 ) => {
   const $t = get(t);
   try {
     const ids = assets.map((a) => a.id);
     await deleteBulk({ assetBulkDeleteDto: { ids, force } });
-    onAssetDelete(ids);
+    onAssetDelete?.(ids);
 
     notificationController.show({
       message: force
@@ -98,5 +98,5 @@ export function updateUnstackedAssetInTimeline(timelineManager: TimelineManager,
     },
   );
 
-  timelineManager.addAssets(assets);
+  timelineManager.upsertAssets(assets);
 }

web/src/lib/utils/asset-utils.ts

@@ -513,7 +513,7 @@ export const selectAllAssets = async (timelineManager: TimelineManager, assetInt
 
   try {
     for (const monthGroup of timelineManager.months) {
-      await timelineManager.loadMonthGroup(monthGroup.yearMonth);
+      await timelineManager.loadSegment(monthGroup.identifier);
 
       if (!get(isSelectingAllAssets)) {
         assetInteraction.clearMultiselect();

web/src/lib/utils/timeline-util.ts

@@ -1,3 +1,4 @@
+import type { MonthGroup } from '$lib/managers/timeline-manager/month-group.svelte';
 import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
 import { locale } from '$lib/stores/preferences.store';
 import { getAssetRatio } from '$lib/utils/asset-utils';
@@ -151,6 +152,14 @@ export function formatGroupTitle(_date: DateTime): string {
   return getDateLocaleString(date, { locale: get(locale) });
 }
 
+export const formatGroupTitleFull = (_date: DateTime): string => {
+  if (!_date.isValid) {
+    return _date.toString();
+  }
+  const date = _date as DateTime<true>;
+  return getDateLocaleString(date);
+};
+
 export const getDateLocaleString = (date: DateTime, opts?: LocaleOptions): string =>
   date.toLocaleString(DateTime.DATE_MED_WITH_WEEKDAY, opts);
 
@@ -234,3 +243,11 @@ export function setDifference<T>(setA: Set<T>, setB: Set<T>): SvelteSet<T> {
   }
   return result;
 }
+
+export const getSegmentIdentifier = (yearMonth: TimelineYearMonth | TimelineDateTime) => ({
+  matches(segment: MonthGroup) {
+    return (
+      segment.yearMonth && segment.yearMonth.year === yearMonth.year && segment.yearMonth.month === yearMonth.month
+    );
+  },
+});

web/src/routes/(user)/albums/[albumId=id]/[[photos=photos]]/[[assetId=id]]/+page.svelte

@@ -34,7 +34,6 @@
   import { AlbumPageViewMode, AppRoute } from '$lib/constants';
   import { activityManager } from '$lib/managers/activity-manager.svelte';
   import { TimelineManager } from '$lib/managers/timeline-manager/timeline-manager.svelte';
-  import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
   import AlbumOptionsModal from '$lib/modals/AlbumOptionsModal.svelte';
   import AlbumShareModal from '$lib/modals/AlbumShareModal.svelte';
   import AlbumUsersModal from '$lib/modals/AlbumUsersModal.svelte';
@@ -262,18 +261,15 @@
     }
   };
 
-  const handleSetVisibility = (assetIds: string[]) => {
-    timelineManager.removeAssets(assetIds);
+  const handleSetVisibility = () => {
     assetInteraction.clearMultiselect();
   };
 
-  const handleRemoveAssets = async (assetIds: string[]) => {
-    timelineManager.removeAssets(assetIds);
+  const handleRemoveAssets = async () => {
     await refreshAlbum();
   };
 
-  const handleUndoRemoveAssets = async (assets: TimelineAsset[]) => {
-    timelineManager.addAssets(assets);
+  const handleUndoRemoveAssets = async () => {
     await refreshAlbum();
   };
 
@@ -572,14 +568,7 @@
           <AddToAlbum shared />
         </ButtonContextMenu>
         {#if assetInteraction.isAllUserOwned}
-          <FavoriteAction
-            removeFavorite={assetInteraction.isAllFavorite}
-            onFavorite={(ids, isFavorite) =>
-              timelineManager.updateAssetOperation(ids, (asset) => {
-                asset.isFavorite = isFavorite;
-                return { remove: false };
-              })}
-          ></FavoriteAction>
+          <FavoriteAction removeFavorite={assetInteraction.isAllFavorite} manager={timelineManager}></FavoriteAction>
         {/if}
         <ButtonContextMenu icon={mdiDotsVertical} title={$t('menu')} offset={{ x: 175, y: 25 }}>
           <DownloadAction menuItem filename="{album.albumName}.zip" />
@@ -594,7 +583,7 @@
                 onClick={() => updateThumbnailUsingCurrentSelection()}
               />
             {/if}
-            <ArchiveAction menuItem unarchive={assetInteraction.isAllArchived} />
+            <ArchiveAction menuItem unarchive={assetInteraction.isAllArchived} manager={timelineManager} />
             <SetVisibilityAction menuItem onVisibilitySet={handleSetVisibility} />
           {/if}
 
@@ -606,7 +595,12 @@
             <RemoveFromAlbum menuItem bind:album onRemove={handleRemoveAssets} />
           {/if}
           {#if assetInteraction.isAllUserOwned}
-            <DeleteAssets menuItem onAssetDelete={handleRemoveAssets} onUndoDelete={handleUndoRemoveAssets} />
+            <DeleteAssets
+              menuItem
+              onAssetDelete={handleRemoveAssets}
+              onUndoDelete={handleUndoRemoveAssets}
+              manager={timelineManager}
+            />
           {/if}
         </ButtonContextMenu>
       </AssetSelectControlBar>

web/src/routes/(user)/archive/[[photos=photos]]/[[assetId=id]]/+page.svelte

@@ -65,32 +65,18 @@
     assets={assetInteraction.selectedAssets}
     clearSelect={() => assetInteraction.clearMultiselect()}
   >
-    <ArchiveAction
-      unarchive
-      onArchive={(ids, visibility) =>
-        timelineManager.updateAssetOperation(ids, (asset) => {
-          asset.visibility = visibility;
-          return { remove: false };
-        })}
-    />
+    <ArchiveAction unarchive manager={timelineManager} />
     <CreateSharedLink />
     <SelectAllAssets {timelineManager} {assetInteraction} />
     <ButtonContextMenu icon={mdiPlus} title={$t('add_to')}>
       <AddToAlbum />
       <AddToAlbum shared />
     </ButtonContextMenu>
-    <FavoriteAction
-      removeFavorite={assetInteraction.isAllFavorite}
-      onFavorite={(ids, isFavorite) =>
-        timelineManager.updateAssetOperation(ids, (asset) => {
-          asset.isFavorite = isFavorite;
-          return { remove: false };
-        })}
-    />
+    <FavoriteAction removeFavorite={assetInteraction.isAllFavorite} manager={timelineManager} />
     <ButtonContextMenu icon={mdiDotsVertical} title={$t('menu')}>
       <DownloadAction menuItem />
       <SetVisibilityAction menuItem onVisibilitySet={handleSetVisibility} />
-      <DeleteAssets menuItem onAssetDelete={(assetIds) => timelineManager.removeAssets(assetIds)} />
+      <DeleteAssets menuItem manager={timelineManager} />
     </ButtonContextMenu>
   </AssetSelectControlBar>
 {/if}

web/src/routes/(user)/favorites/[[photos=photos]]/[[assetId=id]]/+page.svelte

@@ -71,7 +71,7 @@
     assets={assetInteraction.selectedAssets}
     clearSelect={() => assetInteraction.clearMultiselect()}
   >
-    <FavoriteAction removeFavorite onFavorite={(assetIds) => timelineManager.removeAssets(assetIds)} />
+    <FavoriteAction removeFavorite manager={timelineManager} />
     <CreateSharedLink />
     <SelectAllAssets {timelineManager} {assetInteraction} />
     <ButtonContextMenu icon={mdiPlus} title={$t('add_to')}>
@@ -83,20 +83,12 @@
       <ChangeDate menuItem />
       <ChangeDescription menuItem />
       <ChangeLocation menuItem />
-      <ArchiveAction
-        menuItem
-        unarchive={assetInteraction.isAllArchived}
-        onArchive={(assetIds) => timelineManager.removeAssets(assetIds)}
-      />
+      <ArchiveAction menuItem unarchive={assetInteraction.isAllArchived} manager={timelineManager} />
       {#if $preferences.tags.enabled}
         <TagAction menuItem />
       {/if}
       <SetVisibilityAction menuItem onVisibilitySet={handleSetVisibility} />
-      <DeleteAssets
-        menuItem
-        onAssetDelete={(assetIds) => timelineManager.removeAssets(assetIds)}
-        onUndoDelete={(assets) => timelineManager.addAssets(assets)}
-      />
+      <DeleteAssets menuItem manager={timelineManager} />
     </ButtonContextMenu>
   </AssetSelectControlBar>
 {/if}

web/src/routes/(user)/people/[personId]/[[photos=photos]]/[[assetId=id]]/+page.svelte

@@ -349,15 +349,8 @@
     }
   };
 
-  const handleDeleteAssets = async (assetIds: string[]) => {
-    timelineManager.removeAssets(assetIds);
-    await updateAssetCount();
-  };
-
-  const handleUndoDeleteAssets = async (assets: TimelineAsset[]) => {
-    timelineManager.addAssets(assets);
-    await updateAssetCount();
-  };
+  const handleDeleteAssets = async () => await updateAssetCount();
+  const handleUndoDeleteAssets = async () => await updateAssetCount();
 
   let person = $derived(data.person);
 
@@ -511,14 +504,7 @@
         <AddToAlbum />
         <AddToAlbum shared />
       </ButtonContextMenu>
-      <FavoriteAction
-        removeFavorite={assetInteraction.isAllFavorite}
-        onFavorite={(ids, isFavorite) =>
-          timelineManager.updateAssetOperation(ids, (asset) => {
-            asset.isFavorite = isFavorite;
-            return { remove: false };
-          })}
-      />
+      <FavoriteAction removeFavorite={assetInteraction.isAllFavorite} manager={timelineManager} />
       <ButtonContextMenu icon={mdiDotsVertical} title={$t('menu')}>
         <DownloadAction menuItem filename="{person.name || 'immich'}.zip" />
         <MenuOption
@@ -529,19 +515,16 @@
         <ChangeDate menuItem />
         <ChangeDescription menuItem />
         <ChangeLocation menuItem />
-        <ArchiveAction
-          menuItem
-          unarchive={assetInteraction.isAllArchived}
-          onArchive={(assetIds) => timelineManager.removeAssets(assetIds)}
-        />
+        <ArchiveAction menuItem unarchive={assetInteraction.isAllArchived} manager={timelineManager} />
         {#if $preferences.tags.enabled && assetInteraction.isAllUserOwned}
           <TagAction menuItem />
         {/if}
         <SetVisibilityAction menuItem onVisibilitySet={handleSetVisibility} />
         <DeleteAssets
           menuItem
-          onAssetDelete={(assetIds) => handleDeleteAssets(assetIds)}
-          onUndoDelete={(assets) => handleUndoDeleteAssets(assets)}
+          manager={timelineManager}
+          onAssetDelete={handleDeleteAssets}
+          onUndoDelete={handleUndoDeleteAssets}
         />
       </ButtonContextMenu>
     </AssetSelectControlBar>

web/src/routes/(user)/photos/[[assetId=id]]/+page.svelte

@@ -70,12 +70,12 @@
 
   const handleLink: OnLink = ({ still, motion }) => {
     timelineManager.removeAssets([motion.id]);
-    timelineManager.updateAssets([still]);
+    timelineManager.upsertAssets([still]);
   };
 
   const handleUnlink: OnUnlink = ({ still, motion }) => {
-    timelineManager.addAssets([motion]);
-    timelineManager.updateAssets([still]);
+    timelineManager.upsertAssets([motion]);
+    timelineManager.upsertAssets([still]);
   };
 
   const handleSetVisibility = (assetIds: string[]) => {
@@ -118,14 +118,7 @@
       <AddToAlbum />
       <AddToAlbum shared />
     </ButtonContextMenu>
-    <FavoriteAction
-      removeFavorite={assetInteraction.isAllFavorite}
-      onFavorite={(ids, isFavorite) =>
-        timelineManager.updateAssetOperation(ids, (asset) => {
-          asset.isFavorite = isFavorite;
-          return { remove: false };
-        })}
-    ></FavoriteAction>
+    <FavoriteAction removeFavorite={assetInteraction.isAllFavorite} manager={timelineManager}></FavoriteAction>
     <ButtonContextMenu icon={mdiDotsVertical} title={$t('menu')}>
       <DownloadAction menuItem />
       {#if assetInteraction.selectedAssets.length > 1 || isAssetStackSelected}
@@ -146,15 +139,11 @@
       <ChangeDate menuItem />
       <ChangeDescription menuItem />
       <ChangeLocation menuItem />
-      <ArchiveAction menuItem onArchive={(assetIds) => timelineManager.removeAssets(assetIds)} />
+      <ArchiveAction menuItem manager={timelineManager} />
       {#if $preferences.tags.enabled}
         <TagAction menuItem />
       {/if}
-      <DeleteAssets
-        menuItem
-        onAssetDelete={(assetIds) => timelineManager.removeAssets(assetIds)}
-        onUndoDelete={(assets) => timelineManager.addAssets(assets)}
-      />
+      <DeleteAssets menuItem manager={timelineManager} />
       <SetVisibilityAction menuItem onVisibilitySet={handleSetVisibility} />
       <hr />
       <AssetJobActions />

web/src/routes/(user)/utilities/geolocation/+page.svelte

@@ -63,7 +63,7 @@
       }),
     );
 
-    timelineManager.updateAssets(updatedAssets);
+    timelineManager.upsertAssets(updatedAssets);
 
     handleDeselectAll();
   };
@@ -195,7 +195,7 @@
     withStacked
     onThumbnailClick={handleThumbnailClick}
   >
-    {#snippet customLayout(asset: TimelineAsset)}
+    {#snippet customThumbnailLayout(asset: TimelineAsset)}
       {#if hasGps(asset)}
         <div class="absolute bottom-1 end-3 px-4 py-1 rounded-xl text-xs transition-colors bg-success text-black">
           {asset.city || $t('gps')}