Dart formatting sample

twitter.dart

import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:convert/convert.dart';
import 'package:crypto/crypto.dart';

const String twitterApiBaseUrl = "https://api.twitter.com/1.1/";

class TwitterApi {
  final String consumerKey, consumerKeySecret, accessToken, accessTokenSecret;
  Hmac _sigHasher; 
  final DateTime _epochUtc = new DateTime(1970, 1, 1);

  TwitterApi(this.consumerKey, this.consumerKeySecret, this.accessToken, this.accessTokenSecret) {
    _sigHasher = new Hmac(sha1, UTF8.encode("$consumerKeySecret&$accessTokenSecret"));
  }

  /// Sends a tweet with the supplied text and returns the response from the Twitter API.
  Future<String> tweet(String text) {
    var data = {"status": text, "trim_user": "1"};

    return _callApi("statuses/update.json", data);
  }

  Future<String> _callApi(String url, Map<String, String> data) {
    var fullUrl = Uri.parse(twitterApiBaseUrl + url);

    // Timestamps are in seconds since 1/1/1970.
    var timestamp = new DateTime.now().toUtc().difference(_epochUtc).inSeconds;

    // Add all the OAuth headers we'll need to use when constructing the hash.
    data["oauth_consumer_key"] = consumerKey;
    data["oauth_signature_method"] = "HMAC-SHA1";
    data["oauth_timestamp"] = timestamp.toString();
    data["oauth_nonce"] = "a"; // Required, but Twitter doesn't appear to use it, so "a" will do.
    data["oauth_token"] = accessToken;
    data["oauth_version"] = "1.0";

    // Generate the OAuth signature and add it to our payload.
    data["oauth_signature"] = _generateSignature(fullUrl, data);

    // Build the OAuth HTTP Header from the data.
    var oAuthHeader = _generateOAuthHeader(data);

    // Build the form data (exclude OAuth stuff that's already in the header).
    var formData = filterMap(data, (k) => !k.startsWith("oauth_"));

    return _sendRequest(fullUrl, oAuthHeader, toQueryString(formData));
  }

  /// Generate an OAuth signature from OAuth header values.
  String _generateSignature(Uri url, Map<String, String> data) {
    var sigString = toQueryString(data);
    var fullSigData = "POST&${encode(url.toString())}&${encode(sigString)}";
    
    return BASE64.encode(hash(fullSigData));
  }

  /// Generate the raw OAuth HTML header from the values (including signature).
  String _generateOAuthHeader(Map<String, String> data) {
    var oauthHeaderValues = filterMap(data, (k) => k.startsWith("oauth_"));

    return "OAuth " + toOAuthHeader(oauthHeaderValues);
  }

  /// Send HTTP Request and return the response.
  Future<String> _sendRequest(Uri fullUrl, String oAuthHeader, String body) async {
    var http = new HttpClient();
    return http.postUrl(fullUrl).then((HttpClientRequest request) {
      request.headers.contentType = new ContentType("application", "x-www-form-urlencoded", charset: "utf-8");
      request.headers.add("Authorization", oAuthHeader);
      request.write(body);
      return request.close();
    }).then((HttpClientResponse response) {
      return response.transform(UTF8.decoder).join("");
    });
  }

  Map<String, String> filterMap(Map<String, String> map, bool test(String key)) {
    return new Map.fromIterable(map.keys.where(test), value: (k) => map[k]);
  }

  String toQueryString(Map<String, String> data) {
    var items = data
      .keys
      .map((k) => "$k=${encode(data[k])}")
      .toList()
      ..sort();

    return items.join("&");
  }

  String toOAuthHeader(Map<String, String> data) {
    var items = data
      .keys
      .map((k) => "$k=\"${encode(data[k])}\"")
      .toList()
      ..sort();

    return items.join(", ");
  }

  List<int> hash(String data) => _sigHasher.convert(data.codeUnits).bytes;

  // TODO: Remove this hacky crap when percentEncode is fixed.
  String encode(String data) {
    return percent.encode(data.codeUnits)
      .replaceAll('%30', '0')
      .replaceAll('%31', '1')
      .replaceAll('%32', '2')
      .replaceAll('%33', '3')
      .replaceAll('%34', '4')
      .replaceAll('%35', '5')
      .replaceAll('%36', '6')
      .replaceAll('%37', '7')
      .replaceAll('%38', '8')
      .replaceAll('%39', '9')
      .replaceAll('=', '%3D');
  }
}