"""
Terminal WebSocket with persistent PTY sessions.

Single Responsibility: only handles PTY lifecycle and WebSocket communication.
Depends on storage.get_zone_path for path resolution (Dependency Inversion).
"""

import asyncio
import collections
import fcntl
import json
import os
import pty
import select
import struct
import termios

from fastapi import APIRouter, WebSocket, WebSocketDisconnect

from config import SCROLLBACK_SIZE
from storage import get_zone_path, check_zone_owner
from auth import get_ws_user

router = APIRouter(tags=["terminal"])

# Active terminals: {zone_name: {fd, pid, buffer, buffer_size, bg_task, ws}}
active_terminals: dict[str, dict] = {}


# ── PTY Management ────────────────────────────

def _spawn_shell(zone_name: str) -> dict:
    """Spawn a new PTY shell for a zone."""
    zone_path = get_zone_path(zone_name)
    master_fd, slave_fd = pty.openpty()

    child_pid = os.fork()
    if child_pid == 0:
        os.setsid()
        os.dup2(slave_fd, 0)
        os.dup2(slave_fd, 1)
        os.dup2(slave_fd, 2)
        os.close(master_fd)
        os.close(slave_fd)
        os.chdir(str(zone_path))
        env = os.environ.copy()
        env["TERM"] = "xterm-256color"
        env["HOME"] = str(zone_path)
        env["PS1"] = f"[{zone_name}] \\w $ "
        os.execvpe("/bin/bash", ["/bin/bash", "--norc"], env)
    else:
        os.close(slave_fd)
        flag = fcntl.fcntl(master_fd, fcntl.F_GETFL)
        fcntl.fcntl(master_fd, fcntl.F_SETFL, flag | os.O_NONBLOCK)
        return {"fd": master_fd, "pid": child_pid, "buffer": collections.deque(), "buffer_size": 0}


def _resize_terminal(zone_name: str, rows: int, cols: int):
    if zone_name in active_terminals:
        fd = active_terminals[zone_name]["fd"]
        winsize = struct.pack("HHHH", rows, cols, 0, 0)
        fcntl.ioctl(fd, termios.TIOCSWINSZ, winsize)


def _append_buffer(info: dict, data: bytes):
    info["buffer"].append(data)
    info["buffer_size"] += len(data)
    while info["buffer_size"] > SCROLLBACK_SIZE:
        old = info["buffer"].popleft()
        info["buffer_size"] -= len(old)


def _get_buffer(info: dict) -> bytes:
    return b"".join(info["buffer"])


def _is_alive(zone_name: str) -> bool:
    if zone_name not in active_terminals:
        return False
    try:
        pid = active_terminals[zone_name]["pid"]
        return os.waitpid(pid, os.WNOHANG) == (0, 0)
    except ChildProcessError:
        active_terminals.pop(zone_name, None)
        return False


async def _bg_reader(zone_name: str):
    """Background: continuously read PTY output into the ring buffer."""
    info = active_terminals.get(zone_name)
    if not info:
        return
    fd = info["fd"]
    while _is_alive(zone_name):
        await asyncio.sleep(0.02)
        try:
            r, _, _ = select.select([fd], [], [], 0)
            if r:
                data = os.read(fd, 4096)
                if data:
                    _append_buffer(info, data)
                    ws = info.get("ws")
                    if ws:
                        try:
                            await ws.send_bytes(data)
                        except Exception:
                            info["ws"] = None
        except (OSError, BlockingIOError):
            pass
        except Exception:
            break


def kill_terminal(zone_name: str):
    """Kill terminal process for a zone."""
    if zone_name in active_terminals:
        info = active_terminals.pop(zone_name)
        bg = info.get("bg_task")
        if bg:
            bg.cancel()
        try:
            os.kill(info["pid"], 9)
            os.waitpid(info["pid"], os.WNOHANG)
        except (ProcessLookupError, ChildProcessError):
            pass
        try:
            os.close(info["fd"])
        except OSError:
            pass


# ── WebSocket Handler ─────────────────────────

@router.websocket("/ws/terminal/{zone_name}")
async def terminal_ws(websocket: WebSocket, zone_name: str):
    # Authenticate via query parameter
    user = get_ws_user(websocket)
    if not user:
        await websocket.close(code=4001, reason="Chưa đăng nhập")
        return

    # Check zone ownership
    try:
        check_zone_owner(zone_name, user.sub, user.role)
    except ValueError as e:
        await websocket.close(code=4003, reason=str(e))
        return

    await websocket.accept()

    try:
        get_zone_path(zone_name)
    except ValueError as e:
        await websocket.send_json({"error": str(e)})
        await websocket.close()
        return

    # Spawn or reuse terminal
    if not _is_alive(zone_name):
        kill_terminal(zone_name)
        try:
            info = _spawn_shell(zone_name)
            info["ws"] = None
            active_terminals[zone_name] = info
            info["bg_task"] = asyncio.create_task(_bg_reader(zone_name))
        except Exception as e:
            await websocket.send_json({"error": f"Cannot create terminal: {e}"})
            await websocket.close()
            return

    info = active_terminals[zone_name]
    fd = info["fd"]

    # Replay buffered scrollback
    buf = _get_buffer(info)
    if buf:
        await websocket.send_bytes(buf)

    # Register this WebSocket as the active receiver
    info["ws"] = websocket

    try:
        while True:
            msg = await websocket.receive()
            if msg.get("type") == "websocket.disconnect":
                break
            if "text" in msg:
                data = json.loads(msg["text"])
                if data.get("type") == "resize":
                    _resize_terminal(zone_name, data.get("rows", 24), data.get("cols", 80))
                elif data.get("type") == "input":
                    os.write(fd, data["data"].encode("utf-8"))
            elif "bytes" in msg:
                os.write(fd, msg["bytes"])
    except WebSocketDisconnect:
        pass
    except Exception:
        pass
    finally:
        if zone_name in active_terminals and active_terminals[zone_name].get("ws") is websocket:
            active_terminals[zone_name]["ws"] = None