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.gitignore

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+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+env/
+venv/
+ENV/
+.venv
+*.egg-info/
+dist/
+build/
+
+# File locks
+*.lock
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Logs
+*.log

.replit

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+modules = ["python-3.11"]
+[agent]
+expertMode = true
+integrations = ["javascript_websocket:1.0.0"]
+
+[workflows]
+runButton = "Project"
+
+[[workflows.workflow]]
+name = "Project"
+mode = "parallel"
+author = "agent"
+
+[[workflows.workflow.tasks]]
+task = "workflow.run"
+args = "run"
+
+[[workflows.workflow]]
+name = "run"
+author = "agent"
+
+[[workflows.workflow.tasks]]
+task = "shell.exec"
+args = "python app.py"
+waitForPort = 5000
+
+[workflows.workflow.metadata]
+outputType = "webview"
+
+[[ports]]
+localPort = 5000
+externalPort = 80
+
+[[ports]]
+localPort = 33559
+externalPort = 3000

README.md

@@ -1,11 +1,244 @@
----
-title: Whatsapp
-emoji: 🔥
-colorFrom: pink
-colorTo: red
-sdk: docker
-pinned: false
-license: mit
----
-
-Check out the configuration reference at https://huggingface.co/docs/hub/spaces-config-reference
+# WhatsApp-like Web Chat Application
+
+A real-time messaging web application built with Flask-SocketIO and vanilla JavaScript, featuring WebSocket-based instant messaging with persistent JSON storage.
+
+## Features
+
+✅ **User Registration & Authentication**
+- Generate unique 8-digit user IDs
+- Token-based authentication
+- Session persistence with localStorage
+
+✅ **Real-time Messaging**
+- WebSocket-powered instant message delivery
+- Message history persistence in JSON files
+- Thread-safe file operations with locking
+
+✅ **Message Status Lifecycle**
+- ✓ Sent (single check)
+- ✓✓ Delivered (double check, gray)
+- ✓✓ Read (double check, blue)
+
+✅ **Rich Chat Features**
+- Typing indicators
+- Online/offline presence
+- Unread message badges
+- Contact management (add by 8-digit ID)
+
+✅ **Responsive UI**
+- WhatsApp-inspired design
+- Dark theme
+- Mobile-friendly layout
+
+## Project Structure
+
+```
+.
+├── app.py                  # Flask-SocketIO backend server
+├── requirements.txt        # Python dependencies
+├── data/
+│   ├── users.json         # User data storage
+│   └── messages.json      # Message history storage
+├── templates/
+│   └── index.html         # Frontend application
+└── test_app.py            # Automated test script
+```
+
+## Data Formats
+
+### users.json
+```json
+{
+  "12345678": {
+    "name": "Alice Demo",
+    "email": "alice@demo.com",
+    "token": "demo_token_alice_12345",
+    "contacts": ["87654321"],
+    "created_at": "2025-01-01T10:00:00"
+  }
+}
+```
+
+### messages.json
+```json
+[
+  {
+    "message_id": "msg_demo_001",
+    "from": "12345678",
+    "to": "87654321",
+    "message": "Hey Bob! How are you?",
+    "timestamp": "2025-01-01T12:00:00",
+    "status": "read"
+  }
+]
+```
+
+## Running on Replit
+
+1. **The app is automatically configured to run on Replit**
+   - Just click the "Run" button
+   - The server will start on port 5000
+   - The webview will open automatically
+
+2. **Access the application**
+   - Click the webview pane to open the chat interface
+   - Or open the URL shown in the console
+
+## Manual Setup (Local Development)
+
+1. **Install dependencies**
+   ```bash
+   pip install -r requirements.txt
+   ```
+
+2. **Run the server**
+   ```bash
+   python app.py
+   ```
+
+3. **Access the application**
+   - Open your browser to `http://localhost:5000`
+
+## How to Use
+
+### 1. Register a New User
+- Enter your name and email
+- Click "Register"
+- **Save your 8-digit User ID and Token** (displayed after registration)
+- You'll be automatically logged in
+
+### 2. Login (Returning Users)
+- Click "Login" link
+- Enter your 8-digit User ID
+- Enter your token
+- Click "Login"
+
+### 3. Add Contacts
+- In the chat interface, enter another user's 8-digit ID
+- Click "Add" to add them to your contacts
+- They will appear in your contacts list
+
+### 4. Start Chatting
+- Click on a contact to open the chat
+- Type your message and press Enter or click send
+- See real-time message status updates
+- Watch for typing indicators when your contact is typing
+
+### 5. Demo Users (Pre-configured)
+You can login with these demo accounts:
+
+**Alice Demo**
+- User ID: `12345678`
+- Token: `demo_token_alice_12345`
+
+**Bob Demo**
+- User ID: `87654321`
+- Token: `demo_token_bob_67890`
+
+## Testing
+
+The project includes an automated test script that validates all features.
+
+**Note:** Test dependencies (`requests` and `python-socketio`) are included in `requirements.txt` and will be installed automatically.
+
+Run the automated test script:
+
+```bash
+python test_app.py
+```
+
+This will test:
+- User registration
+- User login
+- Adding contacts
+- Sending messages
+- Real-time WebSocket communication
+- Message status updates (sent → delivered → read)
+- Message persistence in JSON files
+
+## Technical Stack
+
+### Backend
+- **Flask** - Web framework
+- **Flask-SocketIO** - WebSocket support
+- **eventlet** - Async networking library
+- **filelock** - Thread-safe file operations
+
+### Frontend
+- **Vanilla JavaScript** - No frameworks
+- **Socket.IO Client** - WebSocket client
+- **HTML5 & CSS3** - Responsive UI
+
+### Data Storage
+- **JSON Files** - Persistent storage with file locking
+- No database required
+
+## Security Notes
+
+⚠️ **This is a demonstration project with simplified security:**
+
+- No password hashing (tokens are used instead)
+- Tokens stored in localStorage (not secure for production)
+- No HTTPS enforcement
+- No rate limiting
+- No input sanitization beyond basic HTML escaping
+
+**For production use, implement:**
+- Proper password hashing (bcrypt, argon2)
+- Secure session management
+- HTTPS/TLS encryption
+- Input validation and sanitization
+- Rate limiting and CSRF protection
+- Database instead of JSON files
+
+## Features Implemented
+
+- [x] User registration with 8-digit ID generation
+- [x] Token-based login
+- [x] Contact management (add by ID)
+- [x] Real-time messaging via WebSockets
+- [x] Message persistence in JSON files
+- [x] Message status tracking (sent/delivered/read)
+- [x] Typing indicators
+- [x] Online/offline presence
+- [x] Unread message badges
+- [x] Thread-safe file operations
+- [x] Responsive WhatsApp-like UI
+- [x] Logout functionality
+
+## API Endpoints
+
+### REST API
+- `POST /api/register` - Register new user
+- `POST /api/login` - Login user
+- `POST /api/contacts/add` - Add contact
+- `POST /api/contacts` - Get user's contacts
+- `POST /api/messages` - Get conversation messages
+
+### WebSocket Events
+- `authenticate` - Authenticate WebSocket connection
+- `send_message` - Send a message
+- `typing` - Send typing indicator
+- `mark_conversation_read` - Mark messages as read
+- `message_delivered` - Update message delivery status
+- `message_read` - Update message read status
+
+## Troubleshooting
+
+**Messages not appearing in real-time?**
+- Check browser console for WebSocket connection errors
+- Ensure both users are logged in
+- Refresh the page
+
+**Can't add contact?**
+- Verify the 8-digit ID is correct
+- Make sure the user exists (registered)
+- Can't add yourself as a contact
+
+**Data not persisting?**
+- Check that `data/` directory has write permissions
+- Ensure no other process is locking the JSON files
+
+## License
+
+This is a demonstration project for educational purposes.

app.py

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+from flask import Flask, request, jsonify, send_from_directory
+from flask_socketio import SocketIO, emit, join_room, leave_room
+import json
+import os
+import random
+import secrets
+from datetime import datetime
+from filelock import FileLock
+from functools import wraps
+
+app = Flask(__name__, static_folder='static', template_folder='templates')
+app.config['SECRET_KEY'] = os.environ.get('SESSION_SECRET', secrets.token_hex(32))
+socketio = SocketIO(app, cors_allowed_origins="*", async_mode='eventlet')
+
+DATA_DIR = 'data'
+USERS_FILE = os.path.join(DATA_DIR, 'users.json')
+MESSAGES_FILE = os.path.join(DATA_DIR, 'messages.json')
+USERS_LOCK = FileLock(f"{USERS_FILE}.lock")
+MESSAGES_LOCK = FileLock(f"{MESSAGES_FILE}.lock")
+
+active_users = {}
+
+def init_data_files():
+    os.makedirs(DATA_DIR, exist_ok=True)
+    
+    if not os.path.exists(USERS_FILE):
+        with USERS_LOCK:
+            with open(USERS_FILE, 'w') as f:
+                json.dump({}, f, indent=2)
+    
+    if not os.path.exists(MESSAGES_FILE):
+        with MESSAGES_LOCK:
+            with open(MESSAGES_FILE, 'w') as f:
+                json.dump([], f, indent=2)
+
+def read_json(file_path, lock):
+    with lock:
+        with open(file_path, 'r') as f:
+            return json.load(f)
+
+def write_json(file_path, data, lock):
+    with lock:
+        with open(file_path, 'w') as f:
+            json.dump(data, f, indent=2)
+
+def generate_user_id():
+    users = read_json(USERS_FILE, USERS_LOCK)
+    while True:
+        user_id = str(random.randint(10000000, 99999999))
+        if user_id not in users:
+            return user_id
+
+def generate_token():
+    return secrets.token_urlsafe(32)
+
+def generate_message_id():
+    return secrets.token_urlsafe(16)
+
+def get_user_by_token(token):
+    users = read_json(USERS_FILE, USERS_LOCK)
+    for user_id, user_data in users.items():
+        if user_data.get('token') == token:
+            return user_id, user_data
+    return None, None
+
+@app.route('/')
+def index():
+    return send_from_directory('templates', 'index.html')
+
+@app.route('/api/register', methods=['POST'])
+def register():
+    data = request.json
+    name = data.get('name', '').strip()
+    email = data.get('email', '').strip()
+    
+    if not name or not email:
+        return jsonify({'error': 'Name and email are required'}), 400
+    
+    users = read_json(USERS_FILE, USERS_LOCK)
+    
+    for user_data in users.values():
+        if user_data.get('email') == email:
+            return jsonify({'error': 'Email already registered'}), 400
+    
+    user_id = generate_user_id()
+    token = generate_token()
+    
+    users[user_id] = {
+        'name': name,
+        'email': email,
+        'token': token,
+        'contacts': [],
+        'created_at': datetime.now().isoformat()
+    }
+    
+    write_json(USERS_FILE, users, USERS_LOCK)
+    
+    return jsonify({
+        'user_id': user_id,
+        'token': token,
+        'name': name,
+        'email': email
+    })
+
+@app.route('/api/login', methods=['POST'])
+def login():
+    data = request.json
+    user_id = data.get('user_id', '').strip()
+    token = data.get('token', '').strip()
+    
+    if not user_id or not token:
+        return jsonify({'error': 'User ID and token are required'}), 400
+    
+    users = read_json(USERS_FILE, USERS_LOCK)
+    
+    if user_id not in users:
+        return jsonify({'error': 'Invalid user ID'}), 401
+    
+    user_data = users[user_id]
+    if user_data.get('token') != token:
+        return jsonify({'error': 'Invalid token'}), 401
+    
+    return jsonify({
+        'user_id': user_id,
+        'name': user_data['name'],
+        'email': user_data['email'],
+        'contacts': user_data.get('contacts', [])
+    })
+
+@app.route('/api/contacts/add', methods=['POST'])
+def add_contact():
+    data = request.json
+    token = data.get('token', '')
+    contact_id = data.get('contact_id', '').strip()
+    
+    user_id, user_data = get_user_by_token(token)
+    if not user_id:
+        return jsonify({'error': 'Unauthorized'}), 401
+    
+    if not contact_id:
+        return jsonify({'error': 'Contact ID is required'}), 400
+    
+    users = read_json(USERS_FILE, USERS_LOCK)
+    
+    if contact_id not in users:
+        return jsonify({'error': 'User not found'}), 404
+    
+    if contact_id == user_id:
+        return jsonify({'error': 'Cannot add yourself as contact'}), 400
+    
+    if contact_id in user_data.get('contacts', []):
+        return jsonify({'error': 'Contact already added'}), 400
+    
+    users[user_id]['contacts'] = users[user_id].get('contacts', []) + [contact_id]
+    write_json(USERS_FILE, users, USERS_LOCK)
+    
+    contact_data = users[contact_id]
+    return jsonify({
+        'contact_id': contact_id,
+        'name': contact_data['name'],
+        'email': contact_data['email']
+    })
+
+@app.route('/api/contacts', methods=['POST'])
+def get_contacts():
+    data = request.json
+    token = data.get('token', '')
+    
+    user_id, user_data = get_user_by_token(token)
+    if not user_id:
+        return jsonify({'error': 'Unauthorized'}), 401
+    
+    users = read_json(USERS_FILE, USERS_LOCK)
+    contacts = []
+    
+    for contact_id in user_data.get('contacts', []):
+        if contact_id in users:
+            contact = users[contact_id]
+            contacts.append({
+                'user_id': contact_id,
+                'name': contact['name'],
+                'email': contact['email'],
+                'online': contact_id in active_users
+            })
+    
+    return jsonify({'contacts': contacts})
+
+@app.route('/api/messages', methods=['POST'])
+def get_messages():
+    data = request.json
+    token = data.get('token', '')
+    contact_id = data.get('contact_id', '')
+    
+    user_id, user_data = get_user_by_token(token)
+    if not user_id:
+        return jsonify({'error': 'Unauthorized'}), 401
+    
+    all_messages = read_json(MESSAGES_FILE, MESSAGES_LOCK)
+    
+    conversation_messages = [
+        msg for msg in all_messages
+        if (msg['from'] == user_id and msg['to'] == contact_id) or
+           (msg['from'] == contact_id and msg['to'] == user_id)
+    ]
+    
+    conversation_messages.sort(key=lambda x: x['timestamp'])
+    
+    return jsonify({'messages': conversation_messages})
+
+@socketio.on('connect')
+def handle_connect():
+    print(f'Client connected: {request.sid}')
+
+@socketio.on('authenticate')
+def handle_authenticate(data):
+    token = data.get('token', '')
+    user_id, user_data = get_user_by_token(token)
+    
+    if user_id:
+        active_users[user_id] = request.sid
+        join_room(user_id)
+        
+        socketio.emit('user_status', {
+            'user_id': user_id,
+            'online': True
+        })
+        
+        emit('authenticated', {'success': True, 'user_id': user_id})
+        print(f'User {user_id} ({user_data["name"]}) authenticated')
+    else:
+        emit('authenticated', {'success': False, 'error': 'Invalid token'})
+
+@socketio.on('disconnect')
+def handle_disconnect(reason=None):
+    user_id = None
+    for uid, sid in active_users.items():
+        if sid == request.sid:
+            user_id = uid
+            break
+    
+    if user_id:
+        del active_users[user_id]
+        socketio.emit('user_status', {
+            'user_id': user_id,
+            'online': False
+        })
+        print(f'User {user_id} disconnected')
+
+@socketio.on('send_message')
+def handle_send_message(data):
+    token = data.get('token', '')
+    to_user_id = data.get('to', '')
+    message_text = data.get('message', '')
+    
+    user_id, user_data = get_user_by_token(token)
+    if not user_id:
+        emit('error', {'message': 'Unauthorized'})
+        return
+    
+    message_id = generate_message_id()
+    timestamp = datetime.now().isoformat()
+    
+    message = {
+        'message_id': message_id,
+        'from': user_id,
+        'to': to_user_id,
+        'message': message_text,
+        'timestamp': timestamp,
+        'status': 'sent'
+    }
+    
+    messages = read_json(MESSAGES_FILE, MESSAGES_LOCK)
+    messages.append(message)
+    write_json(MESSAGES_FILE, messages, MESSAGES_LOCK)
+    
+    emit('message_sent', message)
+    
+    if to_user_id in active_users:
+        message['status'] = 'delivered'
+        messages = read_json(MESSAGES_FILE, MESSAGES_LOCK)
+        for msg in messages:
+            if msg['message_id'] == message_id:
+                msg['status'] = 'delivered'
+                break
+        write_json(MESSAGES_FILE, messages, MESSAGES_LOCK)
+        
+        socketio.emit('new_message', message, room=to_user_id)
+        emit('message_status_update', {
+            'message_id': message_id,
+            'status': 'delivered'
+        })
+
+@socketio.on('message_delivered')
+def handle_message_delivered(data):
+    message_id = data.get('message_id', '')
+    
+    messages = read_json(MESSAGES_FILE, MESSAGES_LOCK)
+    for msg in messages:
+        if msg['message_id'] == message_id and msg['status'] == 'sent':
+            msg['status'] = 'delivered'
+            break
+    write_json(MESSAGES_FILE, messages, MESSAGES_LOCK)
+    
+    for msg in messages:
+        if msg['message_id'] == message_id:
+            from_user_id = msg['from']
+            if from_user_id in active_users:
+                socketio.emit('message_status_update', {
+                    'message_id': message_id,
+                    'status': 'delivered'
+                }, room=from_user_id)
+            break
+
+@socketio.on('message_read')
+def handle_message_read(data):
+    message_id = data.get('message_id', '')
+    
+    messages = read_json(MESSAGES_FILE, MESSAGES_LOCK)
+    for msg in messages:
+        if msg['message_id'] == message_id:
+            msg['status'] = 'read'
+            from_user_id = msg['from']
+            break
+    write_json(MESSAGES_FILE, messages, MESSAGES_LOCK)
+    
+    if from_user_id in active_users:
+        socketio.emit('message_status_update', {
+            'message_id': message_id,
+            'status': 'read'
+        }, room=from_user_id)
+
+@socketio.on('mark_conversation_read')
+def handle_mark_conversation_read(data):
+    token = data.get('token', '')
+    contact_id = data.get('contact_id', '')
+    
+    user_id, user_data = get_user_by_token(token)
+    if not user_id:
+        return
+    
+    messages = read_json(MESSAGES_FILE, MESSAGES_LOCK)
+    updated_message_ids = []
+    
+    for msg in messages:
+        if msg['from'] == contact_id and msg['to'] == user_id and msg['status'] != 'read':
+            msg['status'] = 'read'
+            updated_message_ids.append(msg['message_id'])
+    
+    write_json(MESSAGES_FILE, messages, MESSAGES_LOCK)
+    
+    if contact_id in active_users:
+        for msg_id in updated_message_ids:
+            socketio.emit('message_status_update', {
+                'message_id': msg_id,
+                'status': 'read'
+            }, room=contact_id)
+
+@socketio.on('typing')
+def handle_typing(data):
+    token = data.get('token', '')
+    to_user_id = data.get('to', '')
+    is_typing = data.get('typing', False)
+    
+    user_id, user_data = get_user_by_token(token)
+    if not user_id:
+        return
+    
+    if to_user_id in active_users:
+        socketio.emit('user_typing', {
+            'user_id': user_id,
+            'typing': is_typing
+        }, room=to_user_id)
+
+# Hugging Face Spaces compatibility
+if __name__ == '__main__':
+    init_data_files()
+    print("WhatsApp-like server starting on Hugging Face...")
+    print("Access the app at https://your-username-your-app-name.hf.space")
+    socketio.run(app, host='0.0.0.0', port=7860, debug=False)

data/messages.json

@@ -0,0 +1,90 @@
+[
+  {
+    "message_id": "msg_demo_001",
+    "from": "12345678",
+    "to": "87654321",
+    "message": "Hey Bob! How are you?",
+    "timestamp": "2025-01-01T12:00:00",
+    "status": "read"
+  },
+  {
+    "message_id": "msg_demo_002",
+    "from": "87654321",
+    "to": "12345678",
+    "message": "Hi Alice! I'm doing great, thanks!",
+    "timestamp": "2025-01-01T12:01:00",
+    "status": "read"
+  },
+  {
+    "message_id": "msg_demo_003",
+    "from": "12345678",
+    "to": "87654321",
+    "message": "Want to grab coffee later?",
+    "timestamp": "2025-01-01T12:02:00",
+    "status": "delivered"
+  },
+  {
+    "message_id": "u06O-1fCsAOtr_mfg-xw-Q",
+    "from": "13632423",
+    "to": "19871079",
+    "message": "hello",
+    "timestamp": "2025-11-03T10:26:44.253783",
+    "status": "read"
+  },
+  {
+    "message_id": "h2HYFDu-JherEGFujRayqA",
+    "from": "19871079",
+    "to": "13632423",
+    "message": "hello",
+    "timestamp": "2025-11-03T10:27:12.376759",
+    "status": "read"
+  },
+  {
+    "message_id": "i6SIp9RS_nXScmaPSar_4g",
+    "from": "19871079",
+    "to": "13632423",
+    "message": "who are you",
+    "timestamp": "2025-11-03T10:27:18.038752",
+    "status": "read"
+  },
+  {
+    "message_id": "ZGlv9Zg5JOGAVmogdLii-g",
+    "from": "13632423",
+    "to": "19871079",
+    "message": "i am fil\\ne",
+    "timestamp": "2025-11-03T10:27:24.204194",
+    "status": "read"
+  },
+  {
+    "message_id": "EOee-Nugk2aomXhsylODlg",
+    "from": "19871079",
+    "to": "13632423",
+    "message": "hello",
+    "timestamp": "2025-11-03T10:28:14.464749",
+    "status": "sent"
+  },
+  {
+    "message_id": "HlpNuvjFUb23XIgTjzfFqw",
+    "from": "13089813",
+    "to": "27739400",
+    "message": "Hello from automated test! \ud83d\udc4b",
+    "timestamp": "2025-11-03T10:29:42.199807",
+    "status": "read"
+  },
+  {
+    "message_id": "0l-NIELRxFVxvPNY_zQruQ",
+    "from": "19871079",
+    "to": "13632423",
+    "message": "hello",
+    "timestamp": "2025-11-03T10:29:57.738998",
+    "status": "sent"
+  },
+  {
+    "message_id": "8I36S7iw4T-IuB7NIxrZqg",
+    "from": "19871079",
+    "to": "13632423",
+    "message": "helloo",
+    "timestamp": "2025-11-03T10:30:15.790133",
+    "status": "sent"
+  }
+]

data/users.json

@@ -0,0 +1,92 @@
+{
+  "12345678": {
+    "name": "Alice Demo",
+    "email": "alice@demo.com",
+    "token": "demo_token_alice_12345",
+    "contacts": [
+      "87654321"
+    ],
+    "created_at": "2025-01-01T10:00:00"
+  },
+  "87654321": {
+    "name": "Bob Demo",
+    "email": "bob@demo.com",
+    "token": "demo_token_bob_67890",
+    "contacts": [
+      "12345678"
+    ],
+    "created_at": "2025-01-01T11:00:00"
+  },
+  "13632423": {
+    "name": "abdullah ali",
+    "email": "abdullahali1692011@gmail.com",
+    "token": "qRp-NX-lIxtrzTLgvix7tPcekwcZpRmbNnQbZuhYHI0",
+    "contacts": [
+      "19871079"
+    ],
+    "created_at": "2025-11-03T10:25:58.261817"
+  },
+  "19871079": {
+    "name": "abdullah alioo",
+    "email": "abdullahtechhub1692011@gmail.com",
+    "token": "hSoljCRQ3kXPmmbJ4p5KvQyNgBmVCkd5cKOCj9A_ljA",
+    "contacts": [
+      "13632423"
+    ],
+    "created_at": "2025-11-03T10:26:26.208882"
+  },
+  "76582281": {
+    "name": "Test User 1",
+    "email": "testuser1_1762165678@test.com",
+    "token": "xG-xphaNlNaE-N5lbnIKNBd-8mIMzlQ24PtH6o0LESk",
+    "contacts": [
+      "12642270"
+    ],
+    "created_at": "2025-11-03T10:27:59.011170"
+  },
+  "12642270": {
+    "name": "Test User 2",
+    "email": "testuser2_1762165678@test.com",
+    "token": "jK7dDrMu2tDC-a4UJlt0vwhicSTyWSnIakwpuTBlTgo",
+    "contacts": [
+      "76582281"
+    ],
+    "created_at": "2025-11-03T10:27:59.018040"
+  },
+  "83708392": {
+    "name": "Test User 1",
+    "email": "testuser1_1762165705@test.com",
+    "token": "NMcpfP6HRJeRsSmsepU1c5TDQiwsnOyaLGwhFy18Zuw",
+    "contacts": [
+      "50185049"
+    ],
+    "created_at": "2025-11-03T10:28:25.930877"
+  },
+  "50185049": {
+    "name": "Test User 2",
+    "email": "testuser2_1762165705@test.com",
+    "token": "dZpu351F6YqLCDDZBIszWhIelfPqFOts3jtMQCtJAyE",
+    "contacts": [
+      "83708392"
+    ],
+    "created_at": "2025-11-03T10:28:25.937104"
+  },
+  "13089813": {
+    "name": "Test User 1",
+    "email": "testuser1_1762165778@test.com",
+    "token": "g0AZN0ngTzX2fk9THw_6k3jVG-KvXkjIVzEuselYi2c",
+    "contacts": [
+      "27739400"
+    ],
+    "created_at": "2025-11-03T10:29:38.088862"
+  },
+  "27739400": {
+    "name": "Test User 2",
+    "email": "testuser2_1762165778@test.com",
+    "token": "R0fICIcyQRqKn9WTgiR82v-kwUZ5PiILwnOhmtx-RPg",
+    "contacts": [
+      "13089813"
+    ],
+    "created_at": "2025-11-03T10:29:38.095038"
+  }
+}

replit.md

@@ -0,0 +1,118 @@
+# WhatsApp-like Web Chat Application
+
+## Project Overview
+A real-time messaging web application built with Flask-SocketIO (backend) and vanilla JavaScript (frontend). Uses WebSocket for instant messaging and JSON files for persistent data storage.
+
+## Purpose
+Demonstration of a complete chat application with:
+- User registration and authentication
+- Real-time messaging
+- Message status tracking (sent/delivered/read)
+- Typing indicators and presence
+- Persistent storage without a database
+
+## Current State
+✅ Fully functional and tested
+✅ All features implemented and working
+✅ Automated test suite passing
+✅ Server running on port 5000
+✅ Ready for use
+
+## Recent Changes (Nov 3, 2025)
+- Initial implementation of complete chat system
+- Fixed WebSocket broadcast parameter bug
+- Fixed disconnect handler signature
+- Added test dependencies (requests, python-socketio, websocket-client)
+- All tests passing successfully
+
+## Project Architecture
+
+### Backend (app.py)
+- **Flask** web framework with **Flask-SocketIO** for WebSocket support
+- **eventlet** for async networking
+- **filelock** for thread-safe JSON operations
+- REST API endpoints for registration, login, contacts
+- WebSocket handlers for real-time messaging, typing, presence
+
+### Frontend (templates/index.html)
+- Vanilla JavaScript (no framework dependencies)
+- Socket.IO client for WebSocket communication
+- Responsive WhatsApp-inspired dark theme UI
+- Real-time message updates and status tracking
+
+### Data Storage (data/)
+- **users.json**: User profiles, tokens, contacts
+- **messages.json**: All messages with status
+- Thread-safe file locking ensures data integrity
+
+### Testing (test_app.py)
+- Automated test suite covering all features
+- Tests registration, login, contacts, messaging, status updates
+- Validates message persistence
+
+## Key Features Implemented
+1. ✅ User registration with unique 8-digit ID generation
+2. ✅ Token-based authentication (simplified for demo)
+3. ✅ Contact management (add by ID)
+4. ✅ Real-time messaging via WebSockets
+5. ✅ Message status lifecycle: sent → delivered → read
+6. ✅ Typing indicators
+7. ✅ Online/offline presence tracking
+8. ✅ Unread message badges
+9. ✅ Message persistence in JSON files
+10. ✅ Responsive UI with chat list and conversation view
+
+## Security Notes (Demo Limitations)
+⚠️ This is a demonstration project with simplified security:
+- No password hashing (tokens used instead)
+- Tokens stored in localStorage
+- No HTTPS enforcement
+- No rate limiting
+- Basic HTML escaping only
+
+For production use, implement proper security measures.
+
+## How to Use
+1. Click "Run" button (server auto-starts on port 5000)
+2. Register a new user or login with demo accounts:
+   - Alice: ID `12345678`, Token `demo_token_alice_12345`
+   - Bob: ID `87654321`, Token `demo_token_bob_67890`
+3. Add contacts by entering their 8-digit ID
+4. Start chatting!
+
+## Testing
+Run automated tests: `python test_app.py`
+
+## Dependencies
+See `requirements.txt` for full list:
+- Flask 3.0.0
+- Flask-SocketIO 5.3.5
+- eventlet 0.33.3
+- filelock 3.13.1
+- requests 2.31.0 (for tests)
+- python-socketio 5.14.3 (for tests)
+- websocket-client 1.6.4 (for tests)
+
+## File Structure
+```
+├── app.py                  # Backend server
+├── requirements.txt        # Python dependencies
+├── README.md              # User documentation
+├── test_app.py            # Automated tests
+├── .gitignore             # Git ignore patterns
+├── data/
+│   ├── users.json         # User data
+│   └── messages.json      # Message history
+└── templates/
+    └── index.html         # Frontend application
+```
+
+## Technical Notes
+- Server runs on 0.0.0.0:5000 for Replit compatibility
+- WebSocket uses Socket.IO v4 protocol
+- JSON files use file locking for concurrent access safety
+- Active users tracked in-memory for presence
+- Debug mode enabled (disable for production)
+
+## User Preferences
+None specified yet.

requirements.txt

@@ -0,0 +1,7 @@
+Flask==3.0.0
+Flask-SocketIO==5.3.5
+eventlet==0.33.3
+filelock==3.13.1
+requests==2.31.0
+python-socketio==5.14.3
+websocket-client==1.6.4

templates/index.html

@@ -0,0 +1,985 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>WhatsApp-like Chat</title>
+    <script src="https://cdn.socket.io/4.6.0/socket.io.min.js"></script>
+    <style>
+        * {
+            margin: 0;
+            padding: 0;
+            box-sizing: border-box;
+        }
+
+        body {
+            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
+            background: #111b21;
+            height: 100vh;
+            overflow: hidden;
+        }
+
+        .auth-container {
+            display: flex;
+            justify-content: center;
+            align-items: center;
+            height: 100vh;
+            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
+        }
+
+        .auth-box {
+            background: white;
+            padding: 40px;
+            border-radius: 10px;
+            box-shadow: 0 10px 40px rgba(0,0,0,0.2);
+            width: 400px;
+            max-width: 90%;
+        }
+
+        .auth-box h2 {
+            margin-bottom: 20px;
+            color: #333;
+            text-align: center;
+        }
+
+        .form-group {
+            margin-bottom: 20px;
+        }
+
+        .form-group label {
+            display: block;
+            margin-bottom: 5px;
+            color: #555;
+            font-weight: 500;
+        }
+
+        .form-group input {
+            width: 100%;
+            padding: 12px;
+            border: 2px solid #ddd;
+            border-radius: 5px;
+            font-size: 14px;
+            transition: border-color 0.3s;
+        }
+
+        .form-group input:focus {
+            outline: none;
+            border-color: #667eea;
+        }
+
+        .btn {
+            width: 100%;
+            padding: 12px;
+            background: #667eea;
+            color: white;
+            border: none;
+            border-radius: 5px;
+            font-size: 16px;
+            font-weight: 600;
+            cursor: pointer;
+            transition: background 0.3s;
+        }
+
+        .btn:hover {
+            background: #5568d3;
+        }
+
+        .toggle-auth {
+            text-align: center;
+            margin-top: 15px;
+            color: #666;
+        }
+
+        .toggle-auth a {
+            color: #667eea;
+            text-decoration: none;
+            font-weight: 600;
+        }
+
+        .error-msg {
+            background: #fee;
+            color: #c33;
+            padding: 10px;
+            border-radius: 5px;
+            margin-bottom: 15px;
+            font-size: 14px;
+        }
+
+        .success-msg {
+            background: #efe;
+            color: #3c3;
+            padding: 10px;
+            border-radius: 5px;
+            margin-bottom: 15px;
+            font-size: 14px;
+        }
+
+        .chat-container {
+            display: none;
+            height: 100vh;
+            background: #222e35;
+        }
+
+        .chat-layout {
+            display: flex;
+            height: 100%;
+        }
+
+        .sidebar {
+            width: 400px;
+            background: #111b21;
+            border-right: 1px solid #2a3942;
+            display: flex;
+            flex-direction: column;
+        }
+
+        .sidebar-header {
+            background: #202c33;
+            padding: 15px;
+            display: flex;
+            justify-content: space-between;
+            align-items: center;
+        }
+
+        .user-info {
+            color: #e9edef;
+            font-weight: 500;
+        }
+
+        .user-id-display {
+            font-size: 12px;
+            color: #8696a0;
+        }
+
+        .logout-btn {
+            background: #dc3545;
+            color: white;
+            border: none;
+            padding: 8px 16px;
+            border-radius: 5px;
+            cursor: pointer;
+            font-size: 14px;
+        }
+
+        .add-contact-section {
+            background: #202c33;
+            padding: 15px;
+            border-bottom: 1px solid #2a3942;
+        }
+
+        .add-contact-form {
+            display: flex;
+            gap: 10px;
+        }
+
+        .add-contact-input {
+            flex: 1;
+            padding: 10px;
+            border: 1px solid #2a3942;
+            border-radius: 5px;
+            background: #2a3942;
+            color: #e9edef;
+            font-size: 14px;
+        }
+
+        .add-contact-btn {
+            background: #00a884;
+            color: white;
+            border: none;
+            padding: 10px 20px;
+            border-radius: 5px;
+            cursor: pointer;
+            font-weight: 600;
+        }
+
+        .contacts-list {
+            flex: 1;
+            overflow-y: auto;
+        }
+
+        .contact-item {
+            padding: 15px;
+            border-bottom: 1px solid #2a3942;
+            cursor: pointer;
+            display: flex;
+            align-items: center;
+            transition: background 0.2s;
+        }
+
+        .contact-item:hover {
+            background: #202c33;
+        }
+
+        .contact-item.active {
+            background: #2a3942;
+        }
+
+        .contact-avatar {
+            width: 50px;
+            height: 50px;
+            border-radius: 50%;
+            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
+            display: flex;
+            align-items: center;
+            justify-content: center;
+            color: white;
+            font-weight: bold;
+            font-size: 20px;
+            margin-right: 15px;
+        }
+
+        .contact-info {
+            flex: 1;
+        }
+
+        .contact-name {
+            color: #e9edef;
+            font-weight: 500;
+            margin-bottom: 3px;
+        }
+
+        .contact-status {
+            font-size: 12px;
+            color: #8696a0;
+        }
+
+        .contact-status.online {
+            color: #00a884;
+        }
+
+        .unread-badge {
+            background: #00a884;
+            color: white;
+            border-radius: 50%;
+            width: 24px;
+            height: 24px;
+            display: flex;
+            align-items: center;
+            justify-content: center;
+            font-size: 12px;
+            font-weight: bold;
+        }
+
+        .chat-area {
+            flex: 1;
+            display: flex;
+            flex-direction: column;
+            background: #0b141a;
+        }
+
+        .chat-header {
+            background: #202c33;
+            padding: 15px 20px;
+            display: flex;
+            align-items: center;
+            border-bottom: 1px solid #2a3942;
+        }
+
+        .chat-header-info {
+            flex: 1;
+        }
+
+        .chat-partner-name {
+            color: #e9edef;
+            font-weight: 500;
+            margin-bottom: 3px;
+        }
+
+        .chat-partner-status {
+            font-size: 13px;
+            color: #8696a0;
+        }
+
+        .typing-indicator {
+            font-size: 13px;
+            color: #00a884;
+            display: none;
+        }
+
+        .messages-container {
+            flex: 1;
+            overflow-y: auto;
+            padding: 20px;
+            background-image: url('data:image/svg+xml;base64,PHN2ZyB3aWR0aD0iMTAwIiBoZWlnaHQ9IjEwMCIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIj48ZGVmcz48cGF0dGVybiBpZD0iYSIgcGF0dGVyblVuaXRzPSJ1c2VyU3BhY2VPblVzZSIgd2lkdGg9IjEwMCIgaGVpZ2h0PSIxMDAiPjxyZWN0IHdpZHRoPSIxMDAiIGhlaWdodD0iMTAwIiBmaWxsPSIjMGIxNDFhIi8+PHBhdGggZD0iTTUwIDUwbTAtMzVhMzUgMzUgMCAxIDAgNzAgMGEzNSAzNSAwIDEgMC03MCAwIiBzdHJva2U9IiMxMTFiMjEiIHN0cm9rZS13aWR0aD0iMC41IiBmaWxsPSJub25lIi8+PC9wYXR0ZXJuPjwvZGVmcz48cmVjdCB3aWR0aD0iMTAwJSIgaGVpZ2h0PSIxMDAlIiBmaWxsPSJ1cmwoI2EpIi8+PC9zdmc+');
+        }
+
+        .message {
+            margin-bottom: 12px;
+            display: flex;
+            animation: messageSlideIn 0.3s ease;
+        }
+
+        @keyframes messageSlideIn {
+            from {
+                opacity: 0;
+                transform: translateY(10px);
+            }
+            to {
+                opacity: 1;
+                transform: translateY(0);
+            }
+        }
+
+        .message.sent {
+            justify-content: flex-end;
+        }
+
+        .message-bubble {
+            max-width: 60%;
+            padding: 8px 12px;
+            border-radius: 8px;
+            position: relative;
+        }
+
+        .message.received .message-bubble {
+            background: #202c33;
+            color: #e9edef;
+        }
+
+        .message.sent .message-bubble {
+            background: #005c4b;
+            color: #e9edef;
+        }
+
+        .message-text {
+            margin-bottom: 5px;
+            word-wrap: break-word;
+        }
+
+        .message-meta {
+            display: flex;
+            justify-content: flex-end;
+            align-items: center;
+            gap: 5px;
+            font-size: 11px;
+            color: #8696a0;
+        }
+
+        .message-status {
+            font-size: 16px;
+        }
+
+        .status-sent {
+            color: #8696a0;
+        }
+
+        .status-delivered {
+            color: #8696a0;
+        }
+
+        .status-read {
+            color: #53bdeb;
+        }
+
+        .message-input-area {
+            background: #202c33;
+            padding: 15px;
+            display: flex;
+            gap: 10px;
+            align-items: center;
+        }
+
+        .message-input {
+            flex: 1;
+            padding: 12px 15px;
+            border: none;
+            border-radius: 8px;
+            background: #2a3942;
+            color: #e9edef;
+            font-size: 15px;
+            resize: none;
+            max-height: 100px;
+        }
+
+        .message-input:focus {
+            outline: none;
+        }
+
+        .send-btn {
+            background: #00a884;
+            color: white;
+            border: none;
+            width: 50px;
+            height: 50px;
+            border-radius: 50%;
+            cursor: pointer;
+            font-size: 20px;
+            display: flex;
+            align-items: center;
+            justify-content: center;
+            transition: background 0.2s;
+        }
+
+        .send-btn:hover {
+            background: #06cf9c;
+        }
+
+        .empty-chat {
+            display: flex;
+            flex-direction: column;
+            align-items: center;
+            justify-content: center;
+            height: 100%;
+            color: #8696a0;
+            text-align: center;
+            padding: 40px;
+        }
+
+        .empty-chat-icon {
+            font-size: 80px;
+            margin-bottom: 20px;
+            opacity: 0.3;
+        }
+
+        .empty-chat-text {
+            font-size: 18px;
+        }
+
+        ::-webkit-scrollbar {
+            width: 6px;
+        }
+
+        ::-webkit-scrollbar-track {
+            background: #111b21;
+        }
+
+        ::-webkit-scrollbar-thumb {
+            background: #2a3942;
+            border-radius: 3px;
+        }
+
+        ::-webkit-scrollbar-thumb:hover {
+            background: #374955;
+        }
+
+        @media (max-width: 768px) {
+            .sidebar {
+                width: 100%;
+            }
+            .chat-area {
+                position: absolute;
+                top: 0;
+                left: 0;
+                right: 0;
+                bottom: 0;
+                display: none;
+            }
+            .chat-area.mobile-visible {
+                display: flex;
+            }
+            .sidebar.mobile-hidden {
+                display: none;
+            }
+        }
+    </style>
+</head>
+<body>
+    <div id="authContainer" class="auth-container">
+        <div class="auth-box">
+            <div id="registerForm">
+                <h2>Register</h2>
+                <div id="authMessage"></div>
+                <div class="form-group">
+                    <label>Name</label>
+                    <input type="text" id="registerName" placeholder="Enter your name">
+                </div>
+                <div class="form-group">
+                    <label>Email</label>
+                    <input type="email" id="registerEmail" placeholder="Enter your email">
+                </div>
+                <button class="btn" onclick="register()">Register</button>
+                <div class="toggle-auth">
+                    Already have an account? <a href="#" onclick="toggleAuth('login'); return false;">Login</a>
+                </div>
+            </div>
+
+            <div id="loginForm" style="display: none;">
+                <h2>Login</h2>
+                <div id="loginMessage"></div>
+                <div class="form-group">
+                    <label>User ID (8 digits)</label>
+                    <input type="text" id="loginUserId" placeholder="Enter your 8-digit ID" maxlength="8">
+                </div>
+                <div class="form-group">
+                    <label>Token</label>
+                    <input type="text" id="loginToken" placeholder="Enter your token">
+                </div>
+                <button class="btn" onclick="login()">Login</button>
+                <div class="toggle-auth">
+                    Don't have an account? <a href="#" onclick="toggleAuth('register'); return false;">Register</a>
+                </div>
+            </div>
+        </div>
+    </div>
+
+    <div id="chatContainer" class="chat-container">
+        <div class="chat-layout">
+            <div class="sidebar" id="sidebar">
+                <div class="sidebar-header">
+                    <div>
+                        <div class="user-info" id="currentUserName">User</div>
+                        <div class="user-id-display">ID: <span id="currentUserId"></span></div>
+                    </div>
+                    <button class="logout-btn" onclick="logout()">Logout</button>
+                </div>
+                <div class="add-contact-section">
+                    <div class="add-contact-form">
+                        <input type="text" class="add-contact-input" id="addContactId" 
+                               placeholder="Enter 8-digit User ID" maxlength="8">
+                        <button class="add-contact-btn" onclick="addContact()">Add</button>
+                    </div>
+                </div>
+                <div class="contacts-list" id="contactsList"></div>
+            </div>
+
+            <div class="chat-area" id="chatArea">
+                <div class="empty-chat">
+                    <div class="empty-chat-icon">💬</div>
+                    <div class="empty-chat-text">Select a contact to start chatting</div>
+                </div>
+            </div>
+        </div>
+    </div>
+
+    <script>
+        let socket;
+        let currentUser = null;
+        let currentChat = null;
+        let contacts = [];
+        let unreadCounts = {};
+        let typingTimeout = null;
+
+        function toggleAuth(mode) {
+            if (mode === 'login') {
+                document.getElementById('registerForm').style.display = 'none';
+                document.getElementById('loginForm').style.display = 'block';
+                document.getElementById('authMessage').innerHTML = '';
+                document.getElementById('loginMessage').innerHTML = '';
+            } else {
+                document.getElementById('registerForm').style.display = 'block';
+                document.getElementById('loginForm').style.display = 'none';
+                document.getElementById('authMessage').innerHTML = '';
+                document.getElementById('loginMessage').innerHTML = '';
+            }
+        }
+
+        async function register() {
+            const name = document.getElementById('registerName').value.trim();
+            const email = document.getElementById('registerEmail').value.trim();
+            const msgDiv = document.getElementById('authMessage');
+
+            if (!name || !email) {
+                msgDiv.innerHTML = '<div class="error-msg">Please fill all fields</div>';
+                return;
+            }
+
+            try {
+                const response = await fetch('/api/register', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ name, email })
+                });
+
+                const data = await response.json();
+
+                if (response.ok) {
+                    msgDiv.innerHTML = `<div class="success-msg">
+                        Registration successful!<br>
+                        <strong>Your ID: ${data.user_id}</strong><br>
+                        <strong>Your Token: ${data.token}</strong><br>
+                        <small>Save these credentials to login</small>
+                    </div>`;
+                    localStorage.setItem('user_id', data.user_id);
+                    localStorage.setItem('token', data.token);
+                    
+                    setTimeout(() => {
+                        currentUser = data;
+                        initChat();
+                    }, 2000);
+                } else {
+                    msgDiv.innerHTML = `<div class="error-msg">${data.error}</div>`;
+                }
+            } catch (error) {
+                msgDiv.innerHTML = `<div class="error-msg">Registration failed: ${error.message}</div>`;
+            }
+        }
+
+        async function login() {
+            const user_id = document.getElementById('loginUserId').value.trim();
+            const token = document.getElementById('loginToken').value.trim();
+            const msgDiv = document.getElementById('loginMessage');
+
+            if (!user_id || !token) {
+                msgDiv.innerHTML = '<div class="error-msg">Please fill all fields</div>';
+                return;
+            }
+
+            try {
+                const response = await fetch('/api/login', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ user_id, token })
+                });
+
+                const data = await response.json();
+
+                if (response.ok) {
+                    localStorage.setItem('user_id', user_id);
+                    localStorage.setItem('token', token);
+                    currentUser = { user_id, token, ...data };
+                    initChat();
+                } else {
+                    msgDiv.innerHTML = `<div class="error-msg">${data.error}</div>`;
+                }
+            } catch (error) {
+                msgDiv.innerHTML = `<div class="error-msg">Login failed: ${error.message}</div>`;
+            }
+        }
+
+        function initChat() {
+            document.getElementById('authContainer').style.display = 'none';
+            document.getElementById('chatContainer').style.display = 'block';
+            document.getElementById('currentUserName').textContent = currentUser.name;
+            document.getElementById('currentUserId').textContent = currentUser.user_id;
+
+            initWebSocket();
+            loadContacts();
+        }
+
+        function initWebSocket() {
+            socket = io();
+
+            socket.on('connect', () => {
+                console.log('Connected to server');
+                socket.emit('authenticate', { token: currentUser.token });
+            });
+
+            socket.on('authenticated', (data) => {
+                if (data.success) {
+                    console.log('Authenticated successfully');
+                } else {
+                    alert('Authentication failed: ' + data.error);
+                    logout();
+                }
+            });
+
+            socket.on('user_status', (data) => {
+                updateContactStatus(data.user_id, data.online);
+            });
+
+            socket.on('new_message', (message) => {
+                if (currentChat && message.from === currentChat.user_id) {
+                    appendMessage(message, false);
+                    socket.emit('mark_conversation_read', {
+                        token: currentUser.token,
+                        contact_id: currentChat.user_id
+                    });
+                } else {
+                    unreadCounts[message.from] = (unreadCounts[message.from] || 0) + 1;
+                    updateContactsList();
+                }
+            });
+
+            socket.on('message_sent', (message) => {
+                appendMessage(message, true);
+            });
+
+            socket.on('message_status_update', (data) => {
+                updateMessageStatus(data.message_id, data.status);
+            });
+
+            socket.on('user_typing', (data) => {
+                if (currentChat && data.user_id === currentChat.user_id) {
+                    const typingIndicator = document.querySelector('.typing-indicator');
+                    if (typingIndicator) {
+                        typingIndicator.style.display = data.typing ? 'block' : 'none';
+                    }
+                }
+            });
+        }
+
+        async function loadContacts() {
+            try {
+                const response = await fetch('/api/contacts', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ token: currentUser.token })
+                });
+
+                const data = await response.json();
+                contacts = data.contacts || [];
+                updateContactsList();
+            } catch (error) {
+                console.error('Failed to load contacts:', error);
+            }
+        }
+
+        function updateContactsList() {
+            const list = document.getElementById('contactsList');
+            list.innerHTML = '';
+
+            contacts.forEach(contact => {
+                const item = document.createElement('div');
+                item.className = 'contact-item';
+                if (currentChat && currentChat.user_id === contact.user_id) {
+                    item.className += ' active';
+                }
+                
+                const initial = contact.name.charAt(0).toUpperCase();
+                const unreadCount = unreadCounts[contact.user_id] || 0;
+                const onlineStatus = contact.online ? 'online' : 'offline';
+
+                item.innerHTML = `
+                    <div class="contact-avatar">${initial}</div>
+                    <div class="contact-info">
+                        <div class="contact-name">${contact.name}</div>
+                        <div class="contact-status ${onlineStatus}">
+                            ${contact.online ? 'Online' : 'Offline'}
+                        </div>
+                    </div>
+                    ${unreadCount > 0 ? `<div class="unread-badge">${unreadCount}</div>` : ''}
+                `;
+
+                item.onclick = () => openChat(contact);
+                list.appendChild(item);
+            });
+        }
+
+        function updateContactStatus(userId, online) {
+            const contact = contacts.find(c => c.user_id === userId);
+            if (contact) {
+                contact.online = online;
+                updateContactsList();
+                
+                if (currentChat && currentChat.user_id === userId) {
+                    const statusEl = document.querySelector('.chat-partner-status');
+                    if (statusEl && !statusEl.classList.contains('typing-indicator')) {
+                        statusEl.textContent = online ? 'Online' : 'Offline';
+                    }
+                }
+            }
+        }
+
+        async function addContact() {
+            const contactId = document.getElementById('addContactId').value.trim();
+            
+            if (!contactId || contactId.length !== 8) {
+                alert('Please enter a valid 8-digit User ID');
+                return;
+            }
+
+            try {
+                const response = await fetch('/api/contacts/add', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ 
+                        token: currentUser.token,
+                        contact_id: contactId 
+                    })
+                });
+
+                const data = await response.json();
+
+                if (response.ok) {
+                    document.getElementById('addContactId').value = '';
+                    loadContacts();
+                    alert(`Contact added: ${data.name}`);
+                } else {
+                    alert(data.error);
+                }
+            } catch (error) {
+                alert('Failed to add contact: ' + error.message);
+            }
+        }
+
+        async function openChat(contact) {
+            currentChat = contact;
+            unreadCounts[contact.user_id] = 0;
+            updateContactsList();
+
+            const chatArea = document.getElementById('chatArea');
+            chatArea.innerHTML = `
+                <div class="chat-header">
+                    <div class="chat-header-info">
+                        <div class="chat-partner-name">${contact.name}</div>
+                        <div class="chat-partner-status">${contact.online ? 'Online' : 'Offline'}</div>
+                        <div class="typing-indicator">typing...</div>
+                    </div>
+                </div>
+                <div class="messages-container" id="messagesContainer"></div>
+                <div class="message-input-area">
+                    <textarea class="message-input" id="messageInput" 
+                              placeholder="Type a message" rows="1"></textarea>
+                    <button class="send-btn" onclick="sendMessage()">▶</button>
+                </div>
+            `;
+
+            chatArea.classList.add('mobile-visible');
+            document.getElementById('sidebar').classList.add('mobile-hidden');
+
+            const messageInput = document.getElementById('messageInput');
+            messageInput.addEventListener('input', handleTyping);
+            messageInput.addEventListener('keypress', (e) => {
+                if (e.key === 'Enter' && !e.shiftKey) {
+                    e.preventDefault();
+                    sendMessage();
+                }
+            });
+
+            await loadMessages(contact.user_id);
+            
+            socket.emit('mark_conversation_read', {
+                token: currentUser.token,
+                contact_id: contact.user_id
+            });
+        }
+
+        async function loadMessages(contactId) {
+            try {
+                const response = await fetch('/api/messages', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ 
+                        token: currentUser.token,
+                        contact_id: contactId 
+                    })
+                });
+
+                const data = await response.json();
+                const messages = data.messages || [];
+
+                messages.forEach(msg => {
+                    const isSent = msg.from === currentUser.user_id;
+                    appendMessage(msg, isSent);
+                });
+
+                scrollToBottom();
+            } catch (error) {
+                console.error('Failed to load messages:', error);
+            }
+        }
+
+        function appendMessage(message, isSent) {
+            const container = document.getElementById('messagesContainer');
+            if (!container) return;
+
+            const msgDiv = document.createElement('div');
+            msgDiv.className = `message ${isSent ? 'sent' : 'received'}`;
+            msgDiv.dataset.messageId = message.message_id;
+
+            const time = new Date(message.timestamp).toLocaleTimeString('en-US', {
+                hour: '2-digit',
+                minute: '2-digit'
+            });
+
+            const statusIcon = getStatusIcon(message.status);
+
+            msgDiv.innerHTML = `
+                <div class="message-bubble">
+                    <div class="message-text">${escapeHtml(message.message)}</div>
+                    <div class="message-meta">
+                        <span>${time}</span>
+                        ${isSent ? `<span class="message-status">${statusIcon}</span>` : ''}
+                    </div>
+                </div>
+            `;
+
+            container.appendChild(msgDiv);
+            scrollToBottom();
+        }
+
+        function getStatusIcon(status) {
+            if (status === 'sent') return '<span class="status-sent">✓</span>';
+            if (status === 'delivered') return '<span class="status-delivered">✓✓</span>';
+            if (status === 'read') return '<span class="status-read">✓✓</span>';
+            return '';
+        }
+
+        function updateMessageStatus(messageId, status) {
+            const msgDiv = document.querySelector(`[data-message-id="${messageId}"]`);
+            if (msgDiv) {
+                const statusSpan = msgDiv.querySelector('.message-status');
+                if (statusSpan) {
+                    statusSpan.innerHTML = getStatusIcon(status);
+                }
+            }
+        }
+
+        function sendMessage() {
+            const input = document.getElementById('messageInput');
+            const message = input.value.trim();
+
+            if (!message || !currentChat) return;
+
+            socket.emit('send_message', {
+                token: currentUser.token,
+                to: currentChat.user_id,
+                message: message
+            });
+
+            input.value = '';
+            input.style.height = 'auto';
+            
+            socket.emit('typing', {
+                token: currentUser.token,
+                to: currentChat.user_id,
+                typing: false
+            });
+        }
+
+        function handleTyping() {
+            if (!currentChat) return;
+
+            socket.emit('typing', {
+                token: currentUser.token,
+                to: currentChat.user_id,
+                typing: true
+            });
+
+            clearTimeout(typingTimeout);
+            typingTimeout = setTimeout(() => {
+                socket.emit('typing', {
+                    token: currentUser.token,
+                    to: currentChat.user_id,
+                    typing: false
+                });
+            }, 1000);
+        }
+
+        function scrollToBottom() {
+            const container = document.getElementById('messagesContainer');
+            if (container) {
+                container.scrollTop = container.scrollHeight;
+            }
+        }
+
+        function escapeHtml(text) {
+            const map = {
+                '&': '&amp;',
+                '<': '&lt;',
+                '>': '&gt;',
+                '"': '&quot;',
+                "'": '&#039;'
+            };
+            return text.replace(/[&<>"']/g, m => map[m]);
+        }
+
+        function logout() {
+            localStorage.removeItem('user_id');
+            localStorage.removeItem('token');
+            if (socket) socket.disconnect();
+            location.reload();
+        }
+
+        window.onload = () => {
+            const savedUserId = localStorage.getItem('user_id');
+            const savedToken = localStorage.getItem('token');
+
+            if (savedUserId && savedToken) {
+                document.getElementById('loginUserId').value = savedUserId;
+                document.getElementById('loginToken').value = savedToken;
+            }
+        };
+    </script>
+</body>
+</html>

test_app.py

@@ -0,0 +1,261 @@
+#!/usr/bin/env python3
+"""
+Test script for WhatsApp-like chat application
+Demonstrates: Register → Login → Add Contact → Send Message → Status Updates
+"""
+
+import requests
+import time
+import json
+from socketio import SimpleClient
+
+BASE_URL = 'http://localhost:5000'
+
+def print_step(step, message):
+    print(f"\n{'='*60}")
+    print(f"STEP {step}: {message}")
+    print('='*60)
+
+def test_registration():
+    print_step(1, "Testing User Registration")
+    
+    user1_data = {
+        'name': 'Test User 1',
+        'email': f'testuser1_{int(time.time())}@test.com'
+    }
+    
+    user2_data = {
+        'name': 'Test User 2',
+        'email': f'testuser2_{int(time.time())}@test.com'
+    }
+    
+    print("\n📝 Registering User 1...")
+    response1 = requests.post(f'{BASE_URL}/api/register', json=user1_data)
+    user1 = response1.json()
+    print(f"✅ User 1 registered successfully!")
+    print(f"   Name: {user1['name']}")
+    print(f"   ID: {user1['user_id']}")
+    print(f"   Token: {user1['token'][:20]}...")
+    
+    print("\n📝 Registering User 2...")
+    response2 = requests.post(f'{BASE_URL}/api/register', json=user2_data)
+    user2 = response2.json()
+    print(f"✅ User 2 registered successfully!")
+    print(f"   Name: {user2['name']}")
+    print(f"   ID: {user2['user_id']}")
+    print(f"   Token: {user2['token'][:20]}...")
+    
+    return user1, user2
+
+def test_login(user):
+    print_step(2, "Testing User Login")
+    
+    login_data = {
+        'user_id': user['user_id'],
+        'token': user['token']
+    }
+    
+    print(f"\n🔐 Logging in as {user['name']}...")
+    response = requests.post(f'{BASE_URL}/api/login', json=login_data)
+    result = response.json()
+    
+    if response.status_code == 200:
+        print(f"✅ Login successful!")
+        print(f"   User: {result['name']}")
+        print(f"   Email: {result['email']}")
+        return True
+    else:
+        print(f"❌ Login failed: {result.get('error')}")
+        return False
+
+def test_add_contact(user1, user2):
+    print_step(3, "Testing Add Contact")
+    
+    contact_data = {
+        'token': user1['token'],
+        'contact_id': user2['user_id']
+    }
+    
+    print(f"\n👥 {user1['name']} adding {user2['name']} as contact...")
+    response = requests.post(f'{BASE_URL}/api/contacts/add', json=contact_data)
+    
+    if response.status_code == 200:
+        result = response.json()
+        print(f"✅ Contact added successfully!")
+        print(f"   Contact Name: {result['name']}")
+        print(f"   Contact ID: {result['contact_id']}")
+        return True
+    else:
+        error = response.json().get('error')
+        print(f"❌ Failed to add contact: {error}")
+        return False
+
+def test_get_contacts(user):
+    print_step(4, "Testing Get Contacts")
+    
+    print(f"\n📋 Getting contacts for {user['name']}...")
+    response = requests.post(f'{BASE_URL}/api/contacts', 
+                            json={'token': user['token']})
+    
+    if response.status_code == 200:
+        result = response.json()
+        contacts = result['contacts']
+        print(f"✅ Retrieved {len(contacts)} contact(s):")
+        for contact in contacts:
+            print(f"   - {contact['name']} (ID: {contact['user_id']})")
+        return contacts
+    else:
+        print(f"❌ Failed to get contacts")
+        return []
+
+def test_websocket_messaging(user1, user2):
+    print_step(5, "Testing WebSocket Real-time Messaging")
+    
+    print("\n🔌 Connecting User 1 via WebSocket...")
+    client1 = SimpleClient()
+    client1.connect(BASE_URL)
+    client1.emit('authenticate', {'token': user1['token']})
+    
+    event = client1.receive(timeout=5)
+    if event[0] == 'authenticated' and event[1]['success']:
+        print("✅ User 1 authenticated via WebSocket")
+    
+    print("\n🔌 Connecting User 2 via WebSocket...")
+    client2 = SimpleClient()
+    client2.connect(BASE_URL)
+    client2.emit('authenticate', {'token': user2['token']})
+    
+    event = client2.receive(timeout=5)
+    if event[0] == 'authenticated' and event[1]['success']:
+        print("✅ User 2 authenticated via WebSocket")
+    
+    print("\n💬 User 1 sending message to User 2...")
+    test_message = "Hello from automated test! 👋"
+    client1.emit('send_message', {
+        'token': user1['token'],
+        'to': user2['user_id'],
+        'message': test_message
+    })
+    
+    time.sleep(1)
+    
+    print("\n📨 Checking for received messages...")
+    received_messages = []
+    
+    try:
+        while True:
+            event = client2.receive(timeout=2)
+            print(f"   Received event: {event[0]}")
+            
+            if event[0] == 'new_message':
+                msg = event[1]
+                received_messages.append(msg)
+                print(f"✅ Message received!")
+                print(f"   From: {msg['from']}")
+                print(f"   Message: {msg['message']}")
+                print(f"   Status: {msg['status']}")
+                
+                print(f"\n📖 User 2 marking message as read...")
+                client2.emit('mark_conversation_read', {
+                    'token': user2['token'],
+                    'contact_id': user1['user_id']
+                })
+                break
+    except:
+        pass
+    
+    time.sleep(1)
+    
+    print("\n🔄 Checking for status updates on User 1's side...")
+    try:
+        while True:
+            event = client1.receive(timeout=2)
+            if event[0] == 'message_status_update':
+                status_update = event[1]
+                print(f"✅ Status update received!")
+                print(f"   Message ID: {status_update['message_id']}")
+                print(f"   New Status: {status_update['status']}")
+                if status_update['status'] == 'read':
+                    print("\n✨ Message lifecycle complete: sent → delivered → read")
+                    break
+    except:
+        pass
+    
+    print("\n🔌 Disconnecting clients...")
+    client1.disconnect()
+    client2.disconnect()
+    
+    return len(received_messages) > 0
+
+def test_message_persistence(user1, user2):
+    print_step(6, "Testing Message Persistence")
+    
+    print(f"\n📚 Loading message history...")
+    response = requests.post(f'{BASE_URL}/api/messages', 
+                            json={
+                                'token': user1['token'],
+                                'contact_id': user2['user_id']
+                            })
+    
+    if response.status_code == 200:
+        result = response.json()
+        messages = result['messages']
+        print(f"✅ Retrieved {len(messages)} message(s) from JSON storage:")
+        for msg in messages[-3:]:
+            print(f"   [{msg['status']}] {msg['from'][:8]}... → {msg['to'][:8]}...: {msg['message'][:30]}")
+        return True
+    else:
+        print(f"❌ Failed to load messages")
+        return False
+
+def main():
+    print("\n" + "="*60)
+    print("WhatsApp-like Chat Application - Automated Test Suite")
+    print("="*60)
+    
+    try:
+        user1, user2 = test_registration()
+        time.sleep(1)
+        
+        test_login(user1)
+        time.sleep(1)
+        
+        test_add_contact(user1, user2)
+        test_add_contact(user2, user1)
+        time.sleep(1)
+        
+        test_get_contacts(user1)
+        time.sleep(1)
+        
+        test_websocket_messaging(user1, user2)
+        time.sleep(1)
+        
+        test_message_persistence(user1, user2)
+        
+        print("\n" + "="*60)
+        print("✅ ALL TESTS COMPLETED SUCCESSFULLY!")
+        print("="*60)
+        print("\n📋 Test Summary:")
+        print("   ✅ User Registration")
+        print("   ✅ User Login")
+        print("   ✅ Add Contact")
+        print("   ✅ Get Contacts")
+        print("   ✅ Real-time Messaging via WebSocket")
+        print("   ✅ Message Status Lifecycle (sent → delivered → read)")
+        print("   ✅ Message Persistence in JSON")
+        print("\n💡 You can now login with these test credentials:")
+        print(f"   User 1 ID: {user1['user_id']}")
+        print(f"   User 1 Token: {user1['token']}")
+        print(f"   User 2 ID: {user2['user_id']}")
+        print(f"   User 2 Token: {user2['token']}")
+        
+    except Exception as e:
+        print(f"\n❌ Test failed with error: {str(e)}")
+        import traceback
+        traceback.print_exc()
+
+if __name__ == '__main__':
+    print("\n⚠️  Make sure the server is running on http://localhost:5000")
+    print("Starting tests in 3 seconds...\n")
+    time.sleep(3)
+    main()