import json
import signal
import socket
import struct
import threading
from datetime import datetime

signal.signal(signal.SIGINT, signal.SIG_DFL)

PORT = 1234
HEADER_LENGTH = 2


def receive_fixed_length_msg(sock, msglen):
    message = b''
    while len(message) < msglen:
        chunk = sock.recv(msglen - len(message))  # preberi nekaj bajtov
        if chunk == b'':
            raise RuntimeError("socket connection broken")
        message = message + chunk  # pripni prebrane bajte sporocilu

    return message


def receive_json(sock) -> dict:
    # preberi glavo sporocila (v prvih 2 bytih je dolzina sporocila)
    header = receive_fixed_length_msg(sock, HEADER_LENGTH)
    message_length = struct.unpack("!H", header)[0]  # pretvori dolzino sporocila v int

    message = None
    if message_length > 0:  # ce je vse OK
        message = receive_fixed_length_msg(sock, message_length)  # preberi sporocilo
        message = message.decode("utf-8")
        message = json.loads(message)

    return message


def send_json(sock, message):
    message["time"] = datetime.now().strftime("%c")
    encoded_message = json.dumps(message).encode("utf-8")  # pretvori sporocilo v niz bajtov, uporabi UTF-8 kodno tabelo

    # ustvari glavo v prvih 2 bytih je dolzina sporocila (HEADER_LENGTH)
    # metoda pack "!H" : !=network byte order, H=unsigned short
    header = struct.pack("!H", len(encoded_message))

    message = header + encoded_message  # najprj posljemo dolzino sporocilo, slee nato sporocilo samo
    sock.sendall(message)


def send_error(sock, message):
    send_json(sock, {
        "type": "error",
        "data": message,
    })


# funkcija za komunikacijo z odjemalcem (tece v loceni niti za vsakega odjemalca)
def client_thread(client_sock, client_addr):
    global clients
    global usernames

    print("[system] connected with " + client_addr[0] + ":" + str(client_addr[1]))
    print("[system] we now have " + str(len(clients)) + " clients")

    try:

        while True:  # neskoncna zanka
            msg_received = receive_json(client_sock)
            msg_type = str(msg_received["type"])
            data = str(msg_received["data"])
            time = str(msg_received["time"])

            if not msg_received:  # ce obstaja sporocilo
                break

            match msg_type:
                case "username":
                    usernames[client_sock] = data

                case "message":
                    username = usernames[client_sock]
                    if username is None:
                        username = client_addr[0] + ":" + str(client_addr[1])
                    msg_received["username"] = username

                    print(f'[{time}] [{username}] : {data}')

                    if data.startswith("@"):
                        [username, *data] = data.split()
                        username = str(username).replace("@", "")

                        cl = [c for c, u in usernames.items() if u == username]
                        if len(cl) == 0:
                            send_error(client_sock, "Client with this username does not exist.")
                            continue
                        client = cl[0]

                        msg_received["data"] = "".join(data)
                        send_json(client, msg_received)
                        continue

                    for client in clients:
                        if client == client_sock:
                            continue
                        send_json(client, msg_received)

    except:
        # tule bi lahko bolj elegantno reagirali, npr. na posamezne izjeme. Trenutno kar pozremo izjemo
        pass

    # prisli smo iz neskoncne zanke
    with clients_lock:
        clients.remove(client_sock)
        if client_sock in usernames:
            usernames.pop(client_sock)

    print("[system] we now have " + str(len(clients)) + " clients")
    client_sock.close()


# kreiraj socket
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(("localhost", PORT))
server_socket.listen(1)

# cakaj na nove odjemalce
print("[system] listening ...")
clients = set()
usernames = dict()
clients_lock = threading.Lock()
while True:
    try:
        # pocakaj na novo povezavo - blokirajoc klic
        client_sock, client_addr = server_socket.accept()
        with clients_lock:
            clients.add(client_sock)

        thread = threading.Thread(target=client_thread, args=(client_sock, client_addr))
        thread.daemon = True
        thread.start()

    except KeyboardInterrupt:
        break

print("[system] closing server socket ...")
server_socket.close()