main.py

from pywebio import start_server
from pywebio.input import *
from pywebio.output import *
from pywebio.session import run_async, run_js

import asyncio

chat_msgs = []
online_users = set()

MAX_MESSAGES_COUNT = 100


async def main():
    global chat_msgs

    put_markdown("## 🧊 Welcome to our chat!\nThis project was made with Python within 100 lines of code!")

    msg_box = output()
    put_scrollable(msg_box, height=300, keep_bottom=True)

    nickname = await input("Enter chat", required=True, placeholder="Nickname", validate=lambda n: "This nickname is already in use!" if n in online_users or n == '📢' else None)
    online_users.add(nickname)

    chat_msgs.append(('📢', f"`{nickname}` joined chat!"))
    msg_box.append(put_markdown(f"`{nickname}` joined chat!"))

    refresh_task = run_async(refresh_msg(nickname, msg_box))

    while True:
        data = await input_group("💭 New message", [
            input(placeholder="Text of message", name="msg"),
            actions(name="cmd", buttons=["Send", {'label':"Quit chat", 'type':'cancel'}])
        ], validate=lambda m: ('msg', "Enter the text of message!") if m["cmd"] == "Send" and not m["msg"] else None)

        if data is None:
            break

        msg_box.append(put_markdown(f"`{nickname}`: {data['msg']}"))
        chat_msgs.append((nickname, data['msg']))

    # exit chat
    refresh_task.close()

    online_users.remove(nickname)
    toast("Вы вышли из чата!")
    msg_box.append(put_markdown(f"📢 `{nickname}` quited the chat !"))
    chat_msgs.append(('📢', f"`{nickname}` quited the chat!"))

    put_buttons(["Reenter"], onclick=lambda btn: run_js('window.location.reload()'))


async def refresh_msg(nickname, msg_box):
    global chat_msgs
    last_idx = len(chat_msgs)

    while True:
        await asyncio.sleep(1)

        for m in chat_msgs[last_idx:]:
            if m[0] != nickname:
                msg_box.append(put_markdown(f"`{m[0]}`: {m[1]}"))

        # remove expired
        if len(chat_msgs) > MAX_MESSAGES_COUNT:
            chat_msgs = chat_msgs[len(chat_msgs) // 2:]

        last_idx = len(chat_msgs)

if __name__ == "__main__":
    start_server(main, debug=True, port=8080, cdn=False)