focusflow_api/lib/src/middleware/error_handler.dart

import 'dart:convert';

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

final _log = Logger('ErrorHandler');

// ── ApiException ──────────────────────────────────────────────────────

/// Typed exception that maps directly to an HTTP status code.
class ApiException implements Exception {
  final int statusCode;
  final String message;
  final dynamic errors;

  const ApiException(this.statusCode, this.message, {this.errors});

  // Factory constructors for common HTTP errors
  factory ApiException.badRequest(String message, {dynamic errors}) =>
      ApiException(400, message, errors: errors);

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

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

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

  factory ApiException.conflict([String message = 'Conflict']) =>
      ApiException(409, message);

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

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

// ── Middleware ─────────────────────────────────────────────────────────

/// Catches all exceptions and returns a consistent JSON error response.
Middleware errorHandlerMiddleware() {
  return (Handler innerHandler) {
    return (Request request) async {
      try {
        return await innerHandler(request);
      } on ApiException catch (e) {
        return _jsonError(e.statusCode, e.message, errors: e.errors);
      } catch (e, st) {
        _log.severe('Unhandled exception', e, st);
        return _jsonError(500, 'Internal server error');
      }
    };
  };
}

Response _jsonError(int statusCode, String message, {dynamic errors}) {
  return Response(
    statusCode,
    body: jsonEncode({
      'success': false,
      'message': message,
      if (errors != null) 'errors': errors,
    }),
    headers: {'Content-Type': 'application/json'},
  );
}