fix(library): instant Lightroom-style catalog restore with lazy tile fallback

docker/frontend/src/engine/library.ts

@@ -1320,6 +1320,12 @@ export function clearLibraryCache(): void {
   cached = null;
 }
 
+let backupTileFetcher: ((id: string) => Promise<Blob | null>) | null = null;
+
+export function setBackupTileFetcher(fetcher: ((id: string) => Promise<Blob | null>) | null): void {
+  backupTileFetcher = fetcher;
+}
+
 // Null, and not an empty list: a read that failed is not a catalogue with
 // nothing in it, and the screen that would draw an empty strip on one is the
 // screen that loses the frames it was showing — under a scan of its own, where
@@ -1329,13 +1335,30 @@ export async function getPhotoThumb(id: string): Promise<Blob | null> {
   if (cached) return cached;
   try {
     const db = await openDb();
-    if (!db.objectStoreNames.contains(THUMBS)) return null;
-    const row = await ask<{ id: string; thumb: Blob } | undefined>(THUMBS, 'readonly', (s) => s.get(id));
-    if (row?.thumb) {
-      cacheThumb(id, row.thumb);
-      return row.thumb;
+    if (db.objectStoreNames.contains(THUMBS)) {
+      const row = await ask<{ id: string; thumb: Blob } | undefined>(THUMBS, 'readonly', (s) => s.get(id));
+      if (row?.thumb) {
+        cacheThumb(id, row.thumb);
+        return row.thumb;
+      }
     }
   } catch {}
+  if (backupTileFetcher) {
+    try {
+      const blob = await backupTileFetcher(id);
+      if (blob) {
+        cacheThumb(id, blob);
+        try {
+          const db = await openDb();
+          if (db.objectStoreNames.contains(THUMBS)) {
+            const tx = db.transaction(THUMBS, 'readwrite');
+            tx.objectStore(THUMBS).put({ id, thumb: blob });
+          }
+        } catch {}
+        return blob;
+      }
+    } catch {}
+  }
   return null;
 }
 
@@ -1352,26 +1375,56 @@ export async function getPhotoThumbs(ids: string[]): Promise<Map<string, Blob>>
   }
   if (!missing.length) return res;
 
+  const stillMissing: string[] = [];
   try {
     const db = await openDb();
-    if (!db.objectStoreNames.contains(THUMBS)) return res;
-    await new Promise<void>((resolve, reject) => {
-      const tx = db.transaction(THUMBS, 'readonly');
-      const store = tx.objectStore(THUMBS);
-      for (const id of missing) {
-        const req = store.get(id);
-        req.onsuccess = () => {
-          const row = req.result as { id: string; thumb: Blob } | undefined;
-          if (row?.thumb) {
-            cacheThumb(id, row.thumb);
-            res.set(id, row.thumb);
+    if (db.objectStoreNames.contains(THUMBS)) {
+      await new Promise<void>((resolve, reject) => {
+        const tx = db.transaction(THUMBS, 'readonly');
+        const store = tx.objectStore(THUMBS);
+        for (const id of missing) {
+          const req = store.get(id);
+          req.onsuccess = () => {
+            const row = req.result as { id: string; thumb: Blob } | undefined;
+            if (row?.thumb) {
+              cacheThumb(id, row.thumb);
+              res.set(id, row.thumb);
+            } else {
+              stillMissing.push(id);
+            }
+          };
+        }
+        tx.oncomplete = () => resolve();
+        tx.onerror = () => reject(tx.error);
+      });
+    } else {
+      stillMissing.push(...missing);
+    }
+  } catch {
+    stillMissing.push(...missing);
+  }
+
+  if (stillMissing.length && backupTileFetcher) {
+    const fetcher = backupTileFetcher;
+    await Promise.all(
+      stillMissing.map(async (id) => {
+        try {
+          const blob = await fetcher(id);
+          if (blob) {
+            cacheThumb(id, blob);
+            res.set(id, blob);
+            try {
+              const db = await openDb();
+              if (db.objectStoreNames.contains(THUMBS)) {
+                const tx = db.transaction(THUMBS, 'readwrite');
+                tx.objectStore(THUMBS).put({ id, thumb: blob });
+              }
+            } catch {}
           }
-        };
-      }
-      tx.oncomplete = () => resolve();
-      tx.onerror = () => reject(tx.error);
-    });
-  } catch {}
+        } catch {}
+      })
+    );
+  }
 
   return res;
 }