"""IPC transport for the Pyra daemon.

Linux/macOS: Unix domain socket at ~/.pyra/daemon.sock (chmod 600, UID-checked).
Windows:     TCP loopback on an OS-assigned port; actual port written to
             ~/.pyra/daemon.port so clients can connect without knowing it ahead
             of time.
"""

from __future__ import annotations

import asyncio
import json
import os
import struct
import sys
from pathlib import Path
from typing import Any, Awaitable, Callable


# ── Protocol types ────────────────────────────────────────────────────────────

IpcMessage = dict[str, Any]   # must have "cmd" key
IpcResponse = dict[str, Any]  # must have "ok" and "data" keys


# ── Encode / decode ───────────────────────────────────────────────────────────

def encode_message(msg: IpcMessage) -> bytes:
    return (json.dumps(msg) + "\n").encode()


def decode_message(line: bytes) -> IpcMessage:
    try:
        return json.loads(line.rstrip(b"\n"))
    except json.JSONDecodeError as exc:
        raise ValueError(f"Invalid IPC message: {exc}") from exc


# ── Address helpers ───────────────────────────────────────────────────────────

def is_unix_socket() -> bool:
    return sys.platform != "win32"


def get_socket_path(cfg_socket_path: str) -> Path:
    """Expand ~ and return the Unix socket path."""
    return Path(cfg_socket_path).expanduser()


def get_port_file_path() -> Path:
    from pyra.utils.paths import pyra_home
    return pyra_home() / "daemon.port"


def _read_windows_port() -> int | None:
    port_file = get_port_file_path()
    try:
        return int(port_file.read_text().strip())
    except (FileNotFoundError, ValueError):
        return None


# ── Server ────────────────────────────────────────────────────────────────────

class IpcServer:
    def __init__(
        self,
        address: Path | tuple[str, int],
        handler: Callable[[IpcMessage], Awaitable[IpcResponse]],
    ) -> None:
        self._address = address
        self._handler = handler
        self._server: asyncio.Server | None = None

    async def start(self) -> None:
        if is_unix_socket():
            assert isinstance(self._address, Path)
            sock_path = self._address
            if sock_path.exists():
                sock_path.unlink()
            self._server = await asyncio.start_unix_server(
                self._handle_client, path=str(sock_path)
            )
            os.chmod(sock_path, 0o600)
        else:
            host, port = self._address if isinstance(self._address, tuple) else ("127.0.0.1", 0)
            self._server = await asyncio.start_server(
                self._handle_client, host=host, port=port
            )
            actual_port = self._server.sockets[0].getsockname()[1]
            port_file = get_port_file_path()
            port_file.write_text(str(actual_port))

        await self._server.start_serving()

    async def stop(self) -> None:
        if self._server is not None:
            self._server.close()
            try:
                await asyncio.wait_for(self._server.wait_closed(), timeout=5.0)
            except asyncio.TimeoutError:
                pass
        if is_unix_socket() and isinstance(self._address, Path):
            try:
                self._address.unlink()
            except FileNotFoundError:
                pass
        else:
            port_file = get_port_file_path()
            try:
                port_file.unlink()
            except FileNotFoundError:
                pass

    async def _handle_client(
        self, reader: asyncio.StreamReader, writer: asyncio.StreamWriter
    ) -> None:
        try:
            if is_unix_socket() and not self._check_peer_uid(writer):
                writer.close()
                return

            line = await asyncio.wait_for(reader.readline(), timeout=5.0)
            if not line:
                return

            try:
                msg = decode_message(line)
            except ValueError:
                resp: IpcResponse = {"ok": False, "data": {"error": "invalid JSON"}}
            else:
                resp = await self._handler(msg)

            writer.write(encode_message(resp))
            await writer.drain()
        except (asyncio.TimeoutError, ConnectionResetError, BrokenPipeError):
            pass
        finally:
            try:
                writer.close()
                await writer.wait_closed()
            except Exception:
                pass

    def _check_peer_uid(self, writer: asyncio.StreamWriter) -> bool:
        """Return True if the peer's UID matches ours. Falls back to True on error."""
        try:
            peer_uid = _get_peer_uid(writer)
            if peer_uid is None:
                return True  # can't determine — allow (socket perms are the guard)
            return peer_uid == os.getuid()
        except Exception:
            return True  # don't crash the server on unexpected errors


# ── Client ────────────────────────────────────────────────────────────────────

class IpcClient:
    def __init__(self, address: Path | tuple[str, int]) -> None:
        self._address = address

    async def send(self, msg: IpcMessage, timeout: float = 5.0) -> IpcResponse:
        if is_unix_socket():
            assert isinstance(self._address, Path)
            reader, writer = await asyncio.wait_for(
                asyncio.open_unix_connection(str(self._address)), timeout=timeout
            )
        else:
            host, port = self._address if isinstance(self._address, tuple) else ("127.0.0.1", 0)
            reader, writer = await asyncio.wait_for(
                asyncio.open_connection(host, port), timeout=timeout
            )

        try:
            writer.write(encode_message(msg))
            await writer.drain()
            line = await asyncio.wait_for(reader.readline(), timeout=timeout)
            return decode_message(line)
        finally:
            writer.close()
            try:
                await writer.wait_closed()
            except Exception:
                pass


def send_command(
    address: Path | tuple[str, int],
    msg: IpcMessage,
    timeout: float = 5.0,
) -> IpcResponse:
    """Synchronous wrapper around IpcClient.send() for CLI callers."""
    return asyncio.run(IpcClient(address).send(msg, timeout=timeout))


# ── Peer UID detection ────────────────────────────────────────────────────────

def _get_peer_uid(writer: asyncio.StreamWriter) -> int | None:
    """Return the connecting peer's UID, or None if unavailable."""
    try:
        sock = writer.get_extra_info("socket")
        if sock is None:
            return None

        if sys.platform == "linux":
            # SO_PEERCRED: struct { pid_t pid; uid_t uid; gid_t gid; }
            SO_PEERCRED = 17
            cred = sock.getsockopt(
                socket_module().SOL_SOCKET, SO_PEERCRED, struct.calcsize("3i")
            )
            _pid, uid, _gid = struct.unpack("3i", cred)
            return uid

        if sys.platform == "darwin":
            return _macos_peer_uid(sock.fileno())

    except Exception:
        pass
    return None


def socket_module():  # lazy import to avoid top-level import on non-Unix
    import socket
    return socket


def _macos_peer_uid(fd: int) -> int | None:
    """Use getpeereid(2) via ctypes to retrieve the peer UID on macOS."""
    import ctypes
    import ctypes.util

    libc_name = ctypes.util.find_library("c")
    if not libc_name:
        return None
    libc = ctypes.CDLL(libc_name)

    euid = ctypes.c_uint32(0)
    egid = ctypes.c_uint32(0)
    if libc.getpeereid(fd, ctypes.byref(euid), ctypes.byref(egid)) != 0:
        return None
    return euid.value