from __future__ import annotations

import asyncio
import contextlib
from dataclasses import dataclass, field

from .logging_utils import log_print as print
from .protocol import AUTH, PING, PONG, STATUS_ERR, STATUS_OK, UDP_RECV, UDP_SEND, Frame, decode_json, encode_json, read_frame, write_frame


class UdpRelayProtocol(asyncio.DatagramProtocol):
    def __init__(self, channel: "UdpRelayChannel", session_id: int, stream_id: int) -> None:
        self.channel = channel
        self.session_id = session_id
        self.stream_id = stream_id

    def datagram_received(self, data: bytes, _addr) -> None:
        self.channel.log_udp_reply(self.session_id, self.stream_id, len(data))
        self.channel.enqueue_send(Frame(UDP_RECV, self.session_id, self.stream_id, 0, 0, data))


@dataclass
class UdpRelaySession:
    session_id: int
    stream_id: int
    transport: asyncio.DatagramTransport | None = None
    host: str = ""
    port: int = 0
    family: int = 0


@dataclass
class UdpRelayChannel:
    reader: asyncio.StreamReader
    writer: asyncio.StreamWriter
    token: str
    udp_sessions: dict[tuple[int, int], UdpRelaySession] = field(default_factory=dict)
    closed: bool = False
    send_lock: asyncio.Lock = field(default_factory=asyncio.Lock)
    send_queue: asyncio.Queue[Frame | None] = field(default_factory=asyncio.Queue)
    send_task: asyncio.Task | None = None
    _logged_sessions: set[tuple[int, int]] = field(default_factory=set)

    async def run(self) -> None:
        try:
            self.send_task = asyncio.create_task(self._send_loop())
            auth = await read_frame(self.reader)
            if auth.kind != AUTH:
                return
            payload = decode_json(auth.payload) if auth.payload else {}
            if payload.get("token") != self.token:
                return
            await self.safe_send(Frame(AUTH, 0, 0, 0, STATUS_OK, encode_json({"status": "ok", "kind": payload.get("purpose", "normal"), "udp_only": True})))
            while True:
                frame = await read_frame(self.reader)
                await self.handle(frame)
        finally:
            await self.close()

    def enqueue_send(self, frame: Frame) -> None:
        if self.closed:
            return
        with contextlib.suppress(asyncio.QueueFull):
            self.send_queue.put_nowait(frame)

    async def _send_loop(self) -> None:
        try:
            while True:
                frame = await self.send_queue.get()
                if frame is None:
                    break
                ok = await self.safe_send(frame)
                if not ok:
                    break
        except asyncio.CancelledError:
            pass

    async def safe_send(self, frame: Frame) -> bool:
        if self.closed:
            return False
        try:
            async with self.send_lock:
                if self.closed:
                    return False
                await write_frame(self.writer, frame)
            return True
        except Exception:
            return False

    async def handle(self, frame: Frame) -> None:
        key = (frame.session_id, frame.stream_id)
        if frame.kind == PING:
            await self.safe_send(Frame(PONG, 0, 0, frame.seq, 0, b"pong"))
            return
        if frame.kind != UDP_SEND:
            return
        session = self.udp_sessions.get(key)
        meta = None
        payload = frame.payload
        if frame.packet_id > 0 and frame.packet_id <= len(frame.payload):
            try:
                meta = decode_json(frame.payload[: frame.packet_id])
                payload = frame.payload[frame.packet_id :]
            except Exception:
                if session is None:
                    return
        if session is None:
            if meta is None:
                return
            try:
                family = int(meta.get("family", 0)) or 0
                transport, _protocol = await asyncio.get_running_loop().create_datagram_endpoint(
                    lambda: UdpRelayProtocol(self, frame.session_id, frame.stream_id),
                    remote_addr=(meta["host"], int(meta["port"])),
                    family=family or 0,
                )
                session = UdpRelaySession(frame.session_id, frame.stream_id, transport, meta["host"], int(meta["port"]), family)
                self.udp_sessions[key] = session
                print(f"[relay] udp session opened session={frame.session_id} stream={frame.stream_id} target={meta['host']}:{int(meta['port'])}")
            except Exception as exc:
                await self.safe_send(Frame(UDP_RECV, frame.session_id, frame.stream_id, 0, STATUS_ERR, str(exc).encode()))
                return
        if session.transport is not None:
            with contextlib.suppress(Exception):
                session.transport.sendto(payload)

    def log_udp_reply(self, session_id: int, stream_id: int, size: int) -> None:
        key = (session_id, stream_id)
        if key in self._logged_sessions:
            return
        self._logged_sessions.add(key)
        print(f"[relay] udp reply session={session_id} stream={stream_id} bytes={size}")

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        self.send_queue.put_nowait(None)
        for session in self.udp_sessions.values():
            if session.transport:
                session.transport.close()
        self.udp_sessions.clear()
        if self.send_task and self.send_task is not asyncio.current_task():
            self.send_task.cancel()
            with contextlib.suppress(Exception):
                await self.send_task
        self.writer.close()
        with contextlib.suppress(Exception):
            await self.writer.wait_closed()


class UdpRelayServer:
    def __init__(self, token: str) -> None:
        self.token = token

    async def start(self, host: str, port: int) -> None:
        async def accept(reader: asyncio.StreamReader, writer: asyncio.StreamWriter) -> None:
            try:
                await UdpRelayChannel(reader, writer, self.token).run()
            except (asyncio.IncompleteReadError, ConnectionResetError, BrokenPipeError, OSError):
                pass

        print(f"[relay] udp server listening on {host}:{port}")
        server = await asyncio.start_server(accept, host, port)
        async with server:
            await server.serve_forever()