# backend/auth/user_store.py
# CRUD operations on data/users.json with atomic writes.
# File is read on each auth request (no stale cache), written atomically
# via tmp+rename to prevent corruption on crash.

import json
import logging
import shutil
import threading
import uuid
from datetime import datetime, timedelta, timezone
from pathlib import Path

from .password import hash_password

logger = logging.getLogger("obsigate.auth.users")

USERS_FILE = Path("data/users.json")

# Serialises read-modify-write cycles on users.json.  ``RLock`` because a few
# helpers (e.g. ``record_login_failure``) call other mutators while holding it.
# BUG-029: without this, concurrent MFA enable + password change could lose one
# of the two updates (last writer wins).
_users_lock = threading.RLock()


def _read() -> dict:
    """Read users.json. Returns empty structure if file doesn't exist."""
    if not USERS_FILE.exists():
        return {"version": 1, "users": {}}
    try:
        return json.loads(USERS_FILE.read_text(encoding="utf-8"))
    except (json.JSONDecodeError, OSError) as e:
        logger.error(f"Failed to read users.json: {e}")
        return {"version": 1, "users": {}}


def _write(data: dict):
    """Atomic write: write to .tmp then rename to prevent corruption."""
    try:
        USERS_FILE.parent.mkdir(parents=True, exist_ok=True)
        tmp = USERS_FILE.with_suffix(".tmp")
        tmp.write_text(json.dumps(data, indent=2, default=str), encoding="utf-8")
        shutil.move(str(tmp), str(USERS_FILE))
        try:
            USERS_FILE.chmod(0o600)
        except OSError:
            pass  # Windows doesn't support Unix permissions
    except PermissionError as e:
        logger.critical("=" * 60)
        logger.critical(f"ERREUR DE PERMISSION : Impossible d'écrire dans {USERS_FILE.parent}")
        logger.critical("Le conteneur n'a pas les droits sur le volume monté dans /app/data.")
        logger.critical("FIX : Exécutez sur l'hôte (Linux) : sudo chown -R 1000:1000 /votre/chemin/data")
        logger.critical("=" * 60)
        raise e


def has_users() -> bool:
    """Check if any users exist."""
    return bool(_read()["users"])


def get_user(username: str) -> dict | None:
    """Get a user by username. Returns None if not found."""
    return _read()["users"].get(username)


def get_all_users() -> list[dict]:
    """Get all users WITHOUT password_hash (safe for API responses)."""
    users = _read()["users"]
    return [
        {k: v for k, v in u.items() if k != "password_hash"}
        for u in users.values()
    ]


def create_user(
    username: str,
    password: str,
    role: str = "user",
    vaults: list[str] | None = None,
    display_name: str | None = None,
) -> dict:
    """Create a new user. Raises ValueError if username already taken."""
    with _users_lock:
        data = _read()
        if username in data["users"]:
            raise ValueError(f"User '{username}' already exists")

        user = {
            "id": str(uuid.uuid4()),
            "username": username,
            "display_name": display_name or username,
            "password_hash": hash_password(password),
            "role": role,
            "vaults": vaults or [],
            "active": True,
            "language": "fr",  # default UI language
            "avatar": None,  # profile picture data-URL (#113)
            "created_at": datetime.now(timezone.utc).isoformat(),
            "password_changed_at": datetime.now(timezone.utc).timestamp(),
            "last_login": None,
            "failed_attempts": 0,
            "locked_until": None,
        }
        data["users"][username] = user
        _write(data)
    logger.info(f"Created user '{username}' (role={role})")
    return {k: v for k, v in user.items() if k != "password_hash"}


def update_user(username: str, updates: dict) -> dict:
    """Update user fields. Raises ValueError if user not found.

    Forbidden fields (id, username, created_at) are silently ignored.
    If 'password' is in updates, it's hashed and stored as password_hash.
    """
    with _users_lock:
        data = _read()
        if username not in data["users"]:
            raise ValueError(f"User '{username}' not found")

        forbidden = {"id", "username", "created_at"}
        safe_updates = {k: v for k, v in updates.items() if k not in forbidden}

        if "password" in safe_updates:
            safe_updates["password_hash"] = hash_password(safe_updates.pop("password"))
            # BUG-028: invalidate every token issued before this change.
            safe_updates["password_changed_at"] = datetime.now(timezone.utc).timestamp()

        data["users"][username].update(safe_updates)
        _write(data)
        result = {k: v for k, v in data["users"][username].items() if k != "password_hash"}
    return result


def delete_user(username: str):
    """Delete a user. Raises ValueError if not found."""
    with _users_lock:
        data = _read()
        if username not in data["users"]:
            raise ValueError(f"User '{username}' not found")
        del data["users"][username]
        _write(data)
    logger.info(f"Deleted user '{username}'")


def record_login_success(username: str):
    """Record a successful login: update last_login, reset failed attempts."""
    update_user(username, {
        "last_login": datetime.now(timezone.utc).isoformat(),
        "failed_attempts": 0,
        "locked_until": None,
    })


def record_login_failure(username: str) -> int:
    """Record a failed login. Returns the new attempt count.

    After 5 failures, locks the account for 15 minutes.
    """
    with _users_lock:
        data = _read()
        user = data["users"].get(username)
        if not user:
            return 0

        attempts = user.get("failed_attempts", 0) + 1
        updates = {"failed_attempts": attempts}

        # Lock after 5 failed attempts (15 minutes)
        if attempts >= 5:
            locked_until = (
                datetime.now(timezone.utc) + timedelta(minutes=15)
            ).isoformat()
            updates["locked_until"] = locked_until
            logger.warning(f"Account '{username}' locked after {attempts} failed attempts")

        update_user(username, updates)
        return attempts


def is_locked(username: str) -> bool:
    """Check if an account is temporarily locked.

    Auto-unlocks if the lock period has expired.
    """
    user = get_user(username)
    if not user or not user.get("locked_until"):
        return False
    locked_until = datetime.fromisoformat(user["locked_until"])
    if datetime.now(timezone.utc) > locked_until:
        # Lock expired — unlock
        update_user(username, {"locked_until": None, "failed_attempts": 0})
        return False
    return True