from typing import Optional
from fastapi import Depends, HTTPException, Request
from sqlalchemy.orm import Session

from app.core.config import settings
from app.core.database import get_db
from app.core.security import decode_token
from app.models.models import User, UserRole


def _get_auth_token(request: Request) -> Optional[str]:
    return request.cookies.get(settings.AUTH_COOKIE_NAME)


def _get_user_id_from_payload(payload: dict) -> int:
    user_id = payload.get("sub")
    if user_id is None:
        raise HTTPException(status_code=401, detail="Invalid token")

    try:
        return int(user_id)
    except (ValueError, TypeError) as exc:
        raise HTTPException(status_code=401, detail="Invalid token") from exc


def _get_authenticated_user(db: Session, user_id: int, session_id: Optional[str]) -> User:
    user = db.query(User).filter(User.id == user_id, User.is_active.is_(True)).first()
    if not user:
        raise HTTPException(status_code=401, detail="User not found")

    # Single session check — token must match the currently stored session.
    if not session_id or user.current_session_id != session_id:
        raise HTTPException(
            status_code=401,
            detail="Session expired. You logged in from another device.",
        )

    return user


def get_current_user(request: Request, db: Session = Depends(get_db)) -> User:
    token = _get_auth_token(request)
    if not token:
        raise HTTPException(status_code=401, detail="Not authenticated")

    payload = decode_token(token)
    if not payload:
        raise HTTPException(status_code=401, detail="Invalid or expired token")
    if payload.get("auth") != "cookie":
        raise HTTPException(status_code=401, detail="Invalid token")

    user_id = _get_user_id_from_payload(payload)
    session_id = payload.get("sid")
    return _get_authenticated_user(db, user_id, session_id)


def get_optional_current_user(request: Request, db: Session = Depends(get_db)) -> Optional[User]:
    token = request.cookies.get(settings.AUTH_COOKIE_NAME)
    if not token:
        return None
    try:
        user = get_current_user(request, db)
        return user
    except HTTPException:
        return None


def require_admin(current_user: User = Depends(get_current_user)) -> User:
    if current_user.role != UserRole.admin:
        raise HTTPException(status_code=403, detail="Admin access required")
    return current_user


def require_aspirant(current_user: User = Depends(get_current_user)) -> User:
    if current_user.role not in (UserRole.admin, UserRole.aspirant):
        raise HTTPException(
            status_code=403, detail="Access restricted to approved aspirants"
        )
    return current_user