Implement URL-safe Base64 encoding and optimize state initialization

Co-authored-by: sensslen <3428860+sensslen@users.noreply.github.com>

Author: Copilot

src/App.tsx

@@ -23,7 +23,8 @@ i18n.use(initReactI18next).init({
 
 const App: React.FC = () => {
   // Initialize URL from query parameter at component creation
-  const getInitialUrl = () => {
+  // Using lazy initialization to avoid calling getInitialUrl on every render
+  const [url, setUrl] = useState<string>(() => {
     const params = new URLSearchParams(window.location.search);
     const urlParam = params.get('url');
     if (urlParam) {
@@ -41,9 +42,7 @@ const App: React.FC = () => {
       }
     }
     return '';
-  };
-
-  const [url, setUrl] = useState<string>(getInitialUrl);
+  });
   const [error, setError] = useState<string | null>(null);
   const [success, setSuccess] = useState<string | null>(null);
   const { t } = useTranslation();

src/utils/urlEncoding.ts

@@ -1,30 +1,40 @@
 /**
- * Encodes a URL string to Base64 format for safe URL parameter usage
+ * Encodes a URL string to URL-safe Base64 format for safe URL parameter usage
+ * Uses URL-safe Base64 encoding (RFC 4648 §5) by replacing + with -, / with _, and removing padding =
  * @param url - The URL string to encode
- * @returns Base64 encoded string
+ * @returns URL-safe Base64 encoded string
  */
 export const encodeUrlToBase64 = (url: string): string => {
   try {
     // Use btoa for browser-compatible Base64 encoding
     // First encode to handle UTF-8 characters properly
     const utf8Bytes = new TextEncoder().encode(url);
     const binaryString = Array.from(utf8Bytes, byte => String.fromCharCode(byte)).join('');
-    return btoa(binaryString);
+    const base64 = btoa(binaryString);
+    // Convert to URL-safe Base64 by replacing + with -, / with _, and removing padding =
+    return base64.replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
   } catch (error) {
     console.error('Error encoding URL to Base64:', error);
     throw new Error('Failed to encode URL to Base64');
   }
 };
 
 /**
- * Decodes a Base64 encoded URL string
+ * Decodes a URL-safe Base64 encoded URL string
+ * Handles both URL-safe and standard Base64 formats
  * @param encodedUrl - The Base64 encoded URL string
  * @returns Decoded URL string
  */
 export const decodeBase64ToUrl = (encodedUrl: string): string => {
   try {
+    // Convert URL-safe Base64 back to standard Base64
+    let base64 = encodedUrl.replace(/-/g, '+').replace(/_/g, '/');
+    // Add padding if necessary
+    while (base64.length % 4 !== 0) {
+      base64 += '=';
+    }
     // Use atob for browser-compatible Base64 decoding
-    const binaryString = atob(encodedUrl);
+    const binaryString = atob(base64);
     const bytes = Uint8Array.from(binaryString, char => char.charCodeAt(0));
     return new TextDecoder().decode(bytes);
   } catch (error) {