Added Google Drive storage location

lib/screens/drive_folder_browser_screen.dart

@@ -0,0 +1,219 @@
+import 'package:flutter/material.dart';
+import 'package:http/http.dart' as http;
+import 'package:provider/provider.dart';
+
+import '../services/app_state.dart';
+import '../services/drive_service.dart';
+
+enum _BrowseRoot { myDrive, sharedWithMe }
+
+/// Lets the user navigate their Google Drive — either "My Drive" or
+/// folders others have shared with them — and pick a parent location.
+/// Confirming looks for (or creates) the `MO-Fuel-Tax-Back` folder under
+/// that location, so two people pointing at the same shared parent
+/// converge on the same app folder.
+class DriveFolderBrowserScreen extends StatefulWidget {
+  const DriveFolderBrowserScreen({super.key});
+
+  @override
+  State<DriveFolderBrowserScreen> createState() => _DriveFolderBrowserScreenState();
+}
+
+class _DriveFolderBrowserScreenState extends State<DriveFolderBrowserScreen> {
+  late final http.Client _client;
+  late final DriveService _drive;
+
+  _BrowseRoot _root = _BrowseRoot.myDrive;
+  final List<DriveFolder> _pathStack = [];
+
+  List<DriveFolder>? _folders;
+  bool _loading = true;
+  String? _error;
+  bool _confirming = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _client = context.read<AppState>().driveAuth.authenticatedHttpClient();
+    _drive = DriveService(_client);
+    _load();
+  }
+
+  @override
+  void dispose() {
+    _client.close();
+    super.dispose();
+  }
+
+  String get _rootLabel => _root == _BrowseRoot.myDrive ? 'My Drive' : 'Shared with me';
+
+  /// The folder ID that "Use This Folder" would act on, or null if the
+  /// current view is a virtual listing (top-level "Shared with me") rather
+  /// than an actual folder.
+  String? get _currentFolderId {
+    if (_pathStack.isNotEmpty) return _pathStack.last.id;
+    if (_root == _BrowseRoot.myDrive) return 'root';
+    return null;
+  }
+
+  String get _breadcrumbPath =>
+      ([_rootLabel] + _pathStack.map((f) => f.name).toList()).join(' / ');
+
+  Future<void> _load() async {
+    setState(() {
+      _loading = true;
+      _error = null;
+    });
+
+    try {
+      List<DriveFolder> folders;
+      if (_pathStack.isNotEmpty) {
+        folders = await _drive.listFolders(parentId: _pathStack.last.id);
+      } else if (_root == _BrowseRoot.myDrive) {
+        folders = await _drive.listFolders(parentId: 'root');
+      } else {
+        folders = await _drive.listFolders(sharedWithMe: true);
+      }
+      if (!mounted) return;
+      setState(() {
+        _folders = folders;
+        _loading = false;
+      });
+    } catch (e) {
+      if (!mounted) return;
+      setState(() {
+        _error = 'Could not load folders: $e';
+        _loading = false;
+      });
+    }
+  }
+
+  void _switchRoot(_BrowseRoot root) {
+    if (root == _root) return;
+    setState(() {
+      _root = root;
+      _pathStack.clear();
+    });
+    _load();
+  }
+
+  void _openFolder(DriveFolder folder) {
+    setState(() => _pathStack.add(folder));
+    _load();
+  }
+
+  void _goToBreadcrumb(int index) {
+    // index == -1 means the root label itself.
+    setState(() {
+      if (index < 0) {
+        _pathStack.clear();
+      } else {
+        _pathStack.removeRange(index + 1, _pathStack.length);
+      }
+    });
+    _load();
+  }
+
+  Future<void> _useThisFolder() async {
+    final parentId = _currentFolderId;
+    if (parentId == null) return;
+
+    setState(() => _confirming = true);
+    try {
+      await context.read<AppState>().chooseDriveFolder(
+            parentId: parentId,
+            breadcrumbPath: _breadcrumbPath,
+          );
+      if (mounted) Navigator.of(context).pop();
+    } catch (e) {
+      if (mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(content: Text('Could not use this folder: $e')),
+        );
+      }
+    } finally {
+      if (mounted) setState(() => _confirming = false);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final canUseCurrentFolder = _currentFolderId != null;
+
+    return Scaffold(
+      appBar: AppBar(title: const Text('Choose Drive Folder')),
+      body: Column(
+        children: [
+          SegmentedButton<_BrowseRoot>(
+            segments: const [
+              ButtonSegment(value: _BrowseRoot.myDrive, label: Text('My Drive')),
+              ButtonSegment(value: _BrowseRoot.sharedWithMe, label: Text('Shared with me')),
+            ],
+            selected: {_root},
+            onSelectionChanged: (selection) => _switchRoot(selection.first),
+          ),
+          Padding(
+            padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
+            child: SingleChildScrollView(
+              scrollDirection: Axis.horizontal,
+              child: Row(
+                children: [
+                  TextButton(
+                    onPressed: () => _goToBreadcrumb(-1),
+                    child: Text(_rootLabel),
+                  ),
+                  for (var i = 0; i < _pathStack.length; i++) ...[
+                    const Icon(Icons.chevron_right, size: 18),
+                    TextButton(
+                      onPressed: () => _goToBreadcrumb(i),
+                      child: Text(_pathStack[i].name),
+                    ),
+                  ],
+                ],
+              ),
+            ),
+          ),
+          const Divider(height: 1),
+          Expanded(child: _buildBody()),
+        ],
+      ),
+      bottomNavigationBar: SafeArea(
+        child: Padding(
+          padding: const EdgeInsets.all(16),
+          child: FilledButton.icon(
+            onPressed: (!canUseCurrentFolder || _confirming) ? null : _useThisFolder,
+            icon: _confirming
+                ? const SizedBox(height: 16, width: 16, child: CircularProgressIndicator(strokeWidth: 2))
+                : const Icon(Icons.check),
+            label: Text('Use "$_breadcrumbPath"'),
+          ),
+        ),
+      ),
+    );
+  }
+
+  Widget _buildBody() {
+    if (_loading) {
+      return const Center(child: CircularProgressIndicator());
+    }
+    if (_error != null) {
+      return Center(child: Padding(padding: const EdgeInsets.all(24), child: Text(_error!)));
+    }
+    final folders = _folders ?? [];
+    if (folders.isEmpty) {
+      return const Center(child: Text('No folders here.'));
+    }
+    return ListView.builder(
+      itemCount: folders.length,
+      itemBuilder: (context, index) {
+        final folder = folders[index];
+        return ListTile(
+          leading: const Icon(Icons.folder_outlined),
+          title: Text(folder.name),
+          trailing: const Icon(Icons.chevron_right),
+          onTap: () => _openFolder(folder),
+        );
+      },
+    );
+  }
+}