server.py

from flask import Flask, render_template, request
from flask_socketio import SocketIO, emit, join_room, leave_room
from re import match

app = Flask(__name__)
app.secret_key = 'secret!'
socketio = SocketIO(app, secret_key='secret!')

active_rooms = {}

def parse_string(string):
    # the + in the following regex ensures that the string is non-empty
    allowed_characters = r'^[a-zA-Z0-9_\-]+$'

    return (match(allowed_characters, string) is not None) and (len(string) <= 20)

@app.route('/', methods=['GET', 'POST'])
def index():
    return render_template('index.html')

@app.route('/chat/<room>')
def chat(room):
    username = request.cookies.get('username', 'Guest')
    user_list = active_rooms[room]
    return render_template('chat.html', room=room, username=username, user_list=user_list)

# To render list of actives room on the home page
@socketio.on('connect')
def send_active_rooms():
    active_room_names = list(active_rooms.keys())
    emit('send_active_rooms', active_room_names)

@socketio.on('attempt_join')
def handle_join_attempt(data):
    room = data['room']
    username = data['username']
    new_room = data['new_room']

    permitted_username = parse_string(username)
    permitted_room_name = parse_string(room)

    if not permitted_username or not permitted_room_name:
        warning = 'Names must be 20 characters or less and may only contain letters, numbers, hyphens, and underscores'
        emit('warning', {'warning': warning, 'room': room})
    else:
        if not new_room:
            if username in active_rooms[room]:
                warning = f'The username {username} already exists in {room}'
                emit('warning', {'warning': warning, 'room': room})
            else:
                active_rooms[room].append(username)
                emit('succesful_join', {'username': username, 'room': room})
        else:
            if room in active_rooms:
                warning = 'There is already an active room with this name'
                emit('warning', {'warning': warning, 'room': room})
            else:
                active_rooms[room] = [username]
                emit('succesful_join', {'username': username, 'room': room})


@socketio.on('join_socket_room')
def join_socket_room(data):
    room = data['room']
    username = data['username']
    join_room(room)
    emit('broadcast_user_info', {'username': username, 'dir': 'joined'}, to=room)

@socketio.on('message')
def handle_message(data):
    room = data['room']
    username = data['username']
    message = data['message']

    emit('update_chat', {'username': username, 'message': message}, to=room)

@socketio.on('leave_room')
def handle_leave_room(data):
    room = data['room']
    username = data['username']
    print(f'{username} is leaving room {room}')
    leave_room(room)
    active_rooms[room].remove(username)

    emit('broadcast_user_info', {'username': username, 'dir': 'left'}, to=room)

    # Automatically delete room with no active users
    if len(active_rooms[room]) == 0:
        del active_rooms[room]


if __name__ == '__main__':
    socketio.run(app, debug=True)