1 files changed, 255 insertions, 0 deletions
diff --git a/src/lib/cache/autoCacheService.ts b/src/lib/cache/autoCacheService.ts
new file mode 100644
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--- /dev/null
+++ b/src/lib/cache/autoCacheService.ts
@@ -0,0 +1,255 @@
+import { flashair } from '../flashair';
+import type { FlashAirFileEntry } from '../flashair';
+import { imageCache } from './imageCache';
+
+/**
+ * Reactive state for the auto-cache background service.
+ *
+ * Uses Svelte 5 $state runes via the .svelte.ts convention — but since this
+ * is a plain .ts file consumed by Svelte components, we store reactive values
+ * in a simple mutable object that components can poll or subscribe to via
+ * a wrapper.  We use a manual callback approach instead.
+ */
+
+/** Progress of a single image being auto-cached (0–1). */
+export interface AutoCacheProgress {
+  readonly path: string;
+  readonly progress: number;
+}
+
+type Listener = () => void;
+
+/**
+ * Singleton auto-cache service.
+ *
+ * Call `start(images)` after loading the image list.  The service will
+ * iterate newest-first, skip already-cached images, and download full-size
+ * images in the background one at a time.
+ *
+ * When a user-initiated download is active, call `pauseForUserDownload()`
+ * / `resumeAfterUserDownload()` to yield bandwidth.
+ */
+class AutoCacheService {
+  /** Map from image path → download progress 0–1. Only contains entries being cached. */
+  private _progressMap = new Map<string, number>();
+
+  /** Set of paths that are confirmed cached (full). */
+  private _cachedPaths = new Set<string>();
+
+  /** Whether the user is actively downloading an image. */
+  private _userDownloading = false;
+
+  /** The AbortController for the current background download. */
+  private _currentAbort: AbortController | undefined;
+
+  /** The image list to work through (newest first). */
+  private _images: FlashAirFileEntry[] = [];
+
+  /** Index of the next image to check/download. */
+  private _nextIndex = 0;
+
+  /** Whether the service is running. */
+  private _running = false;
+
+  /** Whether we're actively downloading right now. */
+  private _downloading = false;
+
+  /** Listeners notified on every progress change. */
+  private _listeners = new Set<Listener>();
+
+  /** Subscribe to state changes. Returns an unsubscribe function. */
+  subscribe(fn: Listener): () => void {
+    this._listeners.add(fn);
+    return () => {
+      this._listeners.delete(fn);
+    };
+  }
+
+  private _notify(): void {
+    for (const fn of this._listeners) {
+      fn();
+    }
+  }
+
+  /** Get progress for a specific image path. Returns undefined if not being cached. */
+  getProgress(path: string): number | undefined {
+    return this._progressMap.get(path);
+  }
+
+  /** Check if a path has been confirmed fully cached. */
+  isCached(path: string): boolean {
+    return this._cachedPaths.has(path);
+  }
+
+  /**
+   * Start (or restart) auto-caching for the given image list.
+   * Images should already be sorted newest-first.
+   */
+  start(images: readonly FlashAirFileEntry[]): void {
+    this.stop();
+    this._images = [...images];
+    this._nextIndex = 0;
+    this._running = true;
+    this._cachedPaths.clear();
+    this._progressMap.clear();
+    this._notify();
+    void this._processNext();
+  }
+
+  /** Stop all background caching. */
+  stop(): void {
+    this._running = false;
+    if (this._currentAbort !== undefined) {
+      this._currentAbort.abort();
+      this._currentAbort = undefined;
+    }
+    this._progressMap.clear();
+    this._downloading = false;
+    this._notify();
+  }
+
+  /** Mark a path as cached externally (e.g. the user just viewed it). */
+  markCached(path: string): void {
+    this._cachedPaths.add(path);
+  }
+
+  /** Pause background downloads while the user is downloading. */
+  pauseForUserDownload(): void {
+    this._userDownloading = true;
+    if (this._currentAbort !== undefined) {
+      this._currentAbort.abort();
+      this._currentAbort = undefined;
+    }
+    // Clear progress for the aborted download — it will be retried.
+    this._progressMap.clear();
+    this._downloading = false;
+    this._notify();
+  }
+
+  /** Resume background downloads after user download completes. */
+  resumeAfterUserDownload(): void {
+    this._userDownloading = false;
+    if (this._running) {
+      void this._processNext();
+    }
+  }
+
+  /** Remove a path from the work queue (e.g. after deletion). */
+  removeImage(path: string): void {
+    this._images = this._images.filter((img) => img.path !== path);
+    this._cachedPaths.delete(path);
+    this._progressMap.delete(path);
+    // Reset index to avoid skipping
+    if (this._nextIndex > this._images.length) {
+      this._nextIndex = this._images.length;
+    }
+    this._notify();
+  }
+
+  private async _processNext(): Promise<void> {
+    if (!this._running || this._userDownloading || this._downloading) return;
+
+    while (this._nextIndex < this._images.length) {
+      if (!this._running || this._userDownloading) return;
+
+      const image = this._images[this._nextIndex];
+      if (image === undefined) {
+        this._nextIndex++;
+        continue;
+      }
+
+      // Skip if already confirmed cached
+      if (this._cachedPaths.has(image.path)) {
+        this._nextIndex++;
+        continue;
+      }
+
+      // Check IndexedDB cache
+      const cached = await imageCache.get('full', image.path);
+      if (cached !== undefined) {
+        this._cachedPaths.add(image.path);
+        this._nextIndex++;
+        this._notify();
+        continue;
+      }
+
+      // Not cached — download it
+      if (this._userDownloading || !this._running) return;
+
+      const success = await this._downloadImage(image);
+      if (success) {
+        this._cachedPaths.add(image.path);
+        this._progressMap.delete(image.path);
+        this._nextIndex++;
+        this._notify();
+      } else if (this._running && !this._userDownloading) {
+        // Download failed (not aborted) — skip this image and move on
+        this._progressMap.delete(image.path);
+        this._nextIndex++;
+        this._notify();
+      }
+      // If aborted due to user download, don't advance — will retry
+    }
+  }
+
+  private async _downloadImage(image: FlashAirFileEntry): Promise<boolean> {
+    this._downloading = true;
+    const abort = new AbortController();
+    this._currentAbort = abort;
+
+    this._progressMap.set(image.path, 0);
+    this._notify();
+
+    const url = flashair.fileUrl(image.path);
+    const totalBytes = image.size;
+
+    try {
+      const res = await fetch(url, { signal: abort.signal });
+      if (!res.ok) {
+        throw new Error(`${res.status} ${res.statusText}`);
+      }
+
+      const reader = res.body?.getReader();
+      if (reader === undefined) {
+        const blob = await res.blob();
+        if (abort.signal.aborted) return false;
+        void imageCache.put('full', image.path, blob);
+        this._progressMap.set(image.path, 1);
+        this._notify();
+        return true;
+      }
+
+      const chunks: Uint8Array[] = [];
+      let received = 0;
+
+      while (true) {
+        const { done, value } = await reader.read();
+        if (done) break;
+        chunks.push(value);
+        received += value.byteLength;
+        const progress = totalBytes > 0 ? received / totalBytes : 0;
+        this._progressMap.set(image.path, progress);
+        this._notify();
+      }
+
+      if (abort.signal.aborted) return false;
+
+      const blob = new Blob(chunks);
+      void imageCache.put('full', image.path, blob);
+      this._progressMap.set(image.path, 1);
+      this._notify();
+      return true;
+    } catch (e) {
+      if (abort.signal.aborted) return false;
+      // Network error — skip this image
+      console.warn(`Auto-cache failed for ${image.path}:`, e);
+      return false;
+    } finally {
+      this._downloading = false;
+      this._currentAbort = undefined;
+    }
+  }
+}
+
+/** Singleton instance. */
+export const autoCacheService = new AutoCacheService();