"""
Terminal Manager
================

Manages PTY terminal sessions per project with cross-platform support.
Uses winpty (ConPTY) on Windows and built-in pty module on Unix.
"""

import asyncio
import logging
import os
import platform
import shutil
import threading
from pathlib import Path
from typing import Callable, Set

logger = logging.getLogger(__name__)

# Platform detection
IS_WINDOWS = platform.system() == "Windows"

# Conditional imports for PTY support
# Note: Type checking is disabled for cross-platform PTY modules since mypy
# cannot properly handle conditional imports for platform-specific APIs.
if IS_WINDOWS:
    try:
        from winpty import PtyProcess as WinPtyProcess

        WINPTY_AVAILABLE = True
    except ImportError:
        WinPtyProcess = None
        WINPTY_AVAILABLE = False
        logger.warning(
            "winpty package not installed. Terminal sessions will not be available on Windows. "
            "Install with: pip install pywinpty"
        )
else:
    # Unix systems use built-in pty module
    import fcntl
    import pty
    import select
    import signal
    import struct
    import termios

    WINPTY_AVAILABLE = False  # Not applicable on Unix


def _get_shell() -> str:
    """
    Get the appropriate shell for the current platform.

    Returns:
        Path to shell executable
    """
    if IS_WINDOWS:
        # Prefer PowerShell, fall back to cmd.exe
        powershell = shutil.which("powershell.exe")
        if powershell:
            return powershell
        cmd = shutil.which("cmd.exe")
        if cmd:
            return cmd
        # Last resort fallback
        return "cmd.exe"
    else:
        # Unix: Use $SHELL environment variable or fall back to /bin/bash
        shell = os.environ.get("SHELL")
        if shell and shutil.which(shell):
            return shell
        # Fall back to common shells
        for fallback in ["/bin/bash", "/bin/sh"]:
            if os.path.exists(fallback):
                return fallback
        return "/bin/sh"


class TerminalSession:
    """
    Manages a single PTY terminal session for a project.

    Provides cross-platform PTY support with async output streaming
    and multiple output callbacks for WebSocket clients.
    """

    def __init__(self, project_name: str, project_dir: Path):
        """
        Initialize the terminal session.

        Args:
            project_name: Name of the project
            project_dir: Absolute path to the project directory (used as cwd)
        """
        self.project_name = project_name
        self.project_dir = project_dir

        # PTY process references (platform-specific)
        self._pty_process: "WinPtyProcess | None" = None  # Windows winpty
        self._master_fd: int | None = None  # Unix master file descriptor
        self._child_pid: int | None = None  # Unix child process PID

        # State tracking
        self._is_active = False
        self._output_task: asyncio.Task | None = None

        # Output callbacks with thread-safe access
        self._output_callbacks: Set[Callable[[bytes], None]] = set()
        self._callbacks_lock = threading.Lock()

    @property
    def is_active(self) -> bool:
        """Check if the terminal session is currently active."""
        return self._is_active

    @property
    def pid(self) -> int | None:
        """Get the PID of the PTY child process."""
        if IS_WINDOWS:
            if self._pty_process is not None:
                try:
                    pid = self._pty_process.pid
                    return int(pid) if pid is not None else None
                except Exception:
                    return None
            return None
        else:
            return self._child_pid

    def add_output_callback(self, callback: Callable[[bytes], None]) -> None:
        """
        Add a callback to receive terminal output.

        Args:
            callback: Function that receives raw bytes from the PTY
        """
        with self._callbacks_lock:
            self._output_callbacks.add(callback)

    def remove_output_callback(self, callback: Callable[[bytes], None]) -> None:
        """
        Remove an output callback.

        Args:
            callback: The callback to remove
        """
        with self._callbacks_lock:
            self._output_callbacks.discard(callback)

    def _broadcast_output(self, data: bytes) -> None:
        """Broadcast output data to all registered callbacks."""
        with self._callbacks_lock:
            callbacks = list(self._output_callbacks)

        for callback in callbacks:
            try:
                callback(data)
            except Exception as e:
                logger.warning(f"Output callback error: {e}")

    async def start(self, cols: int = 80, rows: int = 24) -> bool:
        """
        Start the PTY terminal session.

        Args:
            cols: Terminal width in columns
            rows: Terminal height in rows

        Returns:
            True if started successfully, False otherwise
        """
        if self._is_active:
            logger.warning(f"Terminal session already active for {self.project_name}")
            return False

        # Validate project directory
        if not self.project_dir.exists():
            logger.error(f"Project directory does not exist: {self.project_dir}")
            return False
        if not self.project_dir.is_dir():
            logger.error(f"Project path is not a directory: {self.project_dir}")
            return False

        shell = _get_shell()
        cwd = str(self.project_dir.resolve())

        try:
            if IS_WINDOWS:
                return await self._start_windows(shell, cwd, cols, rows)
            else:
                return await self._start_unix(shell, cwd, cols, rows)
        except Exception as e:
            logger.exception(f"Failed to start terminal for {self.project_name}: {e}")
            return False

    async def _start_windows(self, shell: str, cwd: str, cols: int, rows: int) -> bool:
        """Start PTY on Windows using winpty."""
        if not WINPTY_AVAILABLE:
            logger.error("Cannot start terminal: winpty package not available")
            # This error will be caught and sent to the client
            raise RuntimeError(
                "Terminal requires pywinpty on Windows. Install with: pip install pywinpty"
            )

        try:
            # WinPtyProcess.spawn expects the shell command
            self._pty_process = WinPtyProcess.spawn(
                shell,
                cwd=cwd,
                dimensions=(rows, cols),
            )
            self._is_active = True

            # Start output reading task
            self._output_task = asyncio.create_task(self._read_output_windows())

            logger.info(f"Terminal started for {self.project_name} (PID: {self.pid}, shell: {shell})")
            return True

        except Exception as e:
            logger.exception(f"Failed to start Windows PTY: {e}")
            self._pty_process = None
            return False

    async def _start_unix(self, shell: str, cwd: str, cols: int, rows: int) -> bool:
        """Start PTY on Unix using built-in pty module."""
        # Note: This entire method uses Unix-specific APIs that don't exist on Windows.
        # Type checking is disabled for these platform-specific calls.
        try:
            # Fork a new pseudo-terminal
            pid, master_fd = pty.fork()  # type: ignore[attr-defined]

            if pid == 0:
                # Child process - exec the shell
                os.chdir(cwd)
                # Set terminal size (Unix-specific modules imported at top-level)
                winsize = struct.pack("HHHH", rows, cols, 0, 0)
                fcntl.ioctl(0, termios.TIOCSWINSZ, winsize)  # type: ignore[attr-defined]

                # Execute the shell
                os.execvp(shell, [shell])
                os._exit(1)  # Fallback if execvp returns (shouldn't happen)
            else:
                # Parent process
                self._master_fd = master_fd
                self._child_pid = pid
                self._is_active = True

                # Set terminal size on master (Unix-specific modules imported at top-level)
                winsize = struct.pack("HHHH", rows, cols, 0, 0)
                fcntl.ioctl(master_fd, termios.TIOCSWINSZ, winsize)  # type: ignore[attr-defined]

                # Start output reading task
                self._output_task = asyncio.create_task(self._read_output_unix())

                logger.info(f"Terminal started for {self.project_name} (PID: {pid}, shell: {shell})")
                return True

        except Exception as e:
            logger.exception(f"Failed to start Unix PTY: {e}")
            self._master_fd = None
            self._child_pid = None
            return False

    async def _read_output_windows(self) -> None:
        """Read output from Windows PTY and broadcast to callbacks."""
        pty = self._pty_process
        if pty is None:
            return

        loop = asyncio.get_running_loop()

        def read_data():
            """Read data from PTY, capturing pty reference to avoid race condition."""
            try:
                if pty.isalive():
                    return pty.read(4096)
            except Exception:
                pass
            return b""

        try:
            while self._is_active and self._pty_process is not None:
                try:
                    # Use run_in_executor for non-blocking read
                    # winpty read() is blocking, so we need to run it in executor
                    data = await loop.run_in_executor(None, read_data)

                    if data:
                        # winpty may return string, convert to bytes if needed
                        if isinstance(data, str):
                            data = data.encode("utf-8", errors="replace")
                        self._broadcast_output(data)
                    else:
                        # Check if process is still alive
                        if self._pty_process is None or not self._pty_process.isalive():
                            break
                        # Small delay to prevent busy loop
                        await asyncio.sleep(0.01)

                except asyncio.CancelledError:
                    raise
                except Exception as e:
                    if self._is_active:
                        logger.warning(f"Windows PTY read error: {e}")
                    break

        except asyncio.CancelledError:
            pass
        finally:
            if self._is_active:
                self._is_active = False
                logger.info(f"Terminal output stream ended for {self.project_name}")

    async def _read_output_unix(self) -> None:
        """Read output from Unix PTY and broadcast to callbacks."""
        if self._master_fd is None:
            return

        loop = asyncio.get_running_loop()

        try:
            while self._is_active and self._master_fd is not None:
                try:
                    # Use run_in_executor with select for non-blocking read
                    def read_with_select():
                        if self._master_fd is None:
                            return b""
                        try:
                            # Wait up to 100ms for data
                            readable, _, _ = select.select([self._master_fd], [], [], 0.1)
                            if readable:
                                return os.read(self._master_fd, 4096)
                            return b""
                        except (OSError, ValueError):
                            return b""

                    data = await loop.run_in_executor(None, read_with_select)

                    if data:
                        self._broadcast_output(data)
                    elif not self._check_child_alive():
                        break

                except asyncio.CancelledError:
                    raise
                except Exception as e:
                    if self._is_active:
                        logger.warning(f"Unix PTY read error: {e}")
                    break

        except asyncio.CancelledError:
            pass
        finally:
            if self._is_active:
                self._is_active = False
                logger.info(f"Terminal output stream ended for {self.project_name}")
            # Reap zombie if not already reaped
            if self._child_pid is not None:
                try:
                    os.waitpid(self._child_pid, os.WNOHANG)
                except ChildProcessError:
                    pass
                except Exception:
                    pass

    def _check_child_alive(self) -> bool:
        """Check if the Unix child process is still alive."""
        if self._child_pid is None:
            return False
        try:
            # Use signal 0 to check if process exists without reaping it.
            # This avoids race conditions with os.waitpid which can reap the process.
            os.kill(self._child_pid, 0)
            return True
        except OSError:
            return False

    def write(self, data: bytes) -> None:
        """
        Write input data to the PTY.

        Args:
            data: Raw bytes to write to the terminal
        """
        if not self._is_active:
            logger.warning(f"Cannot write to inactive terminal for {self.project_name}")
            return

        try:
            if IS_WINDOWS:
                if self._pty_process is not None:
                    # winpty expects string input
                    text = data.decode("utf-8", errors="replace")
                    self._pty_process.write(text)
            else:
                if self._master_fd is not None:
                    os.write(self._master_fd, data)
        except Exception as e:
            logger.warning(f"Failed to write to PTY: {e}")

    def resize(self, cols: int, rows: int) -> None:
        """
        Resize the terminal.

        Args:
            cols: New terminal width in columns
            rows: New terminal height in rows
        """
        if not self._is_active:
            return

        try:
            if IS_WINDOWS:
                if self._pty_process is not None:
                    self._pty_process.setwinsize(rows, cols)
            else:
                if self._master_fd is not None:
                    # Unix-specific modules imported at top-level
                    winsize = struct.pack("HHHH", rows, cols, 0, 0)
                    fcntl.ioctl(self._master_fd, termios.TIOCSWINSZ, winsize)  # type: ignore[attr-defined]

            logger.debug(f"Terminal resized for {self.project_name}: {cols}x{rows}")
        except Exception as e:
            logger.warning(f"Failed to resize terminal: {e}")

    async def stop(self) -> None:
        """Stop the terminal session and clean up resources."""
        if not self._is_active:
            return

        self._is_active = False

        # Cancel output reading task
        if self._output_task is not None:
            self._output_task.cancel()
            try:
                await self._output_task
            except asyncio.CancelledError:
                pass
            self._output_task = None

        try:
            if IS_WINDOWS:
                await self._stop_windows()
            else:
                await self._stop_unix()
        except Exception as e:
            logger.warning(f"Error stopping terminal: {e}")

        logger.info(f"Terminal stopped for {self.project_name}")

    async def _stop_windows(self) -> None:
        """Stop Windows PTY process."""
        if self._pty_process is None:
            return

        try:
            if self._pty_process.isalive():
                self._pty_process.terminate()
                # Give it a moment to terminate
                await asyncio.sleep(0.1)
                if self._pty_process.isalive():
                    self._pty_process.kill()
        except Exception as e:
            logger.warning(f"Error terminating Windows PTY: {e}")
        finally:
            self._pty_process = None

    async def _stop_unix(self) -> None:
        """Stop Unix PTY process."""
        # Note: This method uses Unix-specific signal handling (signal imported at top-level)

        # Close master file descriptor
        if self._master_fd is not None:
            try:
                os.close(self._master_fd)
            except OSError:
                pass
            self._master_fd = None

        # Terminate child process
        if self._child_pid is not None:
            try:
                os.kill(self._child_pid, signal.SIGTERM)
                # Wait briefly for graceful shutdown
                await asyncio.sleep(0.1)
                # Check if still running and force kill if needed
                try:
                    os.kill(self._child_pid, 0)  # Check if process exists
                    # SIGKILL is Unix-specific (Windows would use SIGTERM)
                    os.kill(self._child_pid, signal.SIGKILL)  # type: ignore[attr-defined]
                except ProcessLookupError:
                    pass  # Already terminated
                # Reap the child process to prevent zombie
                try:
                    os.waitpid(self._child_pid, 0)
                except ChildProcessError:
                    pass
            except ProcessLookupError:
                pass  # Already terminated
            except Exception as e:
                logger.warning(f"Error terminating Unix PTY child: {e}")
            finally:
                self._child_pid = None


# Global registry of terminal sessions per project with thread safety
_sessions: dict[str, TerminalSession] = {}
_sessions_lock = threading.Lock()


def get_terminal_session(project_name: str, project_dir: Path) -> TerminalSession:
    """
    Get or create a terminal session for a project (thread-safe).

    Args:
        project_name: Name of the project
        project_dir: Absolute path to the project directory

    Returns:
        TerminalSession instance for the project
    """
    with _sessions_lock:
        if project_name not in _sessions:
            _sessions[project_name] = TerminalSession(project_name, project_dir)
        return _sessions[project_name]


def remove_terminal_session(project_name: str) -> TerminalSession | None:
    """
    Remove a terminal session from the registry.

    Args:
        project_name: Name of the project

    Returns:
        The removed session, or None if not found
    """
    with _sessions_lock:
        return _sessions.pop(project_name, None)


async def cleanup_all_terminals() -> None:
    """
    Stop all active terminal sessions.

    Called on server shutdown to ensure all PTY processes are terminated.
    """
    with _sessions_lock:
        sessions = list(_sessions.values())

    for session in sessions:
        try:
            if session.is_active:
                await session.stop()
        except Exception as e:
            logger.warning(f"Error stopping terminal for {session.project_name}: {e}")

    with _sessions_lock:
        _sessions.clear()

    logger.info("All terminal sessions cleaned up")