feat(web): add asset navigation and simplify photostream architecture

- Add findNextAsset, findPreviousAsset, and findRandomAsset methods
  to PhotostreamManager
  - Move layout() and findAssetAbsolutePosition() to PhotostreamSegment
   base class
  - Create SimplePhotostreamManager for basic photostream functionalityw

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

@@ -305,4 +305,63 @@ export abstract class PhotostreamManager {
     // Return the IDs that were not found/removed
     return assetIds.filter((id) => !removedIds.includes(id));
   }
+
+  findNextAsset(currentAssetId: string): { id: string } | undefined {
+    for (let segmentIndex = 0; segmentIndex < this.months.length; segmentIndex++) {
+      const segment = this.months[segmentIndex];
+      const assetIndex = segment.assets.findIndex((asset) => asset.id === currentAssetId);
+
+      if (assetIndex !== -1) {
+        // Found the current asset
+        if (assetIndex < segment.assets.length - 1) {
+          // Next asset is in the same segment
+          return segment.assets[assetIndex + 1];
+        } else if (segmentIndex < this.months.length - 1) {
+          // Next asset is in the next segment
+          const nextSegment = this.months[segmentIndex + 1];
+          if (nextSegment.assets.length > 0) {
+            return nextSegment.assets[0];
+          }
+        }
+        break;
+      }
+    }
+    return undefined;
+  }
+
+  findPreviousAsset(currentAssetId: string): { id: string } | undefined {
+    for (let segmentIndex = 0; segmentIndex < this.months.length; segmentIndex++) {
+      const segment = this.months[segmentIndex];
+      const assetIndex = segment.assets.findIndex((asset) => asset.id === currentAssetId);
+
+      if (assetIndex !== -1) {
+        // Found the current asset
+        if (assetIndex > 0) {
+          // Previous asset is in the same segment
+          return segment.assets[assetIndex - 1];
+        } else if (segmentIndex > 0) {
+          // Previous asset is in the previous segment
+          const previousSegment = this.months[segmentIndex - 1];
+          if (previousSegment.assets.length > 0) {
+            return previousSegment.assets.at(-1);
+          }
+        }
+        break;
+      }
+    }
+    return undefined;
+  }
+
+  findRandomAsset(): { id: string } | undefined {
+    // Get all loaded assets across all segments
+    const allAssets = this.months.flatMap((segment) => segment.assets);
+
+    if (allAssets.length === 0) {
+      return undefined;
+    }
+
+    // Return a random asset
+    const randomIndex = Math.floor(Math.random() * allAssets.length);
+    return allAssets[randomIndex];
+  }
 }

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

@@ -7,6 +7,7 @@ import type { PhotostreamManager } from '$lib/managers/photostream-manager/Photo
 import { getTestHook } from '$lib/managers/photostream-manager/TestHooks.svelte';
 import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
 import type { ViewerAsset } from '$lib/managers/timeline-manager/viewer-asset.svelte';
+import { getJustifiedLayoutFromAssets, getPosition } from '$lib/utils/layout-utils';
 
 export type SegmentIdentifier = {
   matches(segment: PhotostreamSegment): boolean;
@@ -144,12 +145,31 @@ export abstract class PhotostreamSegment {
     this.loader?.cancel();
   }
 
-  layout(_?: boolean) {}
+  layout(): void {
+    const timelineAssets = this.viewerAssets.map((viewerAsset) => viewerAsset.asset);
+    const layoutOptions = this.timelineManager.layoutOptions;
+    const geometry = getJustifiedLayoutFromAssets(timelineAssets, layoutOptions);
+    this.height = timelineAssets.length === 0 ? 0 : geometry.containerHeight + this.timelineManager.headerHeight;
+    for (let i = 0; i < this.viewerAssets.length; i++) {
+      const position = getPosition(geometry, i);
+      this.viewerAssets[i].position = position;
+    }
+  }
 
   updateIntersection({ intersecting, actuallyIntersecting }: { intersecting: boolean; actuallyIntersecting: boolean }) {
     this.intersecting = intersecting;
     this.actuallyIntersecting = actuallyIntersecting;
   }
 
-  abstract findAssetAbsolutePosition(assetId: string): number;
+  findAssetAbsolutePosition(assetId: string) {
+    const viewerAsset = this.viewerAssets.find((viewAsset) => viewAsset.id === assetId);
+    if (viewerAsset) {
+      if (!viewerAsset.position) {
+        console.warn('No position for asset');
+        return -1;
+      }
+      return this.top + viewerAsset.position.top + this.timelineManager.headerHeight;
+    }
+    return -1;
+  }
 }

web/src/lib/managers/searchresults-manager/SearchResultsSegment.svelte.ts

@@ -7,7 +7,6 @@ import type {
   SearchTerms,
 } from '$lib/managers/searchresults-manager/SearchResultsManager.svelte';
 import { ViewerAsset } from '$lib/managers/timeline-manager/viewer-asset.svelte';
-import { getJustifiedLayoutFromAssets, getPosition } from '$lib/utils/layout-utils';
 import { toTimelineAsset } from '$lib/utils/timeline-util';
 import { TUNABLES } from '$lib/utils/tunables';
 import { searchAssets, searchSmart } from '@immich/sdk';
@@ -72,18 +71,6 @@ export class SearchResultsSegment extends PhotostreamSegment {
     this.layout();
   }
 
-  layout(): void {
-    const timelineAssets = this.#viewerAssets.map((viewerAsset) => viewerAsset.asset);
-    const layoutOptions = this.timelineManager.layoutOptions;
-    const geometry = getJustifiedLayoutFromAssets(timelineAssets, layoutOptions);
-
-    this.height = timelineAssets.length === 0 ? 0 : geometry.containerHeight + this.timelineManager.headerHeight;
-    for (let i = 0; i < this.#viewerAssets.length; i++) {
-      const position = getPosition(geometry, i);
-      this.#viewerAssets[i].position = position;
-    }
-  }
-
   get viewerAssets(): ViewerAsset[] {
     return this.#viewerAssets;
   }

web/src/lib/managers/simple-photostream-manager/SimplePhotostreamManager.ts

@@ -0,0 +1,50 @@
+import { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
+import {
+  PhotostreamSegment,
+  type SegmentIdentifier,
+} from '$lib/managers/photostream-manager/PhotostreamSegment.svelte';
+import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
+import { ViewerAsset } from '$lib/managers/timeline-manager/viewer-asset.svelte';
+
+function createSimpleSegment(manager: SimplePhotostreamManager, assets: TimelineAsset[]) {
+  class SimpleSegment extends PhotostreamSegment {
+    #viewerAssets = $derived(assets.map((asset) => new ViewerAsset(this, asset)));
+    #identifier = {
+      matches: () => true,
+    };
+    get timelineManager(): PhotostreamManager {
+      return manager;
+    }
+    get identifier(): SegmentIdentifier {
+      return this.#identifier;
+    }
+    get id(): string {
+      return 'one';
+    }
+    protected fetch(): Promise<void> {
+      return Promise.resolve();
+    }
+    get viewerAssets(): ViewerAsset[] {
+      return this.#viewerAssets;
+    }
+  }
+  return new SimpleSegment();
+}
+
+export class SimplePhotostreamManager extends PhotostreamManager {
+  #assets: TimelineAsset[] = $state([]);
+  #segment: PhotostreamSegment;
+
+  constructor() {
+    super();
+    this.#segment = createSimpleSegment(this, this.#assets);
+  }
+
+  set assets(assets: TimelineAsset[]) {
+    this.#assets = assets;
+  }
+
+  get months(): PhotostreamSegment[] {
+    return [this.#segment];
+  }
+}