claude refactorings, flutter best practices, platform dependent changes, general cleanup

lib/utils/file_downloader.dart

@@ -0,0 +1,47 @@
+import 'package:dio/dio.dart';
+
+/// Lightweight cancel handle around a single `Dio.download` call. The download
+/// itself is started by [run]; the handle returns synchronously so callers can
+/// install it into shared state before the first progress event can fire.
+class FileDownloader {
+  FileDownloader();
+
+  final CancelToken _cancelToken = CancelToken();
+  bool _cancelled = false;
+
+  bool get isCancelled => _cancelled;
+
+  void cancel() {
+    if (_cancelled) return;
+    _cancelled = true;
+    _cancelToken.cancel('user cancelled');
+  }
+
+  /// Kicks off the download. Returns immediately; the download progresses in
+  /// the background and events are delivered via callbacks. Callbacks are not
+  /// invoked once [cancel] has been called.
+  void run({
+    required Dio client,
+    required String url,
+    required String savePath,
+    required void Function(double percent) onProgress,
+    required void Function() onDone,
+    required void Function(Object error) onError,
+  }) {
+    client.download(
+      url,
+      savePath,
+      cancelToken: _cancelToken,
+      onReceiveProgress: (received, total) {
+        if (_cancelled || total <= 0) return;
+        onProgress((received / total) * 100);
+      },
+    ).then((_) {
+      if (_cancelled) return;
+      onDone();
+    }).catchError((Object error) {
+      if (_cancelled) return;
+      onError(error);
+    }).ignore();
+  }
+}