Add tests and enhance local draft storage handling

src/serialization/local-draft-storage.ts

@@ -8,38 +8,139 @@ export interface KeyValueStorage {
   removeItem(key: string): void;
 }
 
+export interface BrowserStorageAccessResult {
+  storage: KeyValueStorage | null;
+  diagnostic: string | null;
+}
+
+export type SaveSceneDocumentDraftResult =
+  | { status: "saved"; message: string }
+  | { status: "error"; message: string };
+
+export type LoadSceneDocumentDraftResult =
+  | { status: "loaded"; document: SceneDocument; message: string }
+  | { status: "missing"; message: string }
+  | { status: "error"; message: string };
+
+export interface LoadOrCreateSceneDocumentResult {
+  document: SceneDocument;
+  diagnostic: string | null;
+}
+
 export const DEFAULT_SCENE_DRAFT_STORAGE_KEY = "webeditor3d.scene-document-draft";
 
-export function getBrowserStorage(): KeyValueStorage | null {
-  if (typeof window === "undefined") {
-    return null;
+function getErrorDetail(error: unknown): string {
+  if (error instanceof Error && error.message.trim().length > 0) {
+    return error.message.trim();
   }
 
-  return window.localStorage;
+  return "Unknown error.";
+}
+
+function formatStorageDiagnostic(prefix: string, error: unknown): string {
+  return `${prefix} ${getErrorDetail(error)}`;
+}
+
+export function getBrowserStorageAccess(): BrowserStorageAccessResult {
+  if (typeof window === "undefined") {
+    return {
+      storage: null,
+      diagnostic: null
+    };
+  }
+
+  try {
+    return {
+      storage: window.localStorage,
+      diagnostic: null
+    };
+  } catch (error) {
+    return {
+      storage: null,
+      diagnostic: formatStorageDiagnostic("Browser local storage is unavailable.", error)
+    };
+  }
+}
+
+export function getBrowserStorage(): KeyValueStorage | null {
+  return getBrowserStorageAccess().storage;
 }
 
 export function saveSceneDocumentDraft(
   storage: KeyValueStorage,
   document: SceneDocument,
   key = DEFAULT_SCENE_DRAFT_STORAGE_KEY
-) {
-  storage.setItem(key, serializeSceneDocument(document));
-}
+): SaveSceneDocumentDraftResult {
+  try {
+    storage.setItem(key, serializeSceneDocument(document));
 
-export function loadSceneDocumentDraft(storage: KeyValueStorage, key = DEFAULT_SCENE_DRAFT_STORAGE_KEY): SceneDocument | null {
-  const rawDocument = storage.getItem(key);
-
-  if (rawDocument === null) {
-    return null;
+    return {
+      status: "saved",
+      message: "Local draft saved."
+    };
+  } catch (error) {
+    return {
+      status: "error",
+      message: formatStorageDiagnostic("Local draft could not be saved.", error)
+    };
   }
-
-  return parseSceneDocumentJson(rawDocument);
 }
 
-export function loadOrCreateSceneDocument(storage: KeyValueStorage | null, key = DEFAULT_SCENE_DRAFT_STORAGE_KEY): SceneDocument {
+export function loadSceneDocumentDraft(
+  storage: KeyValueStorage,
+  key = DEFAULT_SCENE_DRAFT_STORAGE_KEY
+): LoadSceneDocumentDraftResult {
+  try {
+    const rawDocument = storage.getItem(key);
+
+    if (rawDocument === null) {
+      return {
+        status: "missing",
+        message: "No local draft was found."
+      };
+    }
+
+    return {
+      status: "loaded",
+      document: parseSceneDocumentJson(rawDocument),
+      message: "Local draft loaded."
+    };
+  } catch (error) {
+    return {
+      status: "error",
+      message: formatStorageDiagnostic("Stored local draft could not be loaded.", error)
+    };
+  }
+}
+
+export function loadOrCreateSceneDocument(
+  storage: KeyValueStorage | null,
+  key = DEFAULT_SCENE_DRAFT_STORAGE_KEY
+): LoadOrCreateSceneDocumentResult {
   if (storage === null) {
-    return createEmptySceneDocument();
+    return {
+      document: createEmptySceneDocument(),
+      diagnostic: null
+    };
   }
 
-  return loadSceneDocumentDraft(storage, key) ?? createEmptySceneDocument();
+  const draftResult = loadSceneDocumentDraft(storage, key);
+
+  switch (draftResult.status) {
+    case "loaded":
+      return {
+        document: draftResult.document,
+        diagnostic: null
+      };
+    case "missing":
+      return {
+        document: createEmptySceneDocument(),
+        diagnostic: null
+      };
+    case "error":
+      return {
+        document: createEmptySceneDocument(),
+        diagnostic: `${draftResult.message} Starting with a fresh empty document.`
+      };
+  }
 }