"""QUIC transport using aioquic for the v2 wire format.

Opens a QUIC connection to the qpq server and provides ``rpc()`` to send
protobuf-encoded requests over individual QUIC streams, reading back the
framed response on the same stream.

aioquic is imported lazily so that the module can be loaded even when
aioquic is not installed (e.g. for tests that only exercise wire/proto).
"""

from __future__ import annotations

import asyncio
import ssl
from typing import Any

from quicprochat.types import ConnectionError, TimeoutError
from quicprochat.wire import HEADER_SIZE, encode_frame, decode_header


def _make_protocol_class() -> type:
    """Build the protocol class at call time so aioquic is imported lazily."""
    from aioquic.asyncio.protocol import QuicConnectionProtocol
    from aioquic.quic.events import StreamDataReceived, QuicEvent

    class _QpqQuicProtocol(QuicConnectionProtocol):
        """QUIC protocol handler that dispatches stream data to waiting futures."""

        def __init__(self, *args: Any, **kwargs: Any) -> None:
            super().__init__(*args, **kwargs)
            self._stream_buffers: dict[int, bytearray] = {}
            self._stream_waiters: dict[int, asyncio.Future[bytes]] = {}

        def quic_event_received(self, event: QuicEvent) -> None:
            if isinstance(event, StreamDataReceived):
                sid = event.stream_id
                buf = self._stream_buffers.setdefault(sid, bytearray())
                buf.extend(event.data)

                if len(buf) >= HEADER_SIZE:
                    _, _, payload_len = decode_header(bytes(buf[:HEADER_SIZE]))
                    total = HEADER_SIZE + payload_len
                    if len(buf) >= total:
                        frame = bytes(buf[:total])
                        del buf[:total]
                        waiter = self._stream_waiters.pop(sid, None)
                        if waiter and not waiter.done():
                            waiter.set_result(frame)

        def wait_for_stream(self, stream_id: int) -> asyncio.Future[bytes]:
            loop = asyncio.get_event_loop()
            fut: asyncio.Future[bytes] = loop.create_future()
            self._stream_waiters[stream_id] = fut

            buf = self._stream_buffers.get(stream_id, bytearray())
            if len(buf) >= HEADER_SIZE:
                _, _, payload_len = decode_header(bytes(buf[:HEADER_SIZE]))
                total = HEADER_SIZE + payload_len
                if len(buf) >= total:
                    frame = bytes(buf[:total])
                    del buf[:total]
                    if not fut.done():
                        fut.set_result(frame)

            return fut

    return _QpqQuicProtocol


class QuicTransport:
    """Async QUIC transport for the qpq v2 wire format.

    Usage::

        transport = await QuicTransport.connect("127.0.0.1:5001")
        response_bytes = await transport.rpc(method_id, request_payload)
        transport.close()
    """

    def __init__(
        self,
        protocol: Any,
        connection: Any,
        request_timeout_ms: int,
    ) -> None:
        self._protocol = protocol
        self._connection = connection
        self._req_id = 0
        self._request_timeout = request_timeout_ms / 1000.0
        self._closed = False

    @staticmethod
    async def connect(
        addr: str,
        *,
        ca_cert_path: str = "",
        server_name: str = "",
        insecure_skip_verify: bool = False,
        connect_timeout_ms: int = 5_000,
        request_timeout_ms: int = 10_000,
    ) -> "QuicTransport":
        """Open a QUIC connection to the server."""
        from aioquic.asyncio import connect as quic_connect
        from aioquic.quic.configuration import QuicConfiguration

        host, _, port_str = addr.rpartition(":")
        if not host:
            host = addr
            port_str = "5001"
        port = int(port_str)

        configuration = QuicConfiguration(
            is_client=True,
            alpn_protocols=["qpq"],
        )

        if insecure_skip_verify:
            configuration.verify_mode = ssl.CERT_NONE
        elif ca_cert_path:
            configuration.load_verify_locations(ca_cert_path)

        if not server_name:
            server_name = host

        proto_cls = _make_protocol_class()

        try:
            async with asyncio.timeout(connect_timeout_ms / 1000.0):
                connection = await quic_connect(
                    host,
                    port,
                    configuration=configuration,
                    create_protocol=proto_cls,
                    server_name=server_name,
                )
        except (OSError, asyncio.TimeoutError) as exc:
            raise ConnectionError(f"failed to connect to {addr}: {exc}") from exc

        protocol = connection._protocol  # type: ignore[attr-defined]
        return QuicTransport(protocol, connection, request_timeout_ms)

    async def rpc(self, method_id: int, payload: bytes) -> bytes:
        """Send an RPC request and return the response payload (protobuf bytes).

        Opens a new QUIC stream for each request.
        """
        if self._closed:
            raise ConnectionError("transport is closed")

        self._req_id += 1
        req_id = self._req_id

        frame = encode_frame(method_id, req_id, payload)

        stream_id = self._protocol._quic.get_next_available_stream_id()
        waiter = self._protocol.wait_for_stream(stream_id)

        self._protocol._quic.send_stream_data(stream_id, frame, end_stream=True)
        self._protocol.transmit()

        try:
            async with asyncio.timeout(self._request_timeout):
                response_frame = await waiter
        except asyncio.TimeoutError as exc:
            raise TimeoutError(
                f"RPC timeout for method {method_id} (req_id={req_id})"
            ) from exc

        _, _, resp_len = decode_header(response_frame)
        return response_frame[HEADER_SIZE : HEADER_SIZE + resp_len]

    @property
    def closed(self) -> bool:
        return self._closed

    def close(self) -> None:
        """Close the QUIC connection."""
        if not self._closed:
            self._closed = True
            self._protocol._quic.close()
            self._protocol.transmit()