From 054f063f1f77442c7091d1ff4b7bed7bd2e2245d Mon Sep 17 00:00:00 2001
From: Jannis Braun <151788261+TheZwiss@users.noreply.github.com>
Date: Thu, 30 Apr 2026 02:03:01 +0200
Subject: [PATCH] feat(web): IDB persistence + capability detection for
 FileSystemFileHandle

---
 packages/web/src/utils/idbHandles.test.ts | 44 +++++++++++++
 packages/web/src/utils/idbHandles.ts      | 76 +++++++++++++++++++++++
 2 files changed, 120 insertions(+)
 create mode 100644 packages/web/src/utils/idbHandles.test.ts
 create mode 100644 packages/web/src/utils/idbHandles.ts

diff --git a/packages/web/src/utils/idbHandles.test.ts b/packages/web/src/utils/idbHandles.test.ts
new file mode 100644
index 00000000..84b64079
--- /dev/null
+++ b/packages/web/src/utils/idbHandles.test.ts
@@ -0,0 +1,44 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import 'fake-indexeddb/auto';
+import { putHandle, getHandle, deleteHandle, clearAllHandles, supportsFsHandles, supportsDnDHandles } from './idbHandles';
+
+describe('idbHandles', () => {
+  beforeEach(async () => { await clearAllHandles(); });
+
+  it('round-trips a structured-cloneable handle stand-in', async () => {
+    const fakeHandle = { kind: 'file', name: 'photo.png' } as unknown as FileSystemHandle;
+    await putHandle('t-1', fakeHandle);
+    const read = await getHandle('t-1');
+    expect(read).toEqual(fakeHandle);
+  });
+
+  it('returns undefined for missing key', async () => {
+    expect(await getHandle('t-missing')).toBeUndefined();
+  });
+
+  it('deletes a stored handle', async () => {
+    await putHandle('t-2', { kind: 'file' } as unknown as FileSystemHandle);
+    await deleteHandle('t-2');
+    expect(await getHandle('t-2')).toBeUndefined();
+  });
+
+  it('deleteHandle on a missing key is a no-op (no throw)', async () => {
+    await expect(deleteHandle('t-never')).resolves.toBeUndefined();
+  });
+
+  it('clearAllHandles empties the store', async () => {
+    await putHandle('t-3', { kind: 'file' } as unknown as FileSystemHandle);
+    await putHandle('t-4', { kind: 'file' } as unknown as FileSystemHandle);
+    await clearAllHandles();
+    expect(await getHandle('t-3')).toBeUndefined();
+    expect(await getHandle('t-4')).toBeUndefined();
+  });
+
+  it('supportsFsHandles returns a boolean', () => {
+    expect(typeof supportsFsHandles()).toBe('boolean');
+  });
+
+  it('supportsDnDHandles returns a boolean', () => {
+    expect(typeof supportsDnDHandles()).toBe('boolean');
+  });
+});
diff --git a/packages/web/src/utils/idbHandles.ts b/packages/web/src/utils/idbHandles.ts
new file mode 100644
index 00000000..4018c042
--- /dev/null
+++ b/packages/web/src/utils/idbHandles.ts
@@ -0,0 +1,76 @@
+import { openDB, type IDBPDatabase } from 'idb';
+
+const DB_NAME = 'backspace-transfers';
+const STORE = 'fs-handles';
+const VERSION = 1;
+
+let dbPromise: Promise<IDBPDatabase> | null = null;
+
+function getDB(): Promise<IDBPDatabase> {
+  if (!dbPromise) {
+    dbPromise = openDB(DB_NAME, VERSION, {
+      upgrade(db) {
+        if (!db.objectStoreNames.contains(STORE)) {
+          db.createObjectStore(STORE);
+        }
+      },
+    });
+  }
+  return dbPromise;
+}
+
+/** Store a FileSystemFileHandle (or any structured-cloneable handle) under a key. */
+export async function putHandle(key: string, handle: FileSystemHandle): Promise<void> {
+  const db = await getDB();
+  await db.put(STORE, handle, key);
+}
+
+/** Retrieve a stored handle, or undefined if not present. */
+export async function getHandle(key: string): Promise<FileSystemHandle | undefined> {
+  const db = await getDB();
+  return db.get(STORE, key);
+}
+
+/** Delete a stored handle. No-op if missing. */
+export async function deleteHandle(key: string): Promise<void> {
+  const db = await getDB();
+  await db.delete(STORE, key);
+}
+
+/** Wipe every handle from the store. Used in tests and on logout. */
+export async function clearAllHandles(): Promise<void> {
+  const db = await getDB();
+  await db.clear(STORE);
+}
+
+/** True iff the browser exposes the FS Access file picker (Chrome/Edge). */
+export function supportsFsHandles(): boolean {
+  return typeof (window as unknown as { showOpenFilePicker?: unknown }).showOpenFilePicker === 'function';
+}
+
+/** True iff DataTransferItem.getAsFileSystemHandle is available (Chrome/Edge drag-drop). */
+export function supportsDnDHandles(): boolean {
+  return typeof DataTransferItem !== 'undefined'
+    && typeof (DataTransferItem.prototype as unknown as { getAsFileSystemHandle?: unknown }).getAsFileSystemHandle === 'function';
+}
+
+/**
+ * Re-prompt for permission on a stored handle. Returns 'granted', 'denied', or 'prompt'.
+ * Some non-standard FS Access surfaces don't expose `queryPermission`/`requestPermission` —
+ * if missing, returns 'denied' so callers fall back to re-pick.
+ */
+export async function ensurePermission(
+  handle: FileSystemHandle,
+  mode: 'read' | 'readwrite',
+): Promise<PermissionState> {
+  const opts = { mode };
+  const handleAny = handle as unknown as {
+    queryPermission?: (opts: { mode: string }) => Promise<PermissionState>;
+    requestPermission?: (opts: { mode: string }) => Promise<PermissionState>;
+  };
+  if (typeof handleAny.queryPermission !== 'function') return 'denied';
+  const current = await handleAny.queryPermission(opts);
+  if (current === 'granted') return 'granted';
+  if (typeof handleAny.requestPermission !== 'function') return 'denied';
+  return handleAny.requestPermission(opts);
+}