import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

import '../services/app_state.dart';
import '../services/cloud/cloud_storage_provider.dart';

enum _BrowseRoot { myFiles, sharedWithMe }

/// Lets the user navigate whichever cloud storage provider is connected —
/// their own files, and (if the provider supports it) files others have
/// shared with them — and pick a parent location. Confirming looks for (or
/// creates) the `Show Me The Fuel Refund` folder under that location, so
/// two people pointing at the same shared parent converge on the same app
/// folder, regardless of which provider each of them is using. Picking a
/// folder that's already named that directly (e.g. a shared folder set up
/// by someone else) uses it as-is instead of nesting another one inside —
/// see `CloudSyncService.selectAppFolder`.
class CloudFolderBrowserScreen extends StatefulWidget {
  const CloudFolderBrowserScreen({super.key});

  @override
  State<CloudFolderBrowserScreen> createState() => _CloudFolderBrowserScreenState();
}

class _CloudFolderBrowserScreenState extends State<CloudFolderBrowserScreen> {
  late final CloudStorageSession _session;

  _BrowseRoot _root = _BrowseRoot.myFiles;
  final List<CloudFolder> _pathStack = [];

  List<CloudFolder>? _folders;
  bool _loading = true;
  String? _error;
  bool _confirming = false;

  @override
  void initState() {
    super.initState();
    _session = context.read<AppState>().activeProvider!.beginSession();
    _load();
  }

  @override
  void dispose() {
    _session.close();
    super.dispose();
  }

  String get _rootLabel => _root == _BrowseRoot.myFiles ? 'My Files' : '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.myFiles) return 'root';
    return null;
  }

  /// The currently browsed-into folder's own name, so [_useThisFolder] can
  /// tell whether the user picked a folder already named
  /// `Show Me The Fuel Refund` — null at a virtual root ("My Files"),
  /// which is never itself named that.
  String? get _currentFolderName => _pathStack.isNotEmpty ? _pathStack.last.name : null;

  String get _breadcrumbPath =>
      ([_rootLabel] + _pathStack.map((f) => f.name).toList()).join(' / ');

  Future<void> _load() async {
    setState(() {
      _loading = true;
      _error = null;
    });

    try {
      List<CloudFolder> folders;
      if (_pathStack.isNotEmpty) {
        folders = await _session.listFolders(parentId: _pathStack.last.id);
      } else if (_root == _BrowseRoot.myFiles) {
        folders = await _session.listFolders(parentId: 'root');
      } else {
        folders = await _session.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(CloudFolder 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>().chooseCloudFolder(
            parentId: parentId,
            breadcrumbPath: _breadcrumbPath,
            currentFolderName: _currentFolderName,
          );
      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 providerName = context.read<AppState>().activeProvider!.displayName;
    final canUseCurrentFolder = _currentFolderId != null;

    return Scaffold(
      appBar: AppBar(title: Text('Choose $providerName Folder')),
      body: Column(
        children: [
          if (_session.supportsSharedWithMe)
            SegmentedButton<_BrowseRoot>(
              segments: const [
                ButtonSegment(value: _BrowseRoot.myFiles, label: Text('My Files')),
                ButtonSegment(value: _BrowseRoot.sharedWithMe, label: Text('Shared with me')),
              ],
              selected: {_root},
              onSelectionChanged: (selection) => _switchRoot(selection.first),
            ),
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
            child: SingleChildScrollView(
              scrollDirection: Axis.horizontal,
              child: Row(
                children: [
                  TextButton(
                    onPressed: () => _goToBreadcrumb(-1),
                    child: Text(_rootLabel),
                  ),
                  for (var i = 0; i < _pathStack.length; i++) ...[
                    const Icon(Icons.chevron_right, size: 18),
                    TextButton(
                      onPressed: () => _goToBreadcrumb(i),
                      child: Text(_pathStack[i].name),
                    ),
                  ],
                ],
              ),
            ),
          ),
          const Divider(height: 1),
          Expanded(child: _buildBody()),
        ],
      ),
      bottomNavigationBar: SafeArea(
        child: Padding(
          padding: const EdgeInsets.all(16),
          child: FilledButton.icon(
            onPressed: (!canUseCurrentFolder || _confirming) ? null : _useThisFolder,
            icon: _confirming
                ? const SizedBox(height: 16, width: 16, child: CircularProgressIndicator(strokeWidth: 2))
                : const Icon(Icons.check),
            label: Text('Use "$_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),
        );
      },
    );
  }
}