from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy import func, select, update
from sqlalchemy.orm import Session

from app.db import get_db
from app.deps import require_admin
from app.models import Unit, User
from app.schemas.unit import UnitCreate, UnitResponse, UnitUpdate
from app.services.audit_service import write_audit

router = APIRouter()


def _serialize(unit: Unit, user_count: int) -> UnitResponse:
    return UnitResponse(
        id=unit.id,
        name=unit.name,
        description=unit.description,
        parent_id=unit.parent_id,
        category=unit.category or "company",
        user_count=user_count,
    )


def _validate_parent(
    db: Session,
    parent_id: int | None,
    self_id: int | None,
    category: str | None = None,
) -> None:
    if parent_id is None:
        return
    if self_id is not None and parent_id == self_id:
        raise HTTPException(status_code=400, detail="上级单位不能是自身")
    parent = db.get(Unit, parent_id)
    if not parent:
        raise HTTPException(status_code=404, detail="上级单位不存在")
    if category == "company" and (parent.category or "company") != "company":
        raise HTTPException(status_code=400, detail="公司只能挂在公司下")
    if self_id is not None:
        current = parent
        while current is not None:
            if current.id == self_id:
                raise HTTPException(status_code=400, detail="上级单位不能是自身的下级")
            current = db.get(Unit, current.parent_id) if current.parent_id else None


@router.get("", response_model=list[UnitResponse])
def list_units(db: Session = Depends(get_db), _: User = Depends(require_admin)) -> list[UnitResponse]:
    counts = dict(db.execute(
        select(User.unit_id, func.count(User.id))
        .where(User.unit_id.is_not(None))
        .group_by(User.unit_id)
    ).all())
    units = db.scalars(select(Unit).order_by(Unit.id)).all()
    return [_serialize(u, counts.get(u.id, 0)) for u in units]


@router.post("", response_model=UnitResponse)
def create_unit(
    payload: UnitCreate,
    db: Session = Depends(get_db),
    admin: User = Depends(require_admin),
) -> UnitResponse:
    if db.scalar(select(Unit).where(Unit.name == payload.name)):
        raise HTTPException(status_code=409, detail="单位名称已存在")
    _validate_parent(db, payload.parent_id, None, payload.category)
    unit = Unit(
        name=payload.name,
        description=payload.description,
        parent_id=payload.parent_id,
        category=payload.category,
    )
    db.add(unit)
    db.flush()
    write_audit(db, "unit.create", actor_id=admin.id, target_type="unit", target_id=str(unit.id))
    db.commit()
    db.refresh(unit)
    return _serialize(unit, 0)


@router.patch("/{unit_id}", response_model=UnitResponse)
def update_unit(
    unit_id: int,
    payload: UnitUpdate,
    db: Session = Depends(get_db),
    admin: User = Depends(require_admin),
) -> UnitResponse:
    unit = db.get(Unit, unit_id)
    if not unit:
        raise HTTPException(status_code=404, detail="单位不存在")
    if payload.name is not None and payload.name != unit.name:
        if db.scalar(select(Unit).where(Unit.name == payload.name, Unit.id != unit.id)):
            raise HTTPException(status_code=409, detail="单位名称已存在")
        unit.name = payload.name
    if payload.description is not None:
        unit.description = payload.description
    fields_set = payload.model_fields_set
    new_category = payload.category if payload.category is not None else (unit.category or "company")
    if "parent_id" in fields_set:
        _validate_parent(db, payload.parent_id, unit.id, new_category)
        unit.parent_id = payload.parent_id
    elif payload.category is not None and payload.category != unit.category:
        # 分类变化时校验原有父级仍然合法
        _validate_parent(db, unit.parent_id, unit.id, new_category)
    if payload.category is not None:
        unit.category = payload.category
    write_audit(db, "unit.update", actor_id=admin.id, target_type="unit", target_id=str(unit.id))
    db.commit()
    db.refresh(unit)
    user_count = db.scalar(select(func.count(User.id)).where(User.unit_id == unit.id)) or 0
    return _serialize(unit, user_count)


@router.delete("/{unit_id}")
def delete_unit(
    unit_id: int,
    db: Session = Depends(get_db),
    admin: User = Depends(require_admin),
) -> dict:
    unit = db.get(Unit, unit_id)
    if not unit:
        raise HTTPException(status_code=404, detail="单位不存在")
    if db.scalar(select(func.count(Unit.id)).where(Unit.parent_id == unit_id)):
        raise HTTPException(status_code=400, detail="请先删除或转移下级单位")
    db.execute(update(User).where(User.unit_id == unit_id).values(unit_id=None))
    write_audit(db, "unit.delete", actor_id=admin.id, target_type="unit", target_id=str(unit_id),
                detail={"name": unit.name})
    db.delete(unit)
    db.commit()
    return {"deleted": True, "id": unit_id}