"""Session-based authentication, password hashing, and RBAC."""

from __future__ import annotations

import hashlib
import logging
import secrets
import uuid
from datetime import UTC, datetime, timedelta
from typing import Any

import redis.asyncio as aioredis
from passlib.context import CryptContext
from sqlalchemy.ext.asyncio import AsyncSession

from app.config import get_settings
from app.models.session import Session as SessionModel
from app.models.user import User

logger = logging.getLogger(__name__)

_pwd_context = CryptContext(
    schemes=["bcrypt"], deprecated="auto", bcrypt__rounds=get_settings().bcrypt_rounds
)

# ── Global Redis client singleton ────────────────────────────────────────────
_redis_client: aioredis.Redis | None = None


async def init_redis() -> aioredis.Redis:
    """Create and store the global Redis client. Called once during app lifespan startup."""
    global _redis_client
    if _redis_client is not None:
        logger.warning("init_redis() called but Redis client already initialized")
        return _redis_client
    _redis_client = aioredis.from_url(
        get_settings().redis_url, decode_responses=True
    )
    logger.info("Global Redis client initialized")
    return _redis_client


async def close_redis() -> None:
    """Close the global Redis client. Called during app lifespan shutdown."""
    global _redis_client
    if _redis_client is not None:
        await _redis_client.aclose()
        _redis_client = None
        logger.info("Global Redis client closed")


def get_redis() -> aioredis.Redis:
    """Return the global Redis client singleton.

    If init_redis() has not been called yet (e.g. during testing or
    outside the app lifespan), a new client is created lazily so callers
    always get a working connection.
    """
    global _redis_client
    if _redis_client is None:
        _redis_client = aioredis.from_url(
            get_settings().redis_url, decode_responses=True
        )
        logger.debug("Redis client created lazily (init_redis not called)")
    return _redis_client


def hash_password(password: str) -> str:
    """Hash a password using bcrypt."""
    return _pwd_context.hash(password)


def verify_password(password: str, password_hash: str) -> bool:
    """Verify a password against a bcrypt hash."""
    return _pwd_context.verify(password, password_hash)


def generate_session_token() -> str:
    """Generate a cryptographically secure session token."""
    return secrets.token_urlsafe(32)


def generate_csrf_token() -> str:
    """Generate a CSRF token."""
    return secrets.token_urlsafe(32)


def hash_token(token: str) -> str:
    """SHA-256 hash a token for storage."""
    return hashlib.sha256(token.encode()).hexdigest()


async def verify_ws_origin(websocket) -> bool:
    """Verify that the WebSocket upgrade request comes from an allowed origin.

    Checks the Origin header against the configured CORS origins.
    Also validates a CSRF token query parameter against the session.
    Returns True if the origin is allowed and CSRF token is valid.
    """
    from app.config import get_settings
    settings = get_settings()
    allowed_origins = settings.cors_origin_list
    if not allowed_origins:
        return True
    origin = websocket.headers.get("origin", "")
    if not origin:
        # Non-browser clients (curl, etc.) don't send Origin.
        # Reject when CORS is configured — WebSocket should come from a browser.
        logger.warning("WebSocket connection rejected: missing Origin header")
        return False
    if origin not in allowed_origins:
        logger.warning("WebSocket connection rejected: invalid Origin %s", origin)
        return False

    # CSRF token validation: check query parameter 'csrf_token' against session
    # The frontend must send ?csrf_token=xxx in the WebSocket URL
    # This prevents cross-site WebSocket hijacking attacks
    csrf_token = websocket.query_params.get("csrf_token", "")
    if not csrf_token:
        logger.warning("WebSocket connection rejected: missing csrf_token query parameter")
        return False

    # Validate CSRF token against session in Redis
    session_id = websocket.cookies.get(settings.session_cookie_name)
    if not session_id:
        logger.warning("WebSocket connection rejected: missing session cookie")
        return False

    redis = get_redis()
    session_data = await get_session_data(redis, session_id)
    if not session_data or session_data.get("csrf_token") != csrf_token:
        logger.warning("WebSocket connection rejected: invalid CSRF token")
        return False

    return True


async def create_session(
    db: AsyncSession,
    redis: aioredis.Redis,
    user: User,
    tenant_id: uuid.UUID,
    role: str = "viewer",
) -> tuple[str, str]:
    """Create a session in Redis (runtime) and PostgreSQL (audit trail).
    Returns (session_id, csrf_token).

    ``role`` comes from UserTenant — the built-in role string for the
    active tenant membership.
    """
    settings = get_settings()
    session_id = str(uuid.uuid4())
    csrf_token = generate_csrf_token()
    expires_at = datetime.now(UTC) + timedelta(seconds=settings.session_ttl_seconds)

    # Redis runtime session
    session_data: dict[str, Any] = {
        "user_id": str(user.id),
        "tenant_id": str(tenant_id),
        "email": user.email,
        "name": user.name,
        "role": role,
        "is_system_admin": user.is_system_admin,
        "csrf_token": csrf_token,
        "is_active": user.is_active,
    }
    import json

    await redis.setex(
        f"session:{session_id}",
        settings.session_ttl_seconds,
        json.dumps(session_data),
    )

    # PostgreSQL audit trail
    audit_record = SessionModel(
        id=uuid.UUID(session_id),
        user_id=user.id,
        tenant_id=tenant_id,
        csrf_token=csrf_token,
        expires_at=expires_at,
    )
    db.add(audit_record)
    await db.flush()

    return session_id, csrf_token


async def get_session_data(redis: aioredis.Redis, session_id: str) -> dict[str, Any] | None:
    """Retrieve session data from Redis with DB fallback.

    Tries Redis first. If Redis is unavailable, falls back to PostgreSQL
    sessions table (audit trail) to keep users logged in during Redis outages.
    """
    import json

    from app.core.resilience import get_circuit

    circuit = get_circuit("redis")
    if await circuit.can_proceed():
        try:
            raw = await redis.get(f"session:{session_id}")
            await circuit.record_success()
            if raw is None:
                return None
            return json.loads(raw)
        except Exception as exc:
            logger.warning("Redis session lookup failed: %s — falling back to DB", exc)
            await circuit.record_failure()

    # DB fallback: query sessions table
    try:
        from datetime import UTC, datetime

        from sqlalchemy import select

        from app.core.db import get_auth_session_factory
        from app.models.session import Session as SessionModel

        factory = get_auth_session_factory()
        async with factory() as db:
            result = await db.execute(
                select(SessionModel).where(SessionModel.id == uuid.UUID(session_id))
            )
            session = result.scalar_one_or_none()
            if session is None or session.expires_at < datetime.now(UTC):
                return None
            # Load actual user is_active status from DB instead of hardcoding True
            from app.models.user import User
            user_result = await db.execute(
                select(User.is_active).where(User.id == session.user_id)
            )
            user_active = user_result.scalar()
            if user_active is None or not user_active:
                return None  # User deleted or deactivated
            return {
                "user_id": str(session.user_id),
                "tenant_id": str(session.tenant_id),
                "csrf_token": session.csrf_token,
                "is_active": user_active,
            }
    except Exception as db_exc:
        logger.error("DB fallback for session lookup also failed: %s", db_exc)
        return None


async def refresh_session_ttl(redis: aioredis.Redis, session_id: str) -> None:
    """Extend the Redis session TTL on activity (sliding session)."""
    settings = get_settings()
    await redis.expire(f"session:{session_id}", settings.session_ttl_seconds)


async def invalidate_session(redis: aioredis.Redis, session_id: str) -> None:
    """Delete a session from Redis AND PostgreSQL (logout)."""
    await redis.delete(f"session:{session_id}")
    # Also invalidate in PostgreSQL fallback
    try:
        from sqlalchemy import delete

        from app.core.db import get_session_factory
        from app.models.session import SessionModel
        factory = get_session_factory()
        async with factory() as db:
            await db.execute(
                delete(SessionModel).where(SessionModel.id == uuid.UUID(session_id))
            )
            await db.commit()
    except Exception as e:
        logger.warning("Failed to invalidate PostgreSQL session: %s", e)


async def invalidate_all_user_sessions(redis: aioredis.Redis, user_id: uuid.UUID) -> int:
    """Invalidate ALL sessions for a user (logout all devices).

    Uses SCAN to find all session keys, checks user_id match, deletes.
    Returns number of sessions deleted.
    """
    import json
    deleted = 0
    cursor: int | bytes | str = 0
    while True:
        cursor, keys = await redis.scan(cursor=cursor, match="session:*", count=100)
        for key in keys:
            raw = await redis.get(key)
            if raw:
                try:
                    data = json.loads(raw)
                    if data.get("user_id") == str(user_id):
                        await redis.delete(key)
                        deleted += 1
                except (json.JSONDecodeError, TypeError):
                    pass
        if int(cursor) == 0:
            break
    logger.info("Invalidated %d sessions for user %s", deleted, user_id)
    return deleted


async def update_session_tenant(
    redis: aioredis.Redis,
    session_id: str,
    new_tenant_id: uuid.UUID,
    role: str | None = None,
) -> dict[str, Any] | None:
    """Update the active tenant (and optionally role) in a Redis session."""
    import json

    settings = get_settings()
    raw = await redis.get(f"session:{session_id}")
    if raw is None:
        return None
    data = json.loads(raw)
    data["tenant_id"] = str(new_tenant_id)
    if role is not None:
        data["role"] = role
    ttl = await redis.ttl(f"session:{session_id}")
    if ttl <= 0:
        ttl = settings.session_ttl_seconds
    await redis.setex(f"session:{session_id}", ttl, json.dumps(data))
    return data


# ⚠️ Legacy check_permission and filter_fields_by_permission removed from auth.py.
# Use app.core.permissions.check_permission and app.core.permissions.filter_fields_by_permission instead.
# Tests should import directly from app.core.permissions.