support setting new download path on android

lib/foundation/local.dart

@@ -5,6 +5,7 @@ import 'package:path_provider/path_provider.dart';
 import 'package:sqlite3/sqlite3.dart';
 import 'package:venera/foundation/comic_source/comic_source.dart';
 import 'package:venera/foundation/comic_type.dart';
+import 'package:venera/foundation/log.dart';
 import 'package:venera/network/download.dart';
 import 'package:venera/pages/reader/reader.dart';
 import 'package:venera/utils/ext.dart';
@@ -158,12 +159,13 @@ class LocalManager with ChangeNotifier {
       return "Directory is not empty";
     }
     try {
-      await copyDirectory(
+      await copyDirectoryIsolate(
         Directory(path),
         newDir,
       );
       await File(FilePath.join(App.dataPath, 'local_path')).writeAsString(path);
-    } catch (e) {
+    } catch (e, s) {
+      Log.error("IO", e, s);
       return e.toString();
     }
     await Directory(path).deleteIgnoreError(recursive:true);

lib/pages/settings/app.dart

@@ -32,12 +32,28 @@ class _AppSettingsState extends State<AppSettings> {
           title: "Set New Storage Path".tl,
           actionTitle: "Set".tl,
           callback: () async {
-            var result;
+            String? result;
             if (App.isAndroid) {
-              context.showMessage(message: "Not supported".tl);
-              return;
-            }
-            else if (App.isIOS) {
+              var channel = const MethodChannel("venera/storage");
+              var permission = await channel.invokeMethod('');
+              if(permission != true) {
+                context.showMessage(message: "Permission denied".tl);
+                return;
+              }
+              var path = await selectDirectory();
+              if(path != null) {
+                // check if the path is writable
+                var testFile = File(FilePath.join(path, "test"));
+                try {
+                  await testFile.writeAsBytes([1]);
+                  await testFile.delete();
+                } catch (e) {
+                  context.showMessage(message: "Permission denied".tl);
+                  return;
+                }
+                result = path;
+              }
+            } else if (App.isIOS) {
               result = await selectDirectoryIOS();
             } else {
               result = await selectDirectory();

lib/pages/settings/settings_page.dart

@@ -4,6 +4,7 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_reorderable_grid_view/widgets/reorderable_builder.dart';
+import 'package:permission_handler/permission_handler.dart';
 import 'package:url_launcher/url_launcher_string.dart';
 import 'package:venera/components/components.dart';
 import 'package:venera/foundation/app.dart';

lib/utils/io.dart

@@ -1,5 +1,6 @@
 import 'dart:convert';
 import 'dart:io';
+import 'dart:isolate';
 
 import 'package:flutter/services.dart';
 import 'package:flutter_file_dialog/flutter_file_dialog.dart';
@@ -113,6 +114,12 @@ Future<void> copyDirectory(Directory source, Directory destination) async {
   }
 }
 
+Future<void> copyDirectoryIsolate(Directory source, Directory destination) async {
+  await Isolate.run(() {
+    copyDirectory(source, destination);
+  });
+}
+
 String findValidDirectoryName(String path, String directory) {
   var name = sanitizeFileName(directory);
   var dir = Directory("$path/$name");