wip: optimizations

toju-app/src/app/infrastructure/persistence/browser-database.service.ts

@@ -10,6 +10,7 @@ import {
 } from '../../shared-kernel';
 import type { ChatAttachmentMeta } from '../../shared-kernel';
 import { getStoredCurrentUserId } from '../../core/storage/current-user-storage';
+import type { RoomMessageStats } from './database.service';
 
 /** IndexedDB database name for the MetoYou application. */
 const DATABASE_NAME = 'metoyou';
@@ -110,6 +111,14 @@ export class BrowserDatabaseService {
     return this.hydrateMessages(messages);
   }
 
+  async getRoomMessageStats(roomId: string): Promise<RoomMessageStats> {
+    return this.foldMessagesForRoom(roomId, (stats, message) => {
+      stats.count += 1;
+      stats.lastUpdated = Math.max(stats.lastUpdated, message.editedAt || message.timestamp || 0);
+    }, { count: 0,
+      lastUpdated: 0 });
+  }
+
   /** Delete a message by its ID. */
   async deleteMessage(messageId: string): Promise<void> {
     await this.deleteRecord(STORE_MESSAGES, messageId);
@@ -533,6 +542,36 @@ export class BrowserDatabaseService {
     });
   }
 
+  private async foldMessagesForRoom<T>(
+    roomId: string,
+    visit: (state: T, message: Message) => void,
+    initialState: T
+  ): Promise<T> {
+    const transaction = this.createTransaction(STORE_MESSAGES, 'readonly');
+    const request = transaction.objectStore(STORE_MESSAGES)
+      .index('roomId')
+      .openCursor(IDBKeyRange.only(roomId));
+
+    return new Promise<T>((resolve, reject) => {
+      const state = initialState;
+
+      request.onsuccess = () => {
+        const cursor = request.result;
+
+        if (!cursor) {
+          resolve(state);
+          return;
+        }
+
+        visit(state, cursor.value as Message);
+        cursor.continue();
+      };
+
+      request.onerror = () => reject(request.error);
+      transaction.onabort = () => reject(transaction.error);
+    });
+  }
+
   private async deleteRecord(storeName: string, key: IDBValidKey): Promise<void> {
     const transaction = this.createTransaction(storeName, 'readwrite');