feat(chat): save messages in session storage

packages/instantsearch.js/src/lib/chat/__tests__/chat.test.ts

@@ -0,0 +1,98 @@
+import { ChatState, CACHE_KEY } from '../chat';
+
+// mock AbstractChat to avoid "TypeError: Class extends value undefined is not a constructor or null"
+jest.mock('ai', () => {
+  return {
+    AbstractChat: class {},
+  };
+});
+
+describe('ChatState', () => {
+  beforeAll(() => {
+    // Mock sessionStorage for the tests
+    const sessionStorageMock = (() => {
+      const store: Record<string, string> = {};
+      return {
+        getItem(key: string) {
+          return store[key] || null;
+        },
+        setItem(key: string, value: string) {
+          store[key] = value.toString();
+        },
+        removeItem(key: string) {
+          delete store[key];
+        },
+      };
+    })();
+
+    Object.defineProperty(globalThis, 'sessionStorage', {
+      value: sessionStorageMock,
+    });
+  });
+
+  beforeEach(() => {
+    // Clear sessionStorage before each test
+    sessionStorage.removeItem(CACHE_KEY);
+  });
+
+  afterAll(() => {
+    // Clean up the mock
+    delete (globalThis as any).sessionStorage;
+  });
+
+  it('should save messages to sessionStorage when status changes to ready', () => {
+    const chatState = new ChatState<any>();
+    const message = { role: 'user', content: 'Hello' };
+    chatState.status = 'submitted';
+    chatState.messages = [message];
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(null);
+
+    chatState.status = 'streaming';
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(null);
+
+    chatState.status = 'ready';
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(JSON.stringify([message]));
+  });
+
+  it('should load initial messages from sessionStorage', () => {
+    const initialMessages = [
+      { role: 'user', content: 'Hello' },
+      { role: 'bot', content: 'Hi there!' },
+    ];
+    sessionStorage.setItem(CACHE_KEY, JSON.stringify(initialMessages));
+
+    const chatState = new ChatState();
+    expect(chatState.messages).toEqual(initialMessages);
+  });
+
+  it('should not save messages to sessionStorage when status is not ready', () => {
+    const chatState = new ChatState<any>();
+    const message = { role: 'user', content: 'Hello' };
+    chatState.status = 'submitted';
+    chatState.messages = [message];
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(null);
+
+    chatState.status = 'streaming';
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(null);
+    chatState.status = 'error';
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(null);
+  });
+
+  it('should handle sessionStorage being unavailable', () => {
+    // eslint-disable-next-line jest/unbound-method
+    const originalSetItem = sessionStorage.setItem;
+    sessionStorage.setItem = () => {
+      throw new Error('sessionStorage is full');
+    };
+
+    const chatState = new ChatState<any>();
+    const message = { role: 'user', content: 'Hello' };
+    chatState.status = 'submitted';
+    chatState.messages = [message];
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(null);
+    chatState.status = 'ready';
+    expect(sessionStorage.getItem(CACHE_KEY)).toBe(null);
+
+    sessionStorage.setItem = originalSetItem;
+  });
+});

packages/instantsearch.js/src/lib/chat/chat.ts

@@ -11,6 +11,15 @@ export type { UIMessage };
 export { AbstractChat };
 export { ChatInit };
 
+export const CACHE_KEY = 'instantsearch-chat-initial-messages';
+
+function getDefaultInitialMessages<
+  TUIMessage extends UIMessage
+>(): TUIMessage[] {
+  const initialMessages = sessionStorage.getItem(CACHE_KEY);
+  return initialMessages ? JSON.parse(initialMessages) : [];
+}
+
 export class ChatState<TUiMessage extends UIMessage>
   implements BaseChatState<TUiMessage>
 {
@@ -22,8 +31,21 @@ export class ChatState<TUiMessage extends UIMessage>
   _statusCallbacks = new Set<() => void>();
   _errorCallbacks = new Set<() => void>();
 
-  constructor(initialMessages: TUiMessage[] = []) {
+  constructor(
+    initialMessages: TUiMessage[] = getDefaultInitialMessages<TUiMessage>()
+  ) {
     this._messages = initialMessages;
+    const saveMessagesInLocalStorage = () => {
+      if (this.status === 'ready') {
+        try {
+          sessionStorage.setItem(CACHE_KEY, JSON.stringify(this.messages));
+        } catch (e) {
+          // Do nothing if sessionStorage is not available or full
+        }
+      }
+    };
+    this['~registerMessagesCallback'](saveMessagesInLocalStorage);
+    this['~registerStatusCallback'](saveMessagesInLocalStorage);
   }
 
   get status(): ChatStatus {