refactor(web): extract common timeline functionality into PhotostreamManager base classes

Create abstract PhotostreamManager and PhotostreamSegment base classes to enable reusable      
timeline-like components. This refactoring extracts common viewport management, scroll         
handling, and segment operations from TimelineManager and MonthGroup into reusable             
abstractions.                                                                                  
                                                                                                  
Changes:                                                                                       
 - Add PhotostreamManager.svelte.ts with viewport and scroll management                         
 - Add PhotostreamSegment.svelte.ts with segment positioning and intersection logic             
 - Refactor TimelineManager to extend PhotostreamManager                                        
 - Refactor MonthGroup to extend PhotostreamSegment                                             
 - Add utility functions for segment identification and date formatting                         
 - Update tests to reflect new inheritance structure

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();
+    }
+  }
 }