// Copyright (c) 2012, 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.

import 'dart:async';

import 'package:http/http.dart' as http;
import 'package:http_parser/http_parser.dart';

import 'client.dart';
import 'handle_access_token_response.dart';
import 'utils.dart';

/// Obtains credentials using a [client credentials grant](https://tools.ietf.org/html/rfc6749#section-1.3.4).
///
/// This mode of authorization uses the client's [identifier] and [secret]
/// to obtain an authorization token from the authorization server, instead
/// of sending a user through a dedicated flow.
///
/// The client [identifier] and [secret] are required, and are
/// used to identify and authenticate your specific OAuth2 client. These are
/// usually global to the program using this library.
///
/// The specific permissions being requested from the authorization server may
/// be specified via [scopes]. The scope strings are specific to the
/// authorization server and may be found in its documentation. Note that you
/// may not be granted access to every scope you request; you may check the
/// [Credentials.scopes] field of [Client.credentials] to see which scopes you
/// were granted.
///
/// The scope strings will be separated by the provided [delimiter]. This
/// defaults to `" "`, the OAuth2 standard, but some APIs (such as Facebook's)
/// use non-standard delimiters.
///
/// By default, this follows the OAuth2 spec and requires the server's responses
/// to be in JSON format. However, some servers return non-standard response
/// formats, which can be parsed using the [getParameters] function.
///
/// This function is passed the `Content-Type` header of the response as well as
/// its body as a UTF-8-decoded string. It should return a map in the same
/// format as the [standard JSON response](https://tools.ietf.org/html/rfc6749#section-5.1)
Future<Client> clientCredentialsGrant(
    Uri authorizationEndpoint, String identifier, String secret,
    {Iterable<String> scopes,
    bool basicAuth = true,
    http.Client httpClient,
    String delimiter,
    Map<String, dynamic> getParameters(
        MediaType contentType, String body)}) async {
  delimiter ??= ' ';
  var startTime = new DateTime.now();

  var body = {"grant_type": "client_credentials"};

  var headers = <String, String>{};

  if (identifier != null) {
    if (basicAuth) {
      headers['Authorization'] = basicAuthHeader(identifier, secret);
    } else {
      body['client_id'] = identifier;
      if (secret != null) body['client_secret'] = secret;
    }
  }

  if (scopes != null && scopes.isNotEmpty)
    body['scope'] = scopes.join(delimiter);

  if (httpClient == null) httpClient = new http.Client();
  var response = await httpClient.post(authorizationEndpoint,
      headers: headers, body: body);

  var credentials = await handleAccessTokenResponse(
      response, authorizationEndpoint, startTime, scopes, delimiter,
      getParameters: getParameters);
  return new Client(credentials,
      identifier: identifier, secret: secret, httpClient: httpClient);
}