from __future__ import annotations

import asyncio
import contextlib
import itertools
import socket
import struct
from dataclasses import dataclass, field
from typing import Dict

from .config import Config, RelayNode
from .protocol import AUTH, STATUS_OK, TCP_CLOSE, TCP_DATA, TCP_OPEN, TCP_STATUS, UDP_RECV, UDP_SEND, Frame, decode_json, encode_json, read_frame, write_frame
from .scheduler import Scheduler

SOCKS_VERSION = 5


async def read_exact(reader: asyncio.StreamReader, size: int) -> bytes:
    return await reader.readexactly(size)


@dataclass(eq=False)
class RelayLink:
    node: RelayNode
    reader: asyncio.StreamReader
    writer: asyncio.StreamWriter
    pump: asyncio.Task | None = None
    tcp_sessions: Dict[tuple[int, int], "TcpRaceSession"] = field(default_factory=dict)
    udp_server: "UdpAssociateServer | None" = None
    closed: bool = False

    async def start(self) -> None:
        await write_frame(self.writer, Frame(AUTH, 0, 0, 0, 0, encode_json({"token": self.node.token})))
        frame = await read_frame(self.reader)
        if frame.kind != AUTH or frame.packet_id != STATUS_OK:
            raise ConnectionError(f"relay auth failed: {self.node.name}")
        self.pump = asyncio.create_task(self._pump())

    async def _pump(self) -> None:
        try:
            while True:
                frame = await read_frame(self.reader)
                key = (frame.session_id, frame.stream_id)
                if frame.kind in (TCP_STATUS, TCP_DATA, TCP_CLOSE):
                    session = self.tcp_sessions.get(key)
                    if session:
                        await session.handle_frame(self, frame)
                elif frame.kind == UDP_RECV and self.udp_server:
                    await self.udp_server.handle_from_relay(frame, self)
        except asyncio.IncompleteReadError:
            pass
        finally:
            await self.close()

    async def send(self, frame: Frame) -> None:
        if self.closed:
            raise ConnectionError(f"relay closed: {self.node.name}")
        await write_frame(self.writer, frame)

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        self.writer.close()
        with contextlib.suppress(Exception):
            await self.writer.wait_closed()


@dataclass
class UdpFlowState:
    flow_id: int
    client_addr: tuple[str, int]
    target_host: str
    target_port: int
    created_at: float
    last_activity: float
    packets_sent: int = 0
    packets_received: int = 0
    duplicate_responses: int = 0
    winner_name: str | None = None
    candidate_names: tuple[str, ...] = ()

    def touch(self, now: float) -> None:
        self.last_activity = now


@dataclass
class TcpRaceSession:
    session_id: int
    stream_id: int
    target_host: str
    target_port: int
    local_reader: asyncio.StreamReader
    local_writer: asyncio.StreamWriter
    links: list[RelayLink]
    warmup_bytes: int
    winning_link: RelayLink | None = None
    winner_name: str | None = None
    opened: int = 0
    open_errors: list[str] = field(default_factory=list)
    uplink_bytes: int = 0
    closed: bool = False
    open_event: asyncio.Event = field(default_factory=asyncio.Event)
    winner_event: asyncio.Event = field(default_factory=asyncio.Event)
    pump_task: asyncio.Task | None = None
    win_counts: Dict[str, int] = field(default_factory=dict)

    async def start(self) -> None:
        meta = encode_json({"host": self.target_host, "port": self.target_port})
        for link in self.links:
            link.tcp_sessions[(self.session_id, self.stream_id)] = self
            await link.send(Frame(TCP_OPEN, self.session_id, self.stream_id, 0, 0, meta))
        await asyncio.wait_for(self.open_event.wait(), timeout=10)
        if self.opened == 0:
            raise ConnectionError(self.open_errors[0] if self.open_errors else "all relays failed")
        self.pump_task = asyncio.create_task(self._pump_local())

    async def _pump_local(self) -> None:
        try:
            while True:
                chunk = await self.local_reader.read(65536)
                if not chunk:
                    break
                self.uplink_bytes += len(chunk)
                if self.winning_link is None and self.uplink_bytes <= self.warmup_bytes:
                    await asyncio.gather(*(link.send(Frame(TCP_DATA, self.session_id, self.stream_id, 0, 0, chunk)) for link in self.links if not link.closed), return_exceptions=True)
                else:
                    if self.winning_link is None:
                        await self.winner_event.wait()
                    if self.winning_link:
                        await self.winning_link.send(Frame(TCP_DATA, self.session_id, self.stream_id, 0, 0, chunk))
        except Exception:
            pass
        finally:
            await self.close()

    async def handle_frame(self, link: RelayLink, frame: Frame) -> None:
        if self.closed:
            return
        if frame.kind == TCP_STATUS:
            if frame.packet_id == STATUS_OK:
                self.opened += 1
            else:
                self.open_errors.append(frame.payload.decode("utf-8", errors="replace"))
            if self.opened > 0 or len(self.open_errors) == len(self.links):
                self.open_event.set()
            return
        if frame.kind == TCP_DATA:
            if self.winning_link is None:
                self.winning_link = link
                self.winner_name = link.node.name
                self.win_counts[link.node.name] = self.win_counts.get(link.node.name, 0) + 1
                node_total = self.win_counts[link.node.name]
                relay_detail = ", ".join(f"{name}={count}" for name, count in sorted(self.win_counts.items())) or "none"
                print(f"[edge] tcp win session={self.session_id} target={self.target_host}:{self.target_port} winner={link.node.name} node_total={node_total} win_breakdown={relay_detail}")
                self.winner_event.set()
                await self._close_losers(except_link=link)
            if link is self.winning_link:
                self.local_writer.write(frame.payload)
                await self.local_writer.drain()
            return
        if frame.kind == TCP_CLOSE:
            if self.winning_link is None:
                self.winning_link = link
                self.winner_event.set()
            if link is self.winning_link:
                await self.close()

    async def _close_losers(self, except_link: RelayLink) -> None:
        await asyncio.gather(*(link.send(Frame(TCP_CLOSE, self.session_id, self.stream_id, 0, 0, b"")) for link in self.links if link is not except_link and not link.closed), return_exceptions=True)

    async def close(self) -> None:
        if self.closed:
            return
        self.closed = True
        if self.pump_task and self.pump_task is not asyncio.current_task():
            self.pump_task.cancel()
            with contextlib.suppress(Exception):
                await self.pump_task
        await asyncio.gather(*(link.send(Frame(TCP_CLOSE, self.session_id, self.stream_id, 0, 0, b"")) for link in self.links if not link.closed), return_exceptions=True)
        for link in self.links:
            link.tcp_sessions.pop((self.session_id, self.stream_id), None)
        self.local_writer.close()
        with contextlib.suppress(Exception):
            await self.local_writer.wait_closed()


class UdpAssociateServer(asyncio.DatagramProtocol):
    def __init__(self, edge: "SocksEdge") -> None:
        self.edge = edge
        self.transport: asyncio.DatagramTransport | None = None
        self.client_addr = None
        self.packet_counter = itertools.count(1)
        self.pending: set[int] = set()
        self.packet_flows: dict[int, int] = {}
        self.client_flows: dict[tuple[tuple[str, int], str, int], UdpFlowState] = {}
        self.flow_counter = itertools.count(1)
        self.last_summary_at = 0.0
        self.win_counts: Dict[str, int] = {}

    def connection_made(self, transport) -> None:
        self.transport = transport

    def datagram_received(self, data: bytes, addr) -> None:
        if len(data) < 10:
            return
        if self.client_addr is None:
            self.client_addr = addr
            print(f"[edge] udp client bound addr={addr[0]}:{addr[1]}")
        if addr != self.client_addr:
            return
        host, port, payload = self._parse_socks_udp(data)
        loop = asyncio.get_running_loop()
        now = loop.time()
        flow_key = ((addr[0], addr[1]), host, port)
        flow = self.client_flows.get(flow_key)
        if flow is None:
            flow = UdpFlowState(
                flow_id=next(self.flow_counter),
                client_addr=(addr[0], addr[1]),
                target_host=host,
                target_port=port,
                created_at=now,
                last_activity=now,
            )
            self.client_flows[flow_key] = flow
        flow.touch(now)
        flow.packets_sent += 1
        packet_id = next(self.packet_counter)
        self.pending.add(packet_id)
        self.packet_flows[packet_id] = flow.flow_id
        print(f"[edge] udp recv flow={flow.flow_id} packet_id={packet_id} target={host}:{port} size={len(payload)}")
        asyncio.create_task(self.edge.forward_udp(host, port, payload, packet_id, self))
        self._log_udp_summary()

    async def handle_from_relay(self, frame: Frame, link: RelayLink) -> None:
        if frame.packet_id not in self.pending or self.transport is None or self.client_addr is None:
            return
        self.pending.discard(frame.packet_id)
        flow_id = self.packet_flows.pop(frame.packet_id, 0)
        host = self.edge.udp_targets.get(frame.packet_id, ("0.0.0.0", 0))[0]
        port = self.edge.udp_targets.get(frame.packet_id, ("0.0.0.0", 0))[1]
        packet = self._build_socks_udp(host, port, frame.payload)
        winner_log = ""
        flow = self._find_flow(flow_id)
        if flow is not None:
            now = asyncio.get_running_loop().time()
            flow.touch(now)
            flow.packets_received += 1
            if flow.winner_name is None:
                flow.winner_name = link.node.name
                self.win_counts[link.node.name] = self.win_counts.get(link.node.name, 0) + 1
                relay_detail = ", ".join(f"{name}={count}" for name, count in sorted(self.win_counts.items())) or "none"
                print(
                    f"[edge] udp flow={flow.flow_id} winner={link.node.name} "
                    f"target={flow.target_host}:{flow.target_port} mode=single candidates={len(flow.candidate_names) or len(self.edge.links)}"
                )
                print(f"[edge] udp win relay_breakdown={relay_detail}")
            elif flow.winner_name != link.node.name:
                flow.duplicate_responses += 1
                winner_log = f" duplicate=1 winner={flow.winner_name} from={link.node.name}"
        print(
            f"[edge] udp send flow={flow_id or 'unknown'} packet_id={frame.packet_id} "
            f"target={host}:{port} size={len(frame.payload)} relay={link.node.name}{winner_log}"
        )
        self.transport.sendto(packet, self.client_addr)
        self._log_udp_summary()

    def set_flow_candidates(self, packet_id: int, candidate_names: tuple[str, ...]) -> None:
        flow_id = self.packet_flows.get(packet_id)
        flow = self._find_flow(flow_id)
        if flow is not None and not flow.candidate_names:
            flow.candidate_names = candidate_names

    def note_unsent(self, packet_id: int) -> None:
        flow_id = self.packet_flows.pop(packet_id, 0)
        self.pending.discard(packet_id)
        flow = self._find_flow(flow_id)
        if flow is not None:
            flow.touch(asyncio.get_running_loop().time())
        print(f"[edge] udp drop flow={flow_id or 'unknown'} packet_id={packet_id} reason=no_available_links")
        self._log_udp_summary(force=True)

    def _find_flow(self, flow_id: int | None) -> UdpFlowState | None:
        if not flow_id:
            return None
        for flow in self.client_flows.values():
            if flow.flow_id == flow_id:
                return flow
        return None

    def _log_udp_summary(self, force: bool = False) -> None:
        now = asyncio.get_running_loop().time()
        if not force and now - self.last_summary_at < 10:
            return
        self.last_summary_at = now
        active_flows = len(self.client_flows)
        winners = sum(1 for flow in self.client_flows.values() if flow.winner_name)
        packets_sent = sum(flow.packets_sent for flow in self.client_flows.values())
        packets_received = sum(flow.packets_received for flow in self.client_flows.values())
        duplicates = sum(flow.duplicate_responses for flow in self.client_flows.values())
        print(
            f"[edge] udp summary bind={self.client_addr[0]}:{self.client_addr[1]} active_flows={active_flows} "
            f"winner_flows={winners} packets_sent={packets_sent} packets_received={packets_received} dup={duplicates}"
            if self.client_addr
            else f"[edge] udp summary bind=unbound active_flows={active_flows} winner_flows={winners} packets_sent={packets_sent} packets_received={packets_received} dup={duplicates}"
        )

    def _parse_socks_udp(self, packet: bytes) -> tuple[str, int, bytes]:
        atyp = packet[3]
        offset = 4
        if atyp == 1:
            host = socket.inet_ntoa(packet[offset:offset + 4])
            offset += 4
        elif atyp == 3:
            size = packet[offset]
            offset += 1
            host = packet[offset:offset + size].decode()
            offset += size
        else:
            raise ValueError("unsupported udp atyp")
        port = struct.unpack("!H", packet[offset:offset + 2])[0]
        offset += 2
        return host, port, packet[offset:]

    def _build_socks_udp(self, host: str, port: int, payload: bytes) -> bytes:
        try:
            addr = socket.inet_aton(host)
            header = b"\x00\x00\x00\x01" + addr + struct.pack("!H", port)
        except OSError:
            raw = host.encode()
            header = b"\x00\x00\x00\x03" + bytes([len(raw)]) + raw + struct.pack("!H", port)
        return header + payload


class SocksEdge:
    def __init__(self, listen_host: str, listen_port: int, config: Config) -> None:
        self.listen_host = listen_host
        self.listen_port = listen_port
        self.config = config
        self.scheduler = Scheduler(config)
        self.links: list[RelayLink] = []
        self.session_ids = itertools.count(1)
        self.udp_targets: dict[int, tuple[str, int]] = {}
        self.udp_server: UdpAssociateServer | None = None

    async def start(self) -> None:
        await self.scheduler.start()
        await self._connect_relays()
        server = await asyncio.start_server(self._accept, self.listen_host, self.listen_port)
        sockets = ", ".join(str(sock.getsockname()) for sock in server.sockets or [])
        print(f"[edge] socks5 listening on {sockets}")
        async with server:
            await server.serve_forever()

    async def _connect_relays(self) -> None:
        for node in self.config.relays:
            reader, writer = await asyncio.open_connection(node.host, node.port)
            link = RelayLink(node, reader, writer)
            await link.start()
            self.links.append(link)
        loop = asyncio.get_running_loop()
        transport, protocol = await loop.create_datagram_endpoint(lambda: UdpAssociateServer(self), local_addr=(self.listen_host, 0))
        self.udp_server = protocol
        for link in self.links:
            link.udp_server = protocol
        self.udp_transport = transport

    async def _accept(self, reader: asyncio.StreamReader, writer: asyncio.StreamWriter) -> None:
        try:
            peer = writer.get_extra_info("peername")
            host, port, udp_mode = await self._handshake(reader, writer, peer)
            if udp_mode:
                return
            links = self._selected_links()
            session = TcpRaceSession(
                session_id=next(self.session_ids),
                stream_id=0,
                target_host=host,
                target_port=port,
                local_reader=reader,
                local_writer=writer,
                links=links,
                warmup_bytes=self.config.tcp_warmup_bytes,
            )
            await session.start()
        except Exception:
            writer.close()
            with contextlib.suppress(Exception):
                await writer.wait_closed()

    def _selected_links(self) -> list[RelayLink]:
        chosen = {node.name for node in self.scheduler.choose()}
        links = [link for link in self.links if link.node.name in chosen and not link.closed]
        return links or [link for link in self.links if not link.closed][:1]

    async def forward_udp(self, host: str, port: int, payload: bytes, packet_id: int, udp_server: UdpAssociateServer) -> None:
        self.udp_targets[packet_id] = (host, port)
        meta = encode_json({"host": host, "port": port})
        links = self._selected_links()
        link_names = ",".join(link.node.name for link in links) or "none"
        udp_server.set_flow_candidates(packet_id, tuple(link.node.name for link in links))
        print(f"[edge] udp forward packet_id={packet_id} target={host}:{port} size={len(payload)} links={link_names}")
        if not links:
            udp_server.note_unsent(packet_id)
            return
        for index, link in enumerate(links):
            body = meta + payload if index == 0 else payload
            await link.send(Frame(UDP_SEND, 1, index, 0, packet_id if index == 0 else 0, body))

    async def _handshake(self, reader: asyncio.StreamReader, writer: asyncio.StreamWriter, peer) -> tuple[str, int, bool]:
        version, methods_len = (await read_exact(reader, 2))
        if version != SOCKS_VERSION:
            raise ValueError("unsupported socks version")
        await read_exact(reader, methods_len)
        writer.write(b"\x05\x00")
        await writer.drain()
        version, command, _, atyp = await read_exact(reader, 4)
        if version != SOCKS_VERSION:
            raise ValueError("unsupported socks version")
        if atyp == 1:
            host = socket.inet_ntoa(await read_exact(reader, 4))
        elif atyp == 3:
            size = (await read_exact(reader, 1))[0]
            host = (await read_exact(reader, size)).decode()
        else:
            raise ValueError("unsupported atyp")
        port = struct.unpack("!H", await read_exact(reader, 2))[0]
        peer_text = f"{peer[0]}:{peer[1]}" if isinstance(peer, tuple) and len(peer) >= 2 else str(peer)
        if command == 1:
            print(f"[edge] socks handshake peer={peer_text} command=connect target={host}:{port}")
            writer.write(b"\x05\x00\x00\x01\x00\x00\x00\x00\x00\x00")
            await writer.drain()
            return host, port, False
        if command == 3 and self.udp_server and self.udp_server.transport:
            bind_host, bind_port = self.udp_server.transport.get_extra_info("sockname")[:2]
            print(f"[edge] socks handshake peer={peer_text} command=udp_associate target={host}:{port} bind={bind_host}:{bind_port}")
            writer.write(b"\x05\x00\x00\x01" + socket.inet_aton(bind_host) + struct.pack("!H", bind_port))
            await writer.drain()
            return host, port, True
        raise ValueError("unsupported socks command")