import asyncio
import dataclasses
import logging
import os
from typing import Dict, List, Set

clients_by_nick: Dict[str, "Client"] = {}
all_channels: Dict[str, "Channel"] = {}


@dataclasses.dataclass
class Client:
    hostname: str
    reader: asyncio.StreamReader
    writer: asyncio.StreamWriter
    msg_queue: asyncio.Queue

    nickname: str = ""
    username: str = ""
    realname: str = ""
    registered: bool = False

    channels: Set[str] = dataclasses.field(default_factory=set)

    def id(self) -> str:
        return f"{self.nickname}!{self.username}@{self.hostname}"


@dataclasses.dataclass
class Channel:
    name: str
    clients_by_host: Dict[str, Client] = dataclasses.field(default_factory=dict)
    msg_queue: asyncio.Queue = dataclasses.field(default_factory=asyncio.Queue)


logging.basicConfig(
    format="%(asctime)s [%(levelname)s] - %(message)s", level=logging.INFO
)

logger = logging.getLogger()


async def handle_reader(client: Client) -> None:
    while True:
        raw_msg = await client.reader.readuntil(b"\r\n")
        if not raw_msg.endswith(b"\r\n"):
            raise RuntimeError("malformed message")
        msg = parse_irc_msg(raw_msg)
        await handle_irc_msg(client, msg)


async def handle_irc_msg(client: Client, msg: List[str]) -> None:
    if msg[0] == "CAP":
        # https://ircv3.net/specs/extensions/capability-negotiation.html
        logging.warning("TODO: implement support for client capability negotiation")
    elif msg[0] == "NICK":
        assert_argc(msg, 2)
        if client.nickname:
            del clients_by_nick[client.nickname]
        client.nickname = msg[1]
        clients_by_nick[client.nickname] = client
        if client.username and client.realname:
            client.registered = True
            logging.info(f"{client.hostname} ({client.id()}) registered")
    elif msg[0] == "USER":
        assert_argc(msg, 5)
        if client.registered:
            raise RuntimeError("USER command issued after registration")
        client.username = msg[1]
        client.realname = msg[4]
        if client.nickname:
            client.registered = True
            logging.info(f"{client.hostname} ({client.id()}) registered")
    elif msg[0] == "JOIN":
        assert_argc(msg, 2)
        assert_registered(client, msg)
        if not msg[1].startswith("#"):
            raise RuntimeError("invalid channel name")
        if msg[1] not in all_channels:
            all_channels[msg[1]] = Channel(name=msg[1])
            asyncio.create_task(process_channel(all_channels[msg[1]]))
        channel = all_channels[msg[1]]
        client.channels.add(channel.name)
        channel.clients_by_host[client.hostname] = client
        logging.info(f"{client.hostname} ({client.id()}) joined {msg[1]}")
        await channel.msg_queue.put(
            f":{client.nickname} JOIN {msg[1]}\r\n".encode("utf-8")
        )
    elif msg[0] == "PRIVMSG":
        assert_argc(msg, 3)
        assert_registered(client, msg)
        await privmsg(client, msg[1], msg[2])
    else:
        logging.warning(f"unsupported message {msg[0]}")


async def privmsg(client: Client, recipient: str, raw_msg: str) -> None:
    msg = f":{client.nickname} PRIVMSG {recipient} :{raw_msg}\r\n".encode("utf-8")

    for name, other_client in clients_by_nick.items():
        if name == recipient:
            other_client.msg_queue.put_nowait(msg)
            return

    for name, channel in all_channels.items():
        if name == recipient:
            channel.msg_queue.put_nowait(msg)
            return

    raise RuntimeError(f"unknown recipient {recipient}")


async def process_channel(channel: Channel) -> None:
    while True:
        msg = await channel.msg_queue.get()
        for client in channel.clients_by_host.values():
            if msg.startswith(f":{client.nickname} PRIVMSG".encode("utf-8")):
                continue
            client.msg_queue.put_nowait(msg)


def assert_registered(client: Client, msg: List[str]) -> None:
    if client.registered:
        return
    raise RuntimeError(f"{msg[0]} command issued before client fully registered")


def assert_argc(xs: List[str], i: int) -> None:
    if len(xs) == i:
        return
    raise RuntimeError(f"{xs[0]} had {len(xs)} arguments (expected {i})")


def parse_irc_msg(raw_msg: str) -> List[str]:
    tokens: List[str] = []
    raw_tokens: List[str] = raw_msg.decode("utf-8").split(" ")

    for i, token in enumerate(raw_tokens):
        if token.startswith(":"):
            trailing = token[1:] + " ".join(raw_tokens[i + 1 :])
            tokens.append(trailing)
            break
        tokens.append(token)

    if len(tokens) > 0:
        tokens[-1] = tokens[-1].strip()
    else:
        raise RuntimeError("empty message")

    return tokens


async def handle_writer(client: Client) -> None:
    while True:
        msg = await client.msg_queue.get()
        client.writer.write(msg)
        await client.writer.drain()


async def register_client(reader, writer):
    client = Client(
        hostname=writer.get_extra_info("peername")[0],
        reader=reader,
        writer=writer,
        msg_queue=asyncio.Queue(),
    )
    asyncio.create_task(handle_reader(client))
    asyncio.create_task(handle_writer(client))


async def main():
    bind_addr = os.getenv("BIND_ADDR") or "0.0.0.0"
    port = os.getenv("PORT") or 6667

    server = await asyncio.start_server(
        register_client,
        bind_addr,
        port,
        reuse_port=True,
    )

    logger.info(f"Listening on {bind_addr}:{port}...")
    async with server:
        await server.serve_forever()


if __name__ == "__main__":
    asyncio.run(main())