FEATURE: Migrate username storage from localStorage to IndexedDB

- Created storage.js wrapper with IndexedDB support
- Automatic fallback to localStorage if IndexedDB unavailable
- Updated all username storage calls to use async API
- Better performance and more storage capacity
- Improved PWA compatibility

Benefits:
- 50MB+ storage vs 5-10MB localStorage
- Async API doesn't block main thread
- Better for future features (game history, stats, etc.)

index.html

@@ -182,6 +182,7 @@
       </div>
     </div>
 
+    <script src="storage.js"></script>
     <script src="multiplayer.js"></script>
     <script src="game.js"></script>
     <script>

multiplayer.js

@@ -21,7 +21,7 @@ class MultiplayerClient {
         }
 
         // Show username modal immediately if not saved
-        const savedUsername = localStorage.getItem('connect5_username');
+        const savedUsername = await window.gameStorage.getItem('connect5_username');
         if (!savedUsername) {
             this.showUsernameModal();
         } else {
@@ -92,13 +92,13 @@ class MultiplayerClient {
                 }
             }, 5000);
 
-            tempSocket.on('connect', () => {
+            tempSocket.on('connect', async () => {
                 clearTimeout(timeout);
                 this.socket = tempSocket;
                 console.log('✅ Socket connected, listeners ready');
                 
                 // Now that listeners are set up, handle auto-registration
-                const savedUsername = localStorage.getItem('connect5_username') || this.username;
+                const savedUsername = await window.gameStorage.getItem('connect5_username') || this.username;
                 if (savedUsername) {
                     console.log('Auto-registering with saved username:', savedUsername);
                     this.registerPlayer(savedUsername);
@@ -191,9 +191,9 @@ class MultiplayerClient {
     }
     
     // Register player
-    registerPlayer(username) {
+    async registerPlayer(username) {
         this.username = username;
-        localStorage.setItem('connect5_username', username);
+        await window.gameStorage.setItem('connect5_username', username);
         
         // Hide username modal immediately for better UX
         const modal = document.getElementById('usernameModal');
@@ -220,14 +220,12 @@ class MultiplayerClient {
     }
     
     // Handle registration response
-    handleRegistration(data) {
+    async handleRegistration(data) {
         if (data.success) {
             this.playerId = data.player.id;
             this.username = data.player.username;
-            
-            // Save username to localStorage for auto-login
-            localStorage.setItem('connect5_username', this.username);
-            console.log('Username saved to localStorage');
+            await window.gameStorage.setItem('connect5_username', this.username);
+            console.log('Username saved to IndexedDB');
             
             // Hide username modal (if visible)
             const modal = document.getElementById('usernameModal');

storage.js

@@ -0,0 +1,140 @@
+// IndexedDB wrapper for Connect-5 game data storage
+class GameStorage {
+    constructor() {
+        this.dbName = 'Connect5DB';
+        this.dbVersion = 1;
+        this.storeName = 'gameData';
+        this.db = null;
+        this.isIndexedDBSupported = this.checkIndexedDBSupport();
+    }
+
+    checkIndexedDBSupport() {
+        return 'indexedDB' in window;
+    }
+
+    async init() {
+        if (!this.isIndexedDBSupported) {
+            console.warn('IndexedDB not supported, falling back to localStorage');
+            return;
+        }
+
+        return new Promise((resolve, reject) => {
+            const request = indexedDB.open(this.dbName, this.dbVersion);
+
+            request.onerror = () => {
+                console.error('IndexedDB failed to open:', request.error);
+                reject(request.error);
+            };
+
+            request.onsuccess = () => {
+                this.db = request.result;
+                console.log('✅ IndexedDB initialized successfully');
+                resolve(this.db);
+            };
+
+            request.onupgradeneeded = (event) => {
+                const db = event.target.result;
+                
+                // Create object store if it doesn't exist
+                if (!db.objectStoreNames.contains(this.storeName)) {
+                    db.createObjectStore(this.storeName, { keyPath: 'key' });
+                    console.log('📦 Created IndexedDB object store');
+                }
+            };
+        });
+    }
+
+    async setItem(key, value) {
+        // Fallback to localStorage if IndexedDB not supported
+        if (!this.isIndexedDBSupported || !this.db) {
+            localStorage.setItem(key, value);
+            return;
+        }
+
+        return new Promise((resolve, reject) => {
+            const transaction = this.db.transaction([this.storeName], 'readwrite');
+            const store = transaction.objectStore(this.storeName);
+            const request = store.put({ key, value });
+
+            request.onsuccess = () => resolve();
+            request.onerror = () => {
+                console.error('IndexedDB setItem failed, falling back to localStorage');
+                localStorage.setItem(key, value);
+                reject(request.error);
+            };
+        });
+    }
+
+    async getItem(key) {
+        // Fallback to localStorage if IndexedDB not supported
+        if (!this.isIndexedDBSupported || !this.db) {
+            return localStorage.getItem(key);
+        }
+
+        return new Promise((resolve, reject) => {
+            const transaction = this.db.transaction([this.storeName], 'readonly');
+            const store = transaction.objectStore(this.storeName);
+            const request = store.get(key);
+
+            request.onsuccess = () => {
+                const result = request.result;
+                resolve(result ? result.value : null);
+            };
+
+            request.onerror = () => {
+                console.error('IndexedDB getItem failed, falling back to localStorage');
+                resolve(localStorage.getItem(key));
+            };
+        });
+    }
+
+    async removeItem(key) {
+        // Fallback to localStorage if IndexedDB not supported
+        if (!this.isIndexedDBSupported || !this.db) {
+            localStorage.removeItem(key);
+            return;
+        }
+
+        return new Promise((resolve, reject) => {
+            const transaction = this.db.transaction([this.storeName], 'readwrite');
+            const store = transaction.objectStore(this.storeName);
+            const request = store.delete(key);
+
+            request.onsuccess = () => resolve();
+            request.onerror = () => {
+                console.error('IndexedDB removeItem failed, falling back to localStorage');
+                localStorage.removeItem(key);
+                reject(request.error);
+            };
+        });
+    }
+
+    async clear() {
+        // Fallback to localStorage if IndexedDB not supported
+        if (!this.isIndexedDBSupported || !this.db) {
+            localStorage.clear();
+            return;
+        }
+
+        return new Promise((resolve, reject) => {
+            const transaction = this.db.transaction([this.storeName], 'readwrite');
+            const store = transaction.objectStore(this.storeName);
+            const request = store.clear();
+
+            request.onsuccess = () => resolve();
+            request.onerror = () => {
+                console.error('IndexedDB clear failed, falling back to localStorage');
+                localStorage.clear();
+                reject(request.error);
+            };
+        });
+    }
+}
+
+// Create global instance
+window.gameStorage = new GameStorage();
+
+// Initialize on page load
+window.gameStorage.init().catch(err => {
+    console.warn('Failed to initialize IndexedDB, using localStorage fallback:', err);
+});