cleanplate_api/lib/src/middleware/error_handler.dart

import 'dart:convert';
import 'package:shelf/shelf.dart';
import 'package:logging/logging.dart';

final _log = Logger('ErrorHandler');

/// Global error-handling middleware.
///
/// Catches synchronous and asynchronous exceptions thrown by inner handlers
/// and converts them to structured JSON error responses.
Middleware errorHandler() {
  return (Handler innerHandler) {
    return (Request request) async {
      try {
        final response = await innerHandler(request);
        return response;
      } on ApiException catch (e) {
        _log.warning('API error: ${e.code} - ${e.message}');
        return Response(e.statusCode,
            headers: {'content-type': 'application/json'},
            body: jsonEncode({
              'status': 'error',
              'error': {
                'code': e.code,
                'message': e.message,
                if (e.details != null) 'details': e.details,
              },
            }));
      } on FormatException catch (e) {
        _log.warning('Bad request: $e');
        return Response(400,
            headers: {'content-type': 'application/json'},
            body: jsonEncode({
              'status': 'error',
              'error': {
                'code': 'BAD_REQUEST',
                'message': 'Invalid request format: ${e.message}',
              },
            }));
      } catch (e, st) {
        _log.severe('Unhandled exception', e, st);
        return Response.internalServerError(
          headers: {'content-type': 'application/json'},
          body: jsonEncode({
            'status': 'error',
            'error': {
              'code': 'INTERNAL_ERROR',
              'message': 'Internal server error',
            },
          }),
        );
      }
    };
  };
}

/// A typed exception that the error handler can inspect to produce a proper
/// HTTP status and machine-readable error code.
class ApiException implements Exception {
  final int statusCode;
  final String code;
  final String message;
  final dynamic details;

  ApiException(this.statusCode, this.code, this.message, {this.details});

  factory ApiException.badRequest(String message, {dynamic details}) =>
      ApiException(400, 'BAD_REQUEST', message, details: details);

  factory ApiException.unauthorized([String message = 'Unauthorized']) =>
      ApiException(401, 'UNAUTHORIZED', message);

  factory ApiException.forbidden([String message = 'Forbidden']) =>
      ApiException(403, 'FORBIDDEN', message);

  factory ApiException.notFound([String message = 'Not found']) =>
      ApiException(404, 'NOT_FOUND', message);

  factory ApiException.conflict(String message) =>
      ApiException(409, 'CONFLICT', message);

  factory ApiException.tooManyRequests([String message = 'Too many requests']) =>
      ApiException(429, 'TOO_MANY_REQUESTS', message);

  factory ApiException.internal([String message = 'Internal server error']) =>
      ApiException(500, 'INTERNAL_ERROR', message);

  @override
  String toString() => 'ApiException($statusCode, $code, $message)';
}