from fastapi import Depends, HTTPException, status
from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
from sqlalchemy import select
from sqlalchemy.orm import selectinload
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.auth import decode_access_token
from app.db.database import get_db
from app.db.models import ClassMembership, User

security = HTTPBearer()

CLASS_PERMISSIONS = {
    "member_view",
    "member_manage",
    "committee_manage",
    "announcement_manage",
    "timeline_manage",
    "vote_manage",
    "schedule_manage",
    "resource_manage",
    "reading_corner_manage",
    "assignment_manage",
    "fund_manage",
    "module_manage",
}

TEACHER_DEFAULT_PERMISSIONS = {
    "member_view",
    "member_manage",
    "committee_manage",
    "announcement_manage",
    "timeline_manage",
    "vote_manage",
    "schedule_manage",
    "resource_manage",
    "reading_corner_manage",
    "assignment_manage",
    "module_manage",
}


async def get_current_user(
    credentials: HTTPAuthorizationCredentials = Depends(security),
    db: AsyncSession = Depends(get_db),
) -> User:
    payload = decode_access_token(credentials.credentials)
    if payload is None:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Token invalid or expired",
        )

    user_id = payload.get("sub")
    if user_id is None:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid token format",
        )

    result = await db.execute(
        select(User)
        .options(
            selectinload(User.memberships),
            selectinload(User.memberships).selectinload(ClassMembership.class_),
        )
        .where(User.id == int(user_id))
    )
    user = result.scalar_one_or_none()

    if user is None:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED, detail="User not found"
        )
    if user.status == "inactive":
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN, detail="Account inactive"
        )
    if user.status == "disabled":
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN, detail="Account disabled"
        )

    return user


def require_role(*roles: str):
    """Factory: returns a dependency that checks user role."""

    async def _check(user: User = Depends(get_current_user)) -> User:
        if user.role not in roles:
            raise HTTPException(
                status_code=status.HTTP_403_FORBIDDEN,
                detail="Insufficient permissions",
            )
        return user

    return _check


def get_membership_for_class(user: User, class_id: int | None) -> ClassMembership | None:
    return user.get_membership(class_id)


def get_active_membership(
    user: User, class_id: int | None = None
) -> ClassMembership | None:
    membership = get_membership_for_class(user, class_id)
    if membership is not None:
        return membership
    return user.get_default_membership()


def get_effective_class_permissions(user: User, class_id: int | None = None) -> set[str]:
    if user.role == "super_admin":
        return set(CLASS_PERMISSIONS)
    membership = get_active_membership(user, class_id)
    scoped_permissions = membership.get_class_permissions() if membership else []
    if user.role == "teacher":
        return set(TEACHER_DEFAULT_PERMISSIONS) | set(scoped_permissions)
    scoped_permissions = [
        permission
        for permission in scoped_permissions
        if permission not in {"member_view", "member_manage", "committee_manage"}
    ]
    return set(scoped_permissions)


def can_access_class(user: User, class_id: int | None) -> bool:
    if class_id is None:
        return False
    if user.role in {"super_admin", "teacher"}:
        return True
    return get_membership_for_class(user, class_id) is not None


def resolve_class_id_for_user(user: User, requested_class_id: int | None) -> int | None:
    if user.role in {"super_admin", "teacher"}:
        return requested_class_id
    if requested_class_id is not None and can_access_class(user, requested_class_id):
        return requested_class_id
    membership = user.get_default_membership()
    return membership.class_id if membership else None


def ensure_class_access(user: User, class_id: int | None):
    if not can_access_class(user, class_id):
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Access denied for this class",
        )


def ensure_class_permission(user: User, permission: str, class_id: int | None = None):
    if permission not in CLASS_PERMISSIONS:
        raise HTTPException(
            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
            detail=f"Unknown permission: {permission}",
        )
    if class_id is not None:
        ensure_class_access(user, class_id)
    if user.role == "super_admin":
        return
    if permission not in get_effective_class_permissions(user, class_id):
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Insufficient permissions",
        )