Moved App Sources into separate files

lib/app_sources/github.dart

@@ -0,0 +1,70 @@
+import 'dart:convert';
+import 'package:http/http.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class GitHub implements AppSource {
+  @override
+  late String host = 'github.com';
+
+  @override
+  String standardizeURL(String url) {
+    RegExp standardUrlRegEx = RegExp('^https?://$host/[^/]+/[^/]+');
+    RegExpMatch? match = standardUrlRegEx.firstMatch(url.toLowerCase());
+    if (match == null) {
+      throw notValidURL;
+    }
+    return url.substring(0, match.end);
+  }
+
+  @override
+  Future<APKDetails> getLatestAPKDetails(String standardUrl) async {
+    Response res = await get(Uri.parse(
+        'https://api.$host/repos${standardUrl.substring('https://$host'.length)}/releases'));
+    if (res.statusCode == 200) {
+      var releases = jsonDecode(res.body) as List<dynamic>;
+      // Right now, the latest non-prerelease version is picked
+      // If none exists, the latest prerelease version is picked
+      // In the future, the user could be given a choice
+      var nonPrereleaseReleases =
+          releases.where((element) => element['prerelease'] != true).toList();
+      var latestRelease = nonPrereleaseReleases.isNotEmpty
+          ? nonPrereleaseReleases[0]
+          : releases.isNotEmpty
+              ? releases[0]
+              : null;
+      if (latestRelease == null) {
+        throw couldNotFindReleases;
+      }
+      List<dynamic>? assets = latestRelease['assets'];
+      List<String>? apkUrlList = assets
+          ?.map((e) {
+            return e['browser_download_url'] != null
+                ? e['browser_download_url'] as String
+                : '';
+          })
+          .where((element) => element.toLowerCase().endsWith('.apk'))
+          .toList();
+      if (apkUrlList == null || apkUrlList.isEmpty) {
+        throw noAPKFound;
+      }
+      String? version = latestRelease['tag_name'];
+      if (version == null) {
+        throw couldNotFindLatestVersion;
+      }
+      return APKDetails(version, apkUrlList);
+    } 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 couldNotFindReleases;
+    }
+  }
+
+  @override
+  AppNames getAppNames(String standardUrl) {
+    String temp = standardUrl.substring(standardUrl.indexOf('://') + 3);
+    List<String> names = temp.substring(temp.indexOf('/') + 1).split('/');
+    return AppNames(names[0], names[1]);
+  }
+}