Moved App Sources into separate files

lib/mass_app_sources/githubstars.dart

@@ -0,0 +1,32 @@
+import 'dart:convert';
+
+import 'package:http/http.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class GitHubStars implements MassAppSource {
+  @override
+  late String name = 'GitHub Starred Repos';
+
+  @override
+  late List<String> requiredArgs = ['Username'];
+
+  @override
+  Future<List<String>> getUrls(List<String> args) async {
+    if (args.length != requiredArgs.length) {
+      throw 'Wrong number of arguments provided';
+    }
+    Response res =
+        await get(Uri.parse('https://api.github.com/users/${args[0]}/starred'));
+    if (res.statusCode == 200) {
+      return (jsonDecode(res.body) as List<dynamic>)
+          .map((e) => e['html_url'] as String)
+          .toList();
+    } else {
+      if (res.headers['x-ratelimit-remaining'] == '0') {
+        throw 'Rate limit reached - try again in ${(int.parse(res.headers['x-ratelimit-reset'] ?? '1800000000') / 60000000).toString()} minutes';
+      }
+
+      throw 'Unable to find user\'s starred repos';
+    }
+  }
+}