Added Steam as a Source (#159) + Bugfixes

lib/app_sources/steammobile.dart

@@ -0,0 +1,69 @@
+import 'package:easy_localization/easy_localization.dart';
+import 'package:html/parser.dart';
+import 'package:http/http.dart';
+import 'package:obtainium/components/generated_form.dart';
+import 'package:obtainium/custom_errors.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class SteamMobile extends AppSource {
+  SteamMobile() {
+    host = 'store.steampowered.com';
+    name = tr('steam');
+    additionalSourceAppSpecificFormItems = [
+      [
+        GeneratedFormItem(
+            label: tr('app'),
+            key: 'app',
+            required: true,
+            opts: apks.entries.toList())
+      ]
+    ];
+  }
+
+  final apks = {'steam': tr('steamMobile'), 'steam-chat-app': tr('steamChat')};
+
+  @override
+  String standardizeURL(String url) {
+    return 'https://$host';
+  }
+
+  @override
+  String? changeLogPageFromStandardUrl(String standardUrl) => null;
+
+  @override
+  Future<APKDetails> getLatestAPKDetails(
+      String standardUrl, List<String> additionalData,
+      {bool trackOnly = false}) async {
+    Response res = await get(Uri.parse('https://$host/mobile'));
+    if (res.statusCode == 200) {
+      var apkNamePrefix = findGeneratedFormValueByKey(
+          additionalSourceAppSpecificFormItems
+              .reduce((value, element) => [...value, ...element]),
+          additionalData,
+          'app');
+      if (apkNamePrefix == null) {
+        throw NoReleasesError();
+      }
+      String apkInURLRegexPattern = '/$apkNamePrefix-[^/]+\\.apk\$';
+      var links = parse(res.body)
+          .querySelectorAll('a')
+          .map((e) => e.attributes['href'] ?? '')
+          .where((e) => RegExp('https://.*$apkInURLRegexPattern').hasMatch(e))
+          .toList();
+
+      if (links.isEmpty) {
+        throw NoReleasesError();
+      }
+      var versionMatch = RegExp(apkInURLRegexPattern).firstMatch(links[0]);
+      if (versionMatch == null) {
+        throw NoVersionError();
+      }
+      var version = links[0].substring(
+          versionMatch.start + apkNamePrefix.length + 2, versionMatch.end - 4);
+      var apkUrls = [links[0]];
+      return APKDetails(version, apkUrls, AppNames(name, apks[apkNamePrefix]!));
+    } else {
+      throw NoReleasesError();
+    }
+  }
+}