+ (void)getRequestTokenWithCompletion:(void (^)(NSString *requestToken,
                                                NSError *error))completionBlock {

  NSString *consumerKey = [[self class] consumerKey];
  NSString *consumerSecret = [[self class] consumerSecret];

  NSDictionary *parameters = @{@"x_auth_mode" : @"reverse_auth"};

  NSMutableString *paramsAsString = [[NSMutableString alloc] init];
  [parameters enumerateKeysAndObjectsUsingBlock: ^(id key, id obj, BOOL *stop) {
    [paramsAsString appendFormat:@"%@=%@&", key, obj];
  }];

  NSURL *url = [NSURL URLWithString:@"https://api.twitter.com/oauth/request_token"];

  NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url];
  request.HTTPMethod = @"POST";
  request.HTTPBody = [paramsAsString dataUsingEncoding:NSUTF8StringEncoding];

  NSString *authorizationHeader = OAuthorizationHeader(request.URL,
                                                       request.HTTPMethod,
                                                       request.HTTPBody,
                                                       consumerKey,
                                                       consumerSecret, nil, nil);

  [request setValue:authorizationHeader forHTTPHeaderField:@"Authorization"];

  [NSURLConnection sendAsynchronousRequest:request
                                     queue:[NSOperationQueue mainQueue]
                         completionHandler:^(NSURLResponse *response,
                                             NSData *data,
                                             NSError *connectionError) {

                           NSString *requestToken =
                             [[NSString alloc] initWithData:data
                                                   encoding:NSUTF8StringEncoding];
                           if (completionBlock) {
                             completionBlock(requestToken, connectionError);
                           }
                         }];
}


+ (void)getAccessTokenForAccount:(ACAccount *)twitterAccount
                withRequestToken:(NSString *)requestToken
                      completion:(void (^)(NSString *accessToken,
                                           NSError *error))completionBlock {


  NSDictionary *parameters = @{
    @"x_reverse_auth_parameters" : requestToken,
    @"x_reverse_auth_target"     : [[self class] consumerKey]
  };

  NSURL *url = [NSURL URLWithString:@"https://api.twitter.com/oauth/access_token"];

  SLRequest *request = [SLRequest requestForServiceType:SLServiceTypeTwitter
                                          requestMethod:SLRequestMethodPOST
                                                    URL:url
                                             parameters:parameters];
  [request setAccount:twitterAccount];

  [request performRequestWithHandler:^(NSData *responseData,
                                       NSHTTPURLResponse *urlResponse,
                                       NSError *error) {

    NSString *responseStr = [[NSString alloc] initWithData:responseData
                                                  encoding:NSUTF8StringEncoding];

    if (completionBlock) {
      completionBlock(responseStr, error);
    }
  }];
}


#pragma mark - Credentials

+ (NSString *)consumerKey {

  static NSString *consumerKey;
  if (consumerKey == nil) {
    consumerKey = @"bla-bl-bla";
  }

  return consumerKey;
}

+ (NSString *)consumerSecret {

  static NSString *consumerSecret;
  if (consumerSecret == nil) {
    consumerSecret = @"bla-bla-bla";
  }
  return consumerSecret;
}