"""Collaboration temps réel — édition simultanée (ROADMAP #62).

Ce module implémente le cœur serveur de l'édition collaborative :

* un **relais WebSocket** : une *room* est créée par fichier ouvert
  (clé ``vault::chemin``) et tous les clients qui éditent le même fichier
  rejoignent la même room ;
* un **relais de mises à jour Yjs** (CRDT) : le serveur ne décode pas le
  format binaire Yjs, il stocke le journal des mises à jour reçues et le
  rejoue aux nouveaux arrivants. La fusion sans conflit est assurée côté
  client par Yjs ;
* un **awareness** (curseurs colorés + sélections) relayé entre clients ;
* une **persistance différée** : le texte markdown reçu des clients est écrit
  sur disque après un debounce (2 s par défaut).

Sécurité : chaque connexion est authentifiée manuellement (les dépendances
FastAPI ``Depends`` ne s'exécutent pas pour ``@app.websocket``), puis le
chemin est validé via :func:`backend.services.paths.resolve_safe_path` et
l'accès à la vault via ``check_vault_access``.
"""

from __future__ import annotations

import asyncio
import base64
import json
import logging
import time
from dataclasses import dataclass, field
from pathlib import Path
from typing import Any

from fastapi import WebSocket
from starlette.websockets import WebSocketDisconnect

logger = logging.getLogger("obsigate.collab")

#: Délai (secondes) sans modification avant écriture sur disque.
SAVE_DEBOUNCE_SECONDS = 2.0

#: Taille maximale d'une mise à jour Yjs encodée (protection anti-abus).
MAX_UPDATE_BYTES = 8 * 1024 * 1024

#: Taille maximale d'un snapshot texte (protection anti-abus).
MAX_TEXT_CHARS = 8 * 1024 * 1024

#: Taille maximale d'un message brut reçu (protection anti-abus, BUG-036).
MAX_MESSAGE_CHARS = 16 * 1024 * 1024

#: Palette de couleurs attribuées aux utilisateurs (curseurs + avatars).
PEER_COLORS = [
    "#e6194b", "#3cb44b", "#4363d8", "#f58231", "#911eb4",
    "#008080", "#9a6324", "#800000", "#808000", "#000075",
]


def color_for_index(index: int) -> str:
    """Return a deterministic cursor color for a peer index."""
    return PEER_COLORS[index % len(PEER_COLORS)]


def _b64encode(data: bytes) -> str:
    return base64.b64encode(data).decode("ascii")


def _b64decode(data: str) -> bytes:
    return base64.b64decode(data.encode("ascii"))


def authenticate_websocket(websocket: WebSocket) -> dict[str, Any] | None:
    """Authenticate a WebSocket connection.

    Mirrors :func:`backend.auth.middleware.get_current_user` but works on the
    WebSocket scope: the JWT is read from the ``access_token`` cookie, which
    same-origin browsers send automatically during the handshake.

    BUG-036: the token is **never** accepted from the query string anymore —
    URLs end up in access logs, proxies and browser history. Browsers cannot
    set custom headers on a WebSocket handshake, so the HttpOnly cookie set at
    login is the only supported transport.

    Returns the user dict, or ``None`` if authentication fails.
    """
    from backend.auth.jwt_handler import decode_token
    from backend.auth.middleware import is_auth_enabled
    from backend.auth.user_store import get_user

    if not is_auth_enabled():
        return {
            "username": "anonymous",
            "display_name": "Anonymous",
            "role": "admin",
            "vaults": ["*"],
            "active": True,
            "_token_vaults": ["*"],
        }

    token = websocket.cookies.get("access_token")
    if not token:
        return None

    payload = decode_token(token)
    if not payload or payload.get("type") != "access":
        return None

    user = get_user(payload["sub"])
    if not user or not user.get("active"):
        return None

    user["_token_vaults"] = payload.get("vaults", [])
    user["_token_jti"] = payload.get("jti")
    return user


@dataclass
class CollabClient:
    """A single WebSocket connection inside a collaboration room."""

    conn_id: int
    websocket: WebSocket
    username: str
    display_name: str
    color: str
    y_client_id: int | None = None
    awareness: dict[str, Any] | None = None

    def peer(self) -> dict[str, Any]:
        return {
            "connId": self.conn_id,
            "clientId": self.y_client_id,
            "username": self.username,
            "displayName": self.display_name,
            "color": self.color,
        }


@dataclass
class CollabRoom:
    """State shared by every client editing the same file."""

    vault: str
    path: str
    file_path: Path
    initial_text: str = ""
    clients: dict[int, CollabClient] = field(default_factory=dict)
    #: Journal des mises à jour Yjs (binaires) depuis la création de la room.
    updates: list[bytes] = field(default_factory=list)
    has_updates: bool = False
    seed_sent: bool = False
    pending_text: str | None = None
    save_task: asyncio.Task | None = None
    lock: asyncio.Lock = field(default_factory=asyncio.Lock)

    @property
    def key(self) -> str:
        return f"{self.vault}::{self.path}"

    def peers(self) -> list[dict[str, Any]]:
        return [client.peer() for client in self.clients.values()]

    def awareness_snapshot(self) -> list[dict[str, Any]]:
        return [
            {"clientId": c.y_client_id, "state": c.awareness}
            for c in self.clients.values()
            if c.y_client_id is not None and c.awareness is not None
        ]


class CollabManager:
    """Manages collaboration rooms, broadcasting and disk persistence."""

    def __init__(self, save_debounce: float = SAVE_DEBOUNCE_SECONDS) -> None:
        self._rooms: dict[str, CollabRoom] = {}
        self._save_debounce = save_debounce
        self._next_conn_id = 1
        self._lock = asyncio.Lock()

    # -- introspection (used by tests / diagnostics) ------------------------
    @property
    def room_count(self) -> int:
        return len(self._rooms)

    def room_peer_count(self, vault: str, path: str) -> int:
        room = self._rooms.get(f"{vault}::{path}")
        return len(room.clients) if room else 0

    def get_room(self, vault: str, path: str) -> CollabRoom | None:
        return self._rooms.get(f"{vault}::{path}")

    # -- lifecycle ----------------------------------------------------------
    async def connect(
        self,
        websocket: WebSocket,
        vault: str,
        path: str,
        file_path: Path,
        user: dict[str, Any],
    ) -> None:
        """Register *websocket* in the room and relay messages until it closes."""
        async with self._lock:
            key = f"{vault}::{path}"
            room = self._rooms.get(key)
            if room is None:
                try:
                    initial_text = file_path.read_text(encoding="utf-8")
                except (OSError, UnicodeDecodeError):
                    initial_text = ""
                room = CollabRoom(vault=vault, path=path, file_path=file_path, initial_text=initial_text)
                self._rooms[key] = room

            conn_id = self._next_conn_id
            self._next_conn_id += 1
            client = CollabClient(
                conn_id=conn_id,
                websocket=websocket,
                username=user.get("username", "anonymous"),
                display_name=user.get("display_name") or user.get("username", "anonymous"),
                color=color_for_index(conn_id - 1),
            )
            room.clients[conn_id] = client

            seed: str | None = None
            if not room.has_updates and not room.seed_sent:
                seed = room.initial_text
                room.seed_sent = True

            await websocket.send_json({
                "type": "init",
                "connId": conn_id,
                "color": client.color,
                "seed": seed,
                "updates": [_b64encode(u) for u in room.updates],
                "peers": room.peers(),
                "awareness": room.awareness_snapshot(),
            })
            await self._broadcast(room, {"type": "peer_joined", "peer": client.peer()}, exclude=conn_id)

        try:
            while True:
                raw = await websocket.receive_text()
                await self._on_message(room, client, raw)
        except WebSocketDisconnect:
            pass
        except Exception as exc:  # pragma: no cover - defensive
            logger.debug("Collab connection error (%s): %s", room.key, exc)
        finally:
            await self.disconnect(room, client)

    async def disconnect(self, room: CollabRoom, client: CollabClient) -> None:
        """Remove *client* from *room*, flushing and cleaning up if empty."""
        async with self._lock:
            room.clients.pop(client.conn_id, None)
            empty = not room.clients
        if empty:
            await self._flush(room)
            async with self._lock:
                # Only delete if nobody rejoined while we were flushing.
                if not room.clients and self._rooms.get(room.key) is room:
                    if room.save_task:
                        room.save_task.cancel()
                    self._rooms.pop(room.key, None)
        else:
            await self._broadcast(
                room,
                {
                    "type": "peer_left",
                    "peer": client.peer(),
                    "clientId": client.y_client_id,
                },
            )

    async def stop(self) -> None:
        """Flush and cancel every room (called on application shutdown)."""
        async with self._lock:
            rooms = list(self._rooms.values())
            self._rooms.clear()
        for room in rooms:
            if room.save_task:
                room.save_task.cancel()
            await self._flush(room)

    # -- message handling ---------------------------------------------------
    async def _on_message(self, room: CollabRoom, client: CollabClient, raw: str) -> None:
        # BUG-036: drop oversized frames before parsing them.
        if not isinstance(raw, str) or len(raw) > MAX_MESSAGE_CHARS:
            return
        try:
            message = json.loads(raw)
        except (ValueError, TypeError):
            return
        if not isinstance(message, dict):
            return

        msg_type = message.get("type")

        if msg_type in ("sync", "update"):
            encoded = message.get("update")
            if not isinstance(encoded, str):
                return
            try:
                update = _b64decode(encoded)
            except (ValueError, TypeError):
                return
            if not update or len(update) > MAX_UPDATE_BYTES:
                return
            async with self._lock:
                room.updates.append(update)
                room.has_updates = True
            await self._broadcast(
                room,
                {"type": "update", "update": encoded, "from": client.conn_id},
                exclude=client.conn_id,
            )

        elif msg_type == "awareness":
            y_client_id = message.get("clientId")
            state = message.get("state")
            if not isinstance(y_client_id, int):
                return
            client.y_client_id = y_client_id
            client.awareness = state if isinstance(state, dict) else None
            await self._broadcast(
                room,
                {
                    "type": "awareness",
                    "clientId": y_client_id,
                    "state": client.awareness,
                    "from": client.conn_id,
                },
                exclude=client.conn_id,
            )

        elif msg_type == "text":
            text = message.get("text")
            if not isinstance(text, str) or len(text) > MAX_TEXT_CHARS:
                return
            room.pending_text = text
            self._schedule_save(room)

        elif msg_type == "ping":
            await client.websocket.send_json({"type": "pong", "t": int(time.time() * 1000)})

    # -- broadcasting -------------------------------------------------------
    async def _broadcast(self, room: CollabRoom, message: dict[str, Any], exclude: int | None = None) -> None:
        dead: list[CollabClient] = []
        for client in list(room.clients.values()):
            if exclude is not None and client.conn_id == exclude:
                continue
            try:
                await client.websocket.send_json(message)
            except Exception:
                dead.append(client)
        for client in dead:
            room.clients.pop(client.conn_id, None)

    # -- persistence --------------------------------------------------------
    def _schedule_save(self, room: CollabRoom) -> None:
        if room.save_task and not room.save_task.done():
            room.save_task.cancel()
        try:
            loop = asyncio.get_running_loop()
        except RuntimeError:  # pragma: no cover - no running loop (tests)
            return
        room.save_task = loop.create_task(self._debounced_save(room))

    async def _debounced_save(self, room: CollabRoom) -> None:
        try:
            await asyncio.sleep(self._save_debounce)
        except asyncio.CancelledError:
            return
        await self._flush(room)

    async def _flush(self, room: CollabRoom) -> None:
        """Write the last received text snapshot to disk (if any)."""
        async with room.lock:
            text = room.pending_text
            room.pending_text = None
        if text is None:
            return
        try:
            await asyncio.to_thread(room.file_path.write_text, text, encoding="utf-8")
            logger.debug("Collab persisted %s", room.key)
        except OSError as exc:
            logger.warning("Collab persist failed for %s: %s", room.key, exc)


#: Process-wide singleton used by the WebSocket endpoint.
collab_manager = CollabManager()