// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library shelf_cors;

import 'package:shelf/shelf.dart';

// TODO: Rename to createCorsHeadersMiddleware or corsHeadersMiddleware?

/// Middleware which adds [CORS headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS)
/// to shelf responses. Also handles preflight (OPTIONS) requests.
Middleware createCorsHeadersMiddleware({Map<String, String> corsHeaders}) {
  // By default allow access from everywhere.
  corsHeaders ??= <String, String>{'Access-Control-Allow-Origin': '*'};

  // Handle preflight (OPTIONS) requests by just adding headers and an empty
  // response.
  Response handleOptionsRequest(Request request) {
    if (request.method == 'OPTIONS') {
      return Response.ok(null, headers: corsHeaders);
    } else {
      return null;
    }
  }

  Response addCorsHeaders(Response response) =>
      response?.change(headers: corsHeaders);

  return createMiddleware(
      requestHandler: handleOptionsRequest, responseHandler: addCorsHeaders);
}