Migrate canvas state storage to IndexedDB

Replaced localStorage usage in Canvas.js with asynchronous IndexedDB operations for saving, loading, and removing canvas state. Added a new db.js module to handle IndexedDB interactions, improving scalability and reliability of state persistence.

js/db.js

@@ -0,0 +1,97 @@
+const DB_NAME = 'CanvasNodeDB';
+const STORE_NAME = 'CanvasState';
+const DB_VERSION = 1;
+
+let db;
+
+function openDB() {
+    return new Promise((resolve, reject) => {
+        if (db) {
+            resolve(db);
+            return;
+        }
+
+        console.log("Opening IndexedDB...");
+        const request = indexedDB.open(DB_NAME, DB_VERSION);
+
+        request.onerror = (event) => {
+            console.error("IndexedDB error:", event.target.error);
+            reject("Error opening IndexedDB.");
+        };
+
+        request.onsuccess = (event) => {
+            db = event.target.result;
+            console.log("IndexedDB opened successfully.");
+            resolve(db);
+        };
+
+        request.onupgradeneeded = (event) => {
+            console.log("Upgrading IndexedDB...");
+            const db = event.target.result;
+            if (!db.objectStoreNames.contains(STORE_NAME)) {
+                db.createObjectStore(STORE_NAME, { keyPath: 'id' });
+                console.log("Object store created:", STORE_NAME);
+            }
+        };
+    });
+}
+
+export async function getCanvasState(id) {
+    console.log(`DB: Getting state for id: ${id}`);
+    const db = await openDB();
+    return new Promise((resolve, reject) => {
+        const transaction = db.transaction([STORE_NAME], 'readonly');
+        const store = transaction.objectStore(STORE_NAME);
+        const request = store.get(id);
+
+        request.onerror = (event) => {
+            console.error("DB: Error getting canvas state:", event.target.error);
+            reject("Error getting state.");
+        };
+
+        request.onsuccess = (event) => {
+            console.log(`DB: Get success for id: ${id}`, event.target.result ? 'found' : 'not found');
+            resolve(event.target.result ? event.target.result.state : null);
+        };
+    });
+}
+
+export async function setCanvasState(id, state) {
+    console.log(`DB: Setting state for id: ${id}`);
+    const db = await openDB();
+    return new Promise((resolve, reject) => {
+        const transaction = db.transaction([STORE_NAME], 'readwrite');
+        const store = transaction.objectStore(STORE_NAME);
+        const request = store.put({ id, state });
+
+        request.onerror = (event) => {
+            console.error("DB: Error setting canvas state:", event.target.error);
+            reject("Error setting state.");
+        };
+
+        request.onsuccess = () => {
+            console.log(`DB: Set success for id: ${id}`);
+            resolve();
+        };
+    });
+}
+
+export async function removeCanvasState(id) {
+    console.log(`DB: Removing state for id: ${id}`);
+    const db = await openDB();
+    return new Promise((resolve, reject) => {
+        const transaction = db.transaction([STORE_NAME], 'readwrite');
+        const store = transaction.objectStore(STORE_NAME);
+        const request = store.delete(id);
+
+        request.onerror = (event) => {
+            console.error("DB: Error removing canvas state:", event.target.error);
+            reject("Error removing state.");
+        };
+
+        request.onsuccess = () => {
+            console.log(`DB: Remove success for id: ${id}`);
+            resolve();
+        };
+    });
+}