From d71a2c3d8185b2fab25a651817e8adbf8677e04f Mon Sep 17 00:00:00 2001
From: Anthony Stirling <77850077+Frooodle@users.noreply.github.com>
Date: Wed, 22 Apr 2026 14:33:38 +0100
Subject: [PATCH] FixThumbnailRegeneration (#6134)

---
 .../src/core/hooks/useIndexedDBThumbnail.ts   | 101 ++++++++++--------
 1 file changed, 54 insertions(+), 47 deletions(-)

diff --git a/frontend/src/core/hooks/useIndexedDBThumbnail.ts b/frontend/src/core/hooks/useIndexedDBThumbnail.ts
index 5ee9e45e26..3b454e6849 100644
--- a/frontend/src/core/hooks/useIndexedDBThumbnail.ts
+++ b/frontend/src/core/hooks/useIndexedDBThumbnail.ts
@@ -3,6 +3,7 @@ import { StirlingFileStub } from "@app/types/fileContext";
 import { useIndexedDB } from "@app/contexts/IndexedDBContext";
 import { generateThumbnailForFile } from "@app/utils/thumbnailUtils";
 import { FileId } from "@app/types/fileContext";
+import { useFileManagement } from "@app/contexts/FileContext";
 
 /**
  * Hook for IndexedDB-aware thumbnail loading
@@ -17,6 +18,7 @@ export function useIndexedDBThumbnail(
   const [thumb, setThumb] = useState<string | null>(null);
   const [generating, setGenerating] = useState(false);
   const indexedDB = useIndexedDB();
+  const { updateStirlingFileStub } = useFileManagement();
 
   useEffect(() => {
     let cancelled = false;
@@ -27,58 +29,59 @@ export function useIndexedDBThumbnail(
         return;
       }
 
-      // First priority: use stored thumbnail
+      // Tier 1: stored thumbnail on the stub.
       if (file.thumbnailUrl) {
         setThumb(file.thumbnailUrl);
         return;
       }
 
-      // Second priority: generate thumbnail for files under 100MB
-      if (file.size < 100 * 1024 * 1024 && !generating) {
-        setGenerating(true);
-        try {
-          let fileObject: File;
-
-          // Try to load file from IndexedDB using new context
-          if (file.id && indexedDB) {
-            const loadedFile = await indexedDB.loadFile(file.id as FileId);
-            if (!loadedFile) {
-              throw new Error("File not found in IndexedDB");
-            }
-            fileObject = loadedFile;
-          } else {
-            throw new Error(
-              "File ID not available or IndexedDB context not available",
-            );
-          }
-
-          // Use the universal thumbnail generator
-          const thumbnail = await generateThumbnailForFile(fileObject);
-          if (!cancelled) {
-            setThumb(thumbnail);
-
-            // Save thumbnail to IndexedDB for persistence
-            if (file.id && indexedDB && thumbnail) {
-              try {
-                await indexedDB.updateThumbnail(file.id as FileId, thumbnail);
-              } catch (error) {
-                console.warn("Failed to save thumbnail to IndexedDB:", error);
-              }
-            }
-          }
-        } catch (error) {
-          console.warn(
-            "Failed to generate thumbnail for file",
-            file.name,
-            error,
-          );
-          if (!cancelled) setThumb(null);
-        } finally {
-          if (!cancelled) setGenerating(false);
-        }
-      } else {
-        // Large files - no thumbnail
+      // >=100MB files are skipped entirely — no thumbnail.
+      if (file.size >= 100 * 1024 * 1024) {
         setThumb(null);
+        return;
+      }
+
+      // Tier 2: generate on demand from the File bytes in IndexedDB.
+      // Re-entry guard is handled by the effect's cleanup/cancelled pattern —
+      // `generating` is NOT in the deps, so setGenerating() does not trigger
+      // the effect to re-run and cancel itself mid-flight.
+      setGenerating(true);
+      try {
+        if (!file.id || !indexedDB) {
+          throw new Error(
+            `missing prerequisite fileId=${file.id} indexedDB=${Boolean(indexedDB)}`,
+          );
+        }
+
+        const loadedFile = await indexedDB.loadFile(file.id as FileId);
+        if (!loadedFile) {
+          throw new Error("not in IndexedDB (likely remote-only stub)");
+        }
+
+        const thumbnail = await generateThumbnailForFile(loadedFile);
+        if (cancelled) return;
+
+        setThumb(thumbnail);
+
+        if (file.id && indexedDB && thumbnail) {
+          try {
+            await indexedDB.updateThumbnail(file.id as FileId, thumbnail);
+            // Also sync the in-memory stub so subsequent re-mounts hit tier 1
+            // instead of regenerating. IndexedDB persistence alone only helps
+            // the next page load; the current session reads file.thumbnailUrl
+            // from the FileContext stub.
+            updateStirlingFileStub(file.id as FileId, {
+              thumbnailUrl: thumbnail,
+            });
+          } catch (error) {
+            console.warn("Failed to persist thumbnail:", error);
+          }
+        }
+      } catch (error) {
+        console.warn("Failed to generate thumbnail for file", file.name, error);
+        if (!cancelled) setThumb(null);
+      } finally {
+        if (!cancelled) setGenerating(false);
       }
     }
 
@@ -86,7 +89,11 @@ export function useIndexedDBThumbnail(
     return () => {
       cancelled = true;
     };
-  }, [file, file?.thumbnailUrl, file?.id, indexedDB, generating]);
+    // `generating` is intentionally NOT in the deps — it's an internal flag
+    // set by this effect, and including it caused the effect to cancel
+    // itself mid-flight (orphaning the render and leaving generating=true
+    // stuck forever).
+  }, [file, file?.thumbnailUrl, file?.id, indexedDB, updateStirlingFileStub]);
 
   return { thumbnail: thumb, isGenerating: generating };
 }