Added WhatsApp (not activated) + rearranged sources

lib/app_sources/whatsapp.dart

@@ -0,0 +1,75 @@
+import 'package:html/parser.dart';
+import 'package:http/http.dart';
+import 'package:obtainium/custom_errors.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class WhatsApp extends AppSource {
+  WhatsApp() {
+    host = 'whatsapp.com';
+  }
+
+  @override
+  String standardizeURL(String url) {
+    return 'https://$host';
+  }
+
+  @override
+  Future<String> apkUrlPrefetchModifier(String apkUrl) async {
+    Response res = await get(Uri.parse('https://www.whatsapp.com/android'));
+    if (res.statusCode == 200) {
+      var targetLinks = parse(res.body)
+          .querySelectorAll('a')
+          .map((e) => e.attributes['href'])
+          .where((e) => e != null)
+          .where((e) =>
+              e!.contains('scontent.whatsapp.net') &&
+              e.contains('WhatsApp.apk'))
+          .toList();
+      if (targetLinks.isEmpty) {
+        throw NoAPKError();
+      }
+      return targetLinks[0]!;
+    } else {
+      throw getObtainiumHttpError(res);
+    }
+  }
+
+  @override
+  Future<APKDetails> getLatestAPKDetails(
+    String standardUrl,
+    Map<String, dynamic> additionalSettings,
+  ) async {
+    Response res = await get(Uri.parse('https://www.whatsapp.com/android'));
+    if (res.statusCode == 200) {
+      var targetElements = parse(res.body)
+          .querySelectorAll('p')
+          .where((element) => element.innerHtml.contains('Version '))
+          .toList();
+      if (targetElements.isEmpty) {
+        throw NoVersionError();
+      }
+      var vLines = targetElements[0]
+          .innerHtml
+          .split('\n')
+          .where((element) => element.contains('Version '))
+          .toList();
+      if (vLines.isEmpty) {
+        throw NoVersionError();
+      }
+      var versionMatch = RegExp('[0-9]+(\\.[0-9]+)+').firstMatch(vLines[0]);
+      if (versionMatch == null) {
+        throw NoVersionError();
+      }
+      String version =
+          vLines[0].substring(versionMatch.start, versionMatch.end);
+      return APKDetails(
+          version,
+          [
+            'https://www.whatsapp.com/android?v=$version&=thisIsaPlaceholder&a=realURLPrefetchedAtDownloadTime'
+          ],
+          AppNames('Meta', 'WhatsApp'));
+    } else {
+      throw getObtainiumHttpError(res);
+    }
+  }
+}