server.py

from twisted.internet import reactor, protocol
from twisted.internet.protocol import ServerFactory as ServFactory, connectionDone
from twisted.internet.endpoints import TCP4ServerEndpoint
import json

# value, type


class Server(protocol.Protocol):
    def __init__(self, clients: dict, my_id):
        self.my_id = my_id
        self.clients = clients
        self.another_client = None

    def connectionMade(self):
        self.clients[self.my_id] = self

    @staticmethod
    def __encode_json(**kwargs):
        return json.dumps(kwargs)

    def send_message(self, **kwargs):
        if kwargs.get('where'):
            where = kwargs['where']
            del kwargs['where']
            where.transport.write(self.__encode_json(**kwargs).encode("utf-8"))
        else:
            self.transport.write(self.__encode_json(**kwargs).encode("utf-8"))

    def dataReceived(self, data):
        try:
            data = json.loads(data.decode("utf-8"))
        except UnicodeDecodeError:
            self.send_message(value="Cannot decode, use utf-8", type='error')
            return
        except json.JSONDecodeError:
            self.send_message(value="Cannot decode, use json", type='error')
            return

        if not data.get('type') or not data.get('value'):
            self.send_message(value=f"Wrong data", type='error')
            return

        if data['type'] == "user_choose":
            try:
                another_client = int(data['value'])
                if another_client in self.clients.keys():
                    self.another_client = another_client
                else:
                    raise KeyError

            except ValueError:
                self.send_message(value="Write another id as int", type='error')
            except KeyError:
                self.send_message(value="Can't find that client", type='error')
            else:
                self.send_message(value=f"Talk to {self.another_client}", type='user_chosen')

        elif data['type'] == "new_message":
            if not self.another_client:
                self.send_message(value=f"Don't have a client to send your message to", type='error')

            try:
                self.send_message(value=data['value'], where=self.clients[self.another_client], type='new_message')
            except KeyError:
                self.send_message(value="Something wrong happened, try another client", type='error')
                self.another_client = None

    def connectionLost(self, reason=connectionDone):
        self.disconnect()

    def disconnect(self):
        del self.clients[self.my_id]


class ServerFactory(ServFactory):
    def __init__(self):
        self.clients = {}
        self.last_id = 0

    def buildProtocol(self, addr):
        self.last_id += 1
        return Server(self.clients, self.last_id)


if __name__ == '__main__':
    endpoint = TCP4ServerEndpoint(reactor, 12345)
    endpoint.listen(ServerFactory())
    reactor.run()