From bafc36cbb2287ecb3b806cb32118a9ee9d5f7170 Mon Sep 17 00:00:00 2001
From: Adam Malczewski <github@tradam.dev>
Date: Thu, 9 Apr 2026 19:55:19 +0900
Subject: auto-caching setup

---
 src/App.svelte                            |  23 ++-
 src/lib/cache/autoCacheService.ts         | 255 ++++++++++++++++++++++++++++++
 src/lib/cache/index.ts                    |   1 +
 src/lib/components/CachedThumbnail.svelte |  38 ++++-
 src/lib/components/ImagePreview.svelte    |  13 ++
 5 files changed, 323 insertions(+), 7 deletions(-)
 create mode 100644 src/lib/cache/autoCacheService.ts

diff --git a/src/App.svelte b/src/App.svelte
index bbc0c43..7d99875 100644
--- a/src/App.svelte
+++ b/src/App.svelte
@@ -2,6 +2,7 @@
   import { flashair } from './lib/flashair';
   import type { FlashAirFileEntry } from './lib/flashair';
   import { imageCache } from './lib/cache';
+  import { autoCacheService } from './lib/cache';
   import ImageList from './lib/components/ImageList.svelte';
   import ImagePreview from './lib/components/ImagePreview.svelte';
 
@@ -20,11 +21,15 @@
   async function loadAllImages() {
     loading = true;
     error = undefined;
+    autoCacheService.stop();
     try {
       images = await flashair.listAllImages('/DCIM');
       if (images.length > 0 && selectedFile === undefined) {
         selectedFile = images[0];
       }
+      if (images.length > 0) {
+        autoCacheService.start(images);
+      }
     } catch (e) {
       error = e instanceof Error ? e.message : String(e);
       images = [];
@@ -50,9 +55,10 @@
     deleting = true;
     try {
       await flashair.deleteFile(fileToDelete.path);
-      // Remove from cache
+      // Remove from cache and auto-cache queue
       void imageCache.delete('thumbnail', fileToDelete.path);
       void imageCache.delete('full', fileToDelete.path);
+      autoCacheService.removeImage(fileToDelete.path);
       // Remove from list and select next image
       const idx = images.findIndex((f) => f.path === fileToDelete.path);
       images = images.filter((f) => f.path !== fileToDelete.path);
@@ -73,6 +79,15 @@
   function cancelDelete() {
     showDeleteConfirm = false;
   }
+
+  async function clearAllCache() {
+    autoCacheService.stop();
+    await imageCache.clear();
+    // Restart auto-caching from scratch
+    if (images.length > 0) {
+      autoCacheService.start(images);
+    }
+  }
 </script>
 
 <div class="flex h-screen bg-base-200">
@@ -144,6 +159,12 @@
       </svg>
     {/if}
   </button>
+  <!-- Clear Cache -->
+  <button class="btn btn-lg btn-circle btn-warning" onclick={() => void clearAllCache()}>
+    <svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5" stroke="currentColor" class="size-5">
+      <path stroke-linecap="round" stroke-linejoin="round" d="M20.25 7.5l-.625 10.632a2.25 2.25 0 0 1-2.247 2.118H6.622a2.25 2.25 0 0 1-2.247-2.118L3.75 7.5m6 4.125l2.25 2.25m0 0l2.25 2.25M12 13.875l2.25-2.25M12 13.875l-2.25 2.25M3.375 7.5h17.25c.621 0 1.125-.504 1.125-1.125v-1.5c0-.621-.504-1.125-1.125-1.125H3.375c-.621 0-1.125.504-1.125 1.125v1.5c0 .621.504 1.125 1.125 1.125Z" />
+    </svg>
+  </button>
   <!-- Refresh -->
   <button class="btn btn-lg btn-circle btn-secondary" onclick={() => loadAllImages()}>
     <svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5" stroke="currentColor" class="size-5">
diff --git a/src/lib/cache/autoCacheService.ts b/src/lib/cache/autoCacheService.ts
new file mode 100644
index 0000000..04dc92b
--- /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();
diff --git a/src/lib/cache/index.ts b/src/lib/cache/index.ts
index 7ce52dc..18f873b 100644
--- a/src/lib/cache/index.ts
+++ b/src/lib/cache/index.ts
@@ -1,2 +1,3 @@
 export { imageCache } from './imageCache';
 export type { CachedImage } from './imageCache';
+export { autoCacheService } from './autoCacheService';
diff --git a/src/lib/components/CachedThumbnail.svelte b/src/lib/components/CachedThumbnail.svelte
index f0fe8bf..3a6d452 100644
--- a/src/lib/components/CachedThumbnail.svelte
+++ b/src/lib/components/CachedThumbnail.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import { flashair } from '../flashair';
   import { imageCache } from '../cache';
+  import { autoCacheService } from '../cache';
 
   interface Props {
     path: string;
@@ -11,6 +12,7 @@
 
   let blobUrl = $state<string | undefined>(undefined);
   let rawBlobUrl: string | undefined;
+  let cacheProgress = $state<number | undefined>(undefined);
 
   $effect(() => {
     const currentPath = path;
@@ -26,6 +28,17 @@
     };
   });
 
+  // Subscribe to auto-cache progress updates
+  $effect(() => {
+    const currentPath = path;
+    const unsubscribe = autoCacheService.subscribe(() => {
+      cacheProgress = autoCacheService.getProgress(currentPath);
+    });
+    // Set initial value
+    cacheProgress = autoCacheService.getProgress(currentPath);
+    return unsubscribe;
+  });
+
   async function loadThumbnail(filePath: string) {
     // Try cache first
     const cached = await imageCache.get('thumbnail', filePath);
@@ -51,15 +64,28 @@
       // Thumbnail fetch failed — show placeholder
     }
   }
+
+  let cachePercent = $derived(
+    cacheProgress !== undefined ? Math.round(cacheProgress * 100) : undefined
+  );
 </script>
 
 {#if blobUrl !== undefined}
-  <img
-    src={blobUrl}
-    {alt}
-    class="w-full aspect-square rounded object-cover"
-    draggable="false"
-  />
+  <div class="relative w-full aspect-square">
+    <img
+      src={blobUrl}
+      {alt}
+      class="w-full aspect-square rounded object-cover"
+      draggable="false"
+    />
+    {#if cachePercent !== undefined && cachePercent < 100}
+      <div class="absolute inset-0 flex items-center justify-center">
+        <div class="radial-progress text-primary bg-base-300/60 border-2 border-base-300/60" style:--value={cachePercent} style:--size="2.5rem" style:--thickness="3px" role="progressbar">
+          <span class="text-[0.6rem] font-bold text-primary-content drop-shadow">{cachePercent}%</span>
+        </div>
+      </div>
+    {/if}
+  </div>
 {:else}
   <div class="w-full aspect-square rounded bg-base-300 flex items-center justify-center">
     <span class="loading loading-spinner loading-sm"></span>
diff --git a/src/lib/components/ImagePreview.svelte b/src/lib/components/ImagePreview.svelte
index f5032a6..20a9937 100644
--- a/src/lib/components/ImagePreview.svelte
+++ b/src/lib/components/ImagePreview.svelte
@@ -2,6 +2,7 @@
   import { flashair } from '../flashair';
   import type { FlashAirFileEntry } from '../flashair';
   import { imageCache } from '../cache';
+  import { autoCacheService } from '../cache';
 
   interface Props {
     file: FlashAirFileEntry | undefined;
@@ -251,6 +252,12 @@
         currentAbort.abort();
         currentAbort = undefined;
       }
+      // If we were downloading and got aborted (e.g. user navigated away),
+      // make sure to resume the auto-cache service.
+      if (downloading) {
+        downloading = false;
+        autoCacheService.resumeAfterUserDownload();
+      }
     };
   });
 
@@ -330,12 +337,14 @@
       fullObjectUrl = objectUrl;
       progress = 1;
       downloading = false;
+      autoCacheService.markCached(entry.path);
       return;
     }
 
     downloading = true;
     progress = 0;
     loadError = undefined;
+    autoCacheService.pauseForUserDownload();
 
     const url = flashair.fileUrl(entry.path);
     const totalBytes = entry.size;
@@ -352,11 +361,13 @@
         if (abort.signal.aborted) return;
         // Store in cache (fire-and-forget)
         void imageCache.put('full', entry.path, blob);
+        autoCacheService.markCached(entry.path);
         const objectUrl = URL.createObjectURL(blob);
         rawObjectUrl = objectUrl;
         fullObjectUrl = objectUrl;
         progress = 1;
         downloading = false;
+        autoCacheService.resumeAfterUserDownload();
         return;
       }
 
@@ -376,6 +387,7 @@
       const blob = new Blob(chunks);
       // Store in cache (fire-and-forget)
       void imageCache.put('full', entry.path, blob);
+      autoCacheService.markCached(entry.path);
       const objectUrl = URL.createObjectURL(blob);
       rawObjectUrl = objectUrl;
       fullObjectUrl = objectUrl;
@@ -386,6 +398,7 @@
     } finally {
       if (!abort.signal.aborted) {
         downloading = false;
+        autoCacheService.resumeAfterUserDownload();
       }
     }
   }
-- 
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