import uuid
import logging

from rest_framework.views import exception_handler as drf_exception_handler
from rest_framework.response import Response
from rest_framework.exceptions import APIException, ValidationError

logger = logging.getLogger(__name__)

_STATUS_TO_CODE = {
    400: 'BAD_REQUEST',
    401: 'AUTH_UNAUTHORIZED',
    403: 'PERMISSION_DENIED',
    404: 'NOT_FOUND',
    405: 'METHOD_NOT_ALLOWED',
    429: 'SYS_RATE_LIMIT',
    500: 'SYS_INTERNAL',
    503: 'SYS_DEPENDENCY_DOWN',
}


def custom_exception_handler(exc, context):
    trace_id = uuid.uuid4().hex[:12]
    response = drf_exception_handler(exc, context)

    if response is None:
        logger.exception('Unhandled server error trace_id=%s', trace_id)
        return Response(
            {'code': 'SYS_INTERNAL', 'message': '服务器内部错误', 'details': None, 'trace_id': trace_id},
            status=500,
        )

    data = response.data
    status_code = response.status_code

    # Already structured by AppError or our custom exceptions
    if isinstance(data, dict) and 'code' in data and 'message' in data:
        response.data = {**data, 'trace_id': trace_id}
        return response

    # DRF ValidationError: {'field': ['error msg']}
    if isinstance(exc, ValidationError):
        response.data = {
            'code': 'VALIDATION_ERROR',
            'message': '请求参数不合法',
            'details': data,
            'trace_id': trace_id,
        }
        return response

    # Standard DRF exceptions (AuthenticationFailed, PermissionDenied, Throttled, etc.)
    message = _extract_message(data)
    response.data = {
        'code': _STATUS_TO_CODE.get(status_code, 'SYS_INTERNAL'),
        'message': message,
        'details': None,
        'trace_id': trace_id,
    }
    return response


def _extract_message(data):
    if isinstance(data, dict):
        return str(data.get('detail', data))
    if isinstance(data, list) and data:
        return str(data[0])
    return str(data)


class AppError(APIException):
    """统一业务异常。视图中 raise AppError('CODE', '消息', details, status_code) 即可。"""

    def __init__(self, code, message, details=None, status_code=400):
        self.status_code = status_code
        super().__init__(detail=code)
        # 绕过 DRF _get_error_details，防止 None 被转成字符串 "None"
        self.detail = {'code': code, 'message': message, 'details': details}