from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.orm import Session
from typing import List

from app.core.database import get_db
from app.models.department import Department
from app.models.user import User
from app.schemas.department import DepartmentCreate, DepartmentUpdate, DepartmentResponse
from app.middleware.auth import require_permission, require_system_admin

router = APIRouter()


@router.get("", response_model=List[DepartmentResponse])
async def list_departments(
    skip: int = 0,
    limit: int = 100,
    db: Session = Depends(get_db),
    current_user: User = Depends(require_permission("users.read")),
):
    """
    List all departments.
    """
    departments = db.query(Department).offset(skip).limit(limit).all()
    return departments


@router.get("/{department_id}", response_model=DepartmentResponse)
async def get_department(
    department_id: str,
    db: Session = Depends(get_db),
    current_user: User = Depends(require_permission("users.read")),
):
    """
    Get a specific department by ID.
    """
    department = db.query(Department).filter(Department.id == department_id).first()
    if not department:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Department not found",
        )
    return department


@router.post("", response_model=DepartmentResponse, status_code=status.HTTP_201_CREATED)
async def create_department(
    department_data: DepartmentCreate,
    db: Session = Depends(get_db),
    current_user: User = Depends(require_system_admin),
):
    """
    Create a new department. Requires system admin.
    """
    # Check if parent exists if specified
    if department_data.parent_id:
        parent = db.query(Department).filter(
            Department.id == department_data.parent_id
        ).first()
        if not parent:
            raise HTTPException(
                status_code=status.HTTP_404_NOT_FOUND,
                detail="Parent department not found",
            )

    department = Department(**department_data.model_dump())
    db.add(department)
    db.commit()
    db.refresh(department)
    return department


@router.patch("/{department_id}", response_model=DepartmentResponse)
async def update_department(
    department_id: str,
    department_update: DepartmentUpdate,
    db: Session = Depends(get_db),
    current_user: User = Depends(require_system_admin),
):
    """
    Update a department. Requires system admin.
    """
    department = db.query(Department).filter(Department.id == department_id).first()
    if not department:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Department not found",
        )

    # Check if new parent exists if specified
    update_data = department_update.model_dump(exclude_unset=True)
    if "parent_id" in update_data and update_data["parent_id"]:
        # Prevent circular reference
        if update_data["parent_id"] == department_id:
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail="Department cannot be its own parent",
            )

        parent = db.query(Department).filter(
            Department.id == update_data["parent_id"]
        ).first()
        if not parent:
            raise HTTPException(
                status_code=status.HTTP_404_NOT_FOUND,
                detail="Parent department not found",
            )

    for field, value in update_data.items():
        setattr(department, field, value)

    db.commit()
    db.refresh(department)
    return department


@router.delete("/{department_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_department(
    department_id: str,
    db: Session = Depends(get_db),
    current_user: User = Depends(require_system_admin),
):
    """
    Delete a department. Requires system admin.
    """
    department = db.query(Department).filter(Department.id == department_id).first()
    if not department:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Department not found",
        )

    # Check if department has users
    user_count = db.query(User).filter(User.department_id == department_id).count()
    if user_count > 0:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail=f"Cannot delete department with {user_count} users",
        )

    # Check if department has children
    child_count = db.query(Department).filter(
        Department.parent_id == department_id
    ).count()
    if child_count > 0:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail=f"Cannot delete department with {child_count} child departments",
        )

    db.delete(department)
    db.commit()