channel description

lib/src/channels/channel.dart

@@ -13,11 +13,14 @@ class Channel with EquatableMixin {
   /// Channel title.
   final String title;
 
+  /// Channel description
+  final String description;
+
   /// URL of the channel's logo image.
   final String logoUrl;
 
   /// Initializes an instance of [Channel]
-  Channel(this.id, this.title, this.logoUrl);
+  Channel(this.id, this.title, this.description, this.logoUrl);
 
   @override
   String toString() => 'Channel ($title)';

lib/src/channels/channel_about.dart

@@ -0,0 +1,13 @@
+import 'package:equatable/equatable.dart';
+
+/// YouTube channel about metadata.
+class ChannelAbout with EquatableMixin {
+  /// Channel description.
+  final String description;
+
+  /// Initializes an instance of [ChannelAbout]
+  ChannelAbout(this.description);
+
+  @override
+  List<Object> get props => [description];
+}

lib/src/channels/channel_client.dart

@@ -1,5 +1,6 @@
 import '../extensions/helpers_extension.dart';
 import '../playlists/playlists.dart';
+import '../reverse_engineering/responses/channel_about_page.dart';
 import '../reverse_engineering/responses/channel_upload_page.dart';
 import '../reverse_engineering/responses/responses.dart';
 import '../reverse_engineering/youtube_http_client.dart';
@@ -24,8 +25,10 @@ class ChannelClient {
   Future<Channel> get(dynamic id) async {
     id = ChannelId.fromString(id);
     var channelPage = await ChannelPage.get(_httpClient, id.value);
+    var channelAboutPage = await ChannelAboutPage.get(_httpClient, id.value);
 
-    return Channel(id, channelPage.channelTitle, channelPage.channelLogoUrl);
+    return Channel(id, channelPage.channelTitle, channelAboutPage.description,
+        channelPage.channelLogoUrl);
   }
 
   /// Gets the metadata associated with the channel of the specified user.
@@ -36,8 +39,11 @@ class ChannelClient {
 
     var channelPage =
         await ChannelPage.getByUsername(_httpClient, username.value);
+    var channelAboutPage =
+        await ChannelAboutPage.getByUsername(_httpClient, username.value);
+
     return Channel(ChannelId(channelPage.channelId), channelPage.channelTitle,
-        channelPage.channelLogoUrl);
+        channelAboutPage.description, channelPage.channelLogoUrl);
   }
 
   /// Gets the metadata associated with the channel

lib/src/reverse_engineering/responses/channel_about_page.dart

@@ -0,0 +1,113 @@
+import 'dart:convert';
+
+import 'package:html/dom.dart';
+import 'package:html/parser.dart' as parser;
+
+import '../../exceptions/exceptions.dart';
+import '../../extensions/helpers_extension.dart';
+import '../../retry.dart';
+import '../youtube_http_client.dart';
+
+///
+class ChannelAboutPage {
+  final Document _root;
+
+  _InitialData _initialData;
+
+  ///
+  _InitialData get initialData =>
+      _initialData ??= _InitialData(json.decode(_matchJson(_extractJson(
+          _root
+              .querySelectorAll('script')
+              .map((e) => e.text)
+              .toList()
+              .firstWhere((e) => e.contains('window["ytInitialData"] =')),
+          'window["ytInitialData"] ='))));
+
+  ///
+  bool get isOk => initialData != null;
+
+  ///
+  String get description => initialData.description;
+
+  String _extractJson(String html, String separator) {
+    return _matchJson(
+        html.substring(html.indexOf(separator) + separator.length));
+  }
+
+  String _matchJson(String str) {
+    var bracketCount = 0;
+    int lastI;
+    for (var i = 0; i < str.length; i++) {
+      lastI = i;
+      if (str[i] == '{') {
+        bracketCount++;
+      } else if (str[i] == '}') {
+        bracketCount--;
+      } else if (str[i] == ';') {
+        if (bracketCount == 0) {
+          return str.substring(0, i);
+        }
+      }
+    }
+    return str.substring(0, lastI + 1);
+  }
+
+  ///
+  ChannelAboutPage(this._root);
+
+  ///
+  ChannelAboutPage.parse(String raw) : _root = parser.parse(raw);
+
+  ///
+  static Future<ChannelAboutPage> get(YoutubeHttpClient httpClient, String id) {
+    var url = 'https://www.youtube.com/channel/$id/about?hl=en';
+
+    return retry(() async {
+      var raw = await httpClient.getString(url);
+      var result = ChannelAboutPage.parse(raw);
+
+      if (!result.isOk) {
+        throw TransientFailureException('Channel about page is broken');
+      }
+      return result;
+    });
+  }
+
+  ///
+  static Future<ChannelAboutPage> getByUsername(
+      YoutubeHttpClient httpClient, String username) {
+    var url = 'https://www.youtube.com/user/$username/about?hl=en';
+
+    return retry(() async {
+      var raw = await httpClient.getString(url);
+      var result = ChannelAboutPage.parse(raw);
+
+      if (!result.isOk) {
+        throw TransientFailureException('Channel about page is broken');
+      }
+      return result;
+    });
+  }
+}
+
+class _InitialData {
+  // Json parsed map
+  final Map<String, dynamic> root;
+
+  _InitialData(this.root);
+
+  /* Cache results */
+
+  String _description;
+
+  Map<String, dynamic> getDescriptionContext(Map<String, dynamic> root) {
+    if (root['metadata'] != null) {
+      return root['metadata']['channelMetadataRenderer'];
+    }
+    return null;
+  }
+
+  String get description => _description ??=
+      getDescriptionContext(root)?.getValue('description') ?? '';
+}