"""Atlus — Persistent desktop session manager.

Each user gets one desktop session that survives browser refreshes/closes.
PTY processes are owned by the SessionManager, not by WebSocket connections.
"""

import asyncio
import json
import logging
import os
import pwd
import signal
import time
import uuid
from collections import deque
from dataclasses import dataclass, field
from pathlib import Path
from typing import Optional

from ptyprocess import PtyProcess

from backend.config import DATA_DIR

log = logging.getLogger("atlus.sessions")

SESSIONS_DIR = DATA_DIR / "sessions"
SCROLLBACK_MAXLEN = 5000  # lines of scrollback per terminal


# ---------------------------------------------------------------------------
# Terminal — a long-lived PTY with background reader
# ---------------------------------------------------------------------------

@dataclass
class ManagedTerminal:
    """A PTY process that lives independently of any WebSocket."""

    terminal_id: str
    pty: PtyProcess
    scrollback: deque = field(default_factory=lambda: deque(maxlen=SCROLLBACK_MAXLEN))
    title: str = "Shell"
    created_at: float = field(default_factory=time.time)
    _reader_task: Optional[asyncio.Task] = field(default=None, repr=False)
    _websockets: list = field(default_factory=list, repr=False)

    @property
    def alive(self) -> bool:
        try:
            return self.pty.isalive()
        except Exception:
            return False

    def attach_ws(self, ws):
        """Register a WebSocket to receive live output."""
        if ws not in self._websockets:
            self._websockets.append(ws)

    def detach_ws(self, ws):
        """Unregister a WebSocket."""
        try:
            self._websockets.remove(ws)
        except ValueError:
            pass

    async def _read_loop(self):
        """Background task: read PTY output → scrollback + attached WebSockets."""
        loop = asyncio.get_event_loop()
        while self.alive:
            try:
                raw = await loop.run_in_executor(None, lambda: self.pty.read(4096))
                if not raw:
                    continue
                text = raw.decode("utf-8", errors="replace") if isinstance(raw, bytes) else raw
                self.scrollback.append(text)

                # Fan out to attached WebSockets
                dead = []
                for ws in self._websockets:
                    try:
                        await ws.send_json({"type": "output", "data": text})
                    except Exception:
                        dead.append(ws)
                for ws in dead:
                    self.detach_ws(ws)

            except EOFError:
                break
            except Exception:
                break

        # PTY died — notify attached clients
        for ws in list(self._websockets):
            try:
                await ws.send_json({"type": "output", "data": "\r\n\x1b[31m[Process exited]\x1b[0m\r\n"})
            except Exception:
                pass
        log.info("Terminal %s reader loop ended (pid %s)", self.terminal_id, self.pty.pid)

    def start_reader(self):
        """Start the background reader task."""
        if self._reader_task is None or self._reader_task.done():
            self._reader_task = asyncio.create_task(self._read_loop())

    def kill(self):
        """Terminate the PTY process."""
        if self._reader_task and not self._reader_task.done():
            self._reader_task.cancel()
        if self.alive:
            try:
                self.pty.kill(signal.SIGHUP)
                self.pty.wait()
            except Exception:
                pass

    def to_dict(self) -> dict:
        return {
            "terminal_id": self.terminal_id,
            "title": self.title,
            "alive": self.alive,
            "pid": self.pty.pid,
            "created_at": self.created_at,
        }


# ---------------------------------------------------------------------------
# Desktop Session — one per user
# ---------------------------------------------------------------------------

@dataclass
class DesktopSession:
    """Persistent desktop session for a single user."""

    username: str
    terminals: dict[str, ManagedTerminal] = field(default_factory=dict)
    desktop_state: dict = field(default_factory=dict)  # open apps, active app, etc.
    created_at: float = field(default_factory=time.time)
    last_active: float = field(default_factory=time.time)

    def touch(self):
        self.last_active = time.time()

    def to_dict(self) -> dict:
        return {
            "username": self.username,
            "terminals": {tid: t.to_dict() for tid, t in self.terminals.items() if t.alive},
            "desktop_state": self.desktop_state,
            "created_at": self.created_at,
            "last_active": self.last_active,
        }


# ---------------------------------------------------------------------------
# Session Manager — singleton
# ---------------------------------------------------------------------------

class SessionManager:
    """Manages all user desktop sessions."""

    def __init__(self):
        self._sessions: dict[str, DesktopSession] = {}
        SESSIONS_DIR.mkdir(parents=True, exist_ok=True)

    # ---- Session lifecycle ----

    def get_or_create(self, username: str) -> DesktopSession:
        """Get existing session or create a new one for the user."""
        if username not in self._sessions:
            session = DesktopSession(username=username)
            # Try to restore desktop state from disk
            state_file = SESSIONS_DIR / f"{username}.json"
            if state_file.exists():
                try:
                    data = json.loads(state_file.read_text())
                    session.desktop_state = data.get("desktop_state", {})
                    log.info("Restored desktop state for %s", username)
                except (json.JSONDecodeError, OSError) as e:
                    log.warning("Failed to restore session for %s: %s", username, e)
            self._sessions[username] = session
            log.info("Created session for %s", username)
        session = self._sessions[username]
        session.touch()
        # Prune dead terminals
        self._prune_dead(session)
        return session

    def _prune_dead(self, session: DesktopSession):
        """Remove terminals whose PTY has exited."""
        dead = [tid for tid, t in session.terminals.items() if not t.alive]
        for tid in dead:
            t = session.terminals.pop(tid)
            t.kill()
            log.info("Pruned dead terminal %s for %s", tid, session.username)

    def save_state(self, username: str, desktop_state: dict):
        """Persist desktop state to disk."""
        session = self._sessions.get(username)
        if not session:
            return
        session.desktop_state = desktop_state
        session.touch()

        state_file = SESSIONS_DIR / f"{username}.json"
        try:
            data = {
                "desktop_state": desktop_state,
                "terminal_ids": [
                    {"terminal_id": t.terminal_id, "title": t.title}
                    for t in session.terminals.values() if t.alive
                ],
                "saved_at": time.time(),
            }
            state_file.write_text(json.dumps(data, indent=2))
        except OSError as e:
            log.warning("Failed to save session for %s: %s", username, e)

    # ---- Terminal lifecycle ----

    def create_terminal(self, username: str, cols: int = 120, rows: int = 30) -> ManagedTerminal:
        """Spawn a new PTY terminal for the user."""
        session = self.get_or_create(username)

        # Spawn PTY
        try:
            pw = pwd.getpwnam(username)
        except KeyError:
            pw = None

        shell = pw.pw_shell if pw else "/bin/bash"
        home = pw.pw_dir if pw else "/"

        env = {
            "TERM": "xterm-256color",
            "HOME": home,
            "USER": username,
            "SHELL": shell,
            "LANG": os.environ.get("LANG", "en_US.UTF-8"),
            "PATH": "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
        }

        pty = PtyProcess.spawn(
            [shell, "-l"],
            dimensions=(rows, cols),
            env=env,
            cwd=home,
        )

        terminal_id = str(uuid.uuid4())[:8]
        terminal = ManagedTerminal(
            terminal_id=terminal_id,
            pty=pty,
            title=f"Shell {len(session.terminals) + 1}",
        )
        terminal.start_reader()
        session.terminals[terminal_id] = terminal
        session.touch()

        log.info("Created terminal %s for %s (pid %d)", terminal_id, username, pty.pid)
        return terminal

    def get_terminal(self, username: str, terminal_id: str) -> Optional[ManagedTerminal]:
        """Get a terminal by ID."""
        session = self._sessions.get(username)
        if not session:
            return None
        return session.terminals.get(terminal_id)

    def close_terminal(self, username: str, terminal_id: str) -> bool:
        """Kill and remove a terminal."""
        session = self._sessions.get(username)
        if not session:
            return False
        terminal = session.terminals.pop(terminal_id, None)
        if not terminal:
            return False
        terminal.kill()
        session.touch()
        log.info("Closed terminal %s for %s", terminal_id, username)
        return True

    def list_terminals(self, username: str) -> list[dict]:
        """List all alive terminals for a user."""
        session = self._sessions.get(username)
        if not session:
            return []
        self._prune_dead(session)
        return [t.to_dict() for t in session.terminals.values() if t.alive]

    # ---- Cleanup ----

    async def cleanup_stale(self, max_idle_hours: float = 24):
        """Remove sessions that have been idle too long."""
        cutoff = time.time() - (max_idle_hours * 3600)
        stale = [u for u, s in self._sessions.items() if s.last_active < cutoff]
        for username in stale:
            session = self._sessions.pop(username)
            for terminal in session.terminals.values():
                terminal.kill()
            log.info("Cleaned up stale session for %s (idle since %s)",
                     username, time.ctime(session.last_active))

    def shutdown_all(self):
        """Kill all PTYs — called on server shutdown."""
        for session in self._sessions.values():
            for terminal in session.terminals.values():
                terminal.kill()
        log.info("All sessions shut down")


# ---------------------------------------------------------------------------
# Singleton instance
# ---------------------------------------------------------------------------

manager = SessionManager()