from apps.user.models import Department
from config.exceptions import AppError


def resolve_department(department_name: str):
    """按名称解析科室，返回 Department 实例。

    - 空/None → 返回 None（不强制）
    - 精确匹配 1 条 → 返回该 Department
    - 匹配 0 条 → 400 CASE_DEPARTMENT_NOT_FOUND
    - 匹配多条 → 400 CASE_DEPARTMENT_AMBIGUOUS
    """
    if not department_name:
        return None

    qs = Department.objects.filter(name=department_name)
    count = qs.count()

    if count == 0:
        raise AppError(
            'CASE_DEPARTMENT_NOT_FOUND',
            f'科室 "{department_name}" 不存在',
            status_code=400,
        )
    if count > 1:
        raise AppError(
            'CASE_DEPARTMENT_AMBIGUOUS',
            f'科室 "{department_name}" 匹配到多条记录，请精确指定',
            details={'matches': list(qs.values_list('name', flat=True))},
            status_code=400,
        )
    return qs.first()