import 'dart:convert';
import 'dart:typed_data';

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

import '../data/remote/spelling_words_remote_store.dart';
import '../theme/app_theme.dart';

/// Lists and manages canonical spelling words in the shared catalog.
class SpellingListScreen extends StatefulWidget {
  const SpellingListScreen({super.key});

  @override
  State<SpellingListScreen> createState() => _SpellingListScreenState();
}

class _SpellingListScreenState extends State<SpellingListScreen> {
  final SpellingWordsRemoteStore _api = SpellingWordsRemoteStore();

  List<String> _words = <String>[];
  bool _loading = true;
  String? _error;
  bool _busy = false;

  @override
  void initState() {
    super.initState();
    _load();
  }

  Future<void> _load() async {
    setState(() {
      _loading = true;
      _error = null;
    });
    try {
      final List<String> words = await _api.fetchWords();
      if (!mounted) {
        return;
      }
      setState(() {
        _words = words;
        _loading = false;
      });
    } catch (_) {
      if (!mounted) {
        return;
      }
      setState(() {
        _loading = false;
        _error = 'Could not load spelling words.';
      });
    }
  }

  Future<void> _runBusy(Future<void> Function() action) async {
    if (_busy) {
      return;
    }
    setState(() => _busy = true);
    try {
      await action();
    } finally {
      if (mounted) {
        setState(() => _busy = false);
      }
    }
  }

  Future<void> _onNew() async {
    final String? word = await showDialog<String>(
      context: context,
      builder: (BuildContext context) => const _NewWordDialog(),
    );
    if (word == null || word.trim().isEmpty) {
      return;
    }

    await _runBusy(() async {
      try {
        final List<String> words = await _api.addWord(word);
        if (!mounted) {
          return;
        }
        setState(() => _words = words);
        _showSnack('Added "${word.trim().toLowerCase()}"');
      } on SpellingWordsApiException catch (e) {
        if (e.statusCode == 409) {
          _showSnack('That word is already in the list.');
        } else {
          _showSnack('Could not add word.');
        }
      } catch (_) {
        _showSnack('Could not add word.');
      }
    });
  }

  Future<void> _onUpload() async {
    final FilePickerResult? result = await FilePicker.platform.pickFiles(
      type: FileType.custom,
      allowedExtensions: <String>['txt'],
      withData: true,
    );
    if (result == null || result.files.isEmpty) {
      return;
    }

    final PlatformFile file = result.files.first;
    final String? text = _readFileText(file);
    if (text == null || text.trim().isEmpty) {
      _showSnack('The file is empty or could not be read.');
      return;
    }

    await _runBusy(() async {
      try {
        final ({int added, int skipped}) stats = await _api.importText(text);
        await _load();
        if (!mounted) {
          return;
        }
        _showSnack('Upload complete: ${stats.added} added, ${stats.skipped} skipped');
      } catch (_) {
        _showSnack('Upload failed.');
      }
    });
  }

  Future<void> _onDownload() async {
    await _runBusy(() async {
      try {
        final String text = await _api.exportText();
        final Uint8List bytes = Uint8List.fromList(utf8.encode(text));
        final String? path = await FilePicker.platform.saveFile(
          dialogTitle: 'Save spelling words',
          fileName: 'spelling-words.txt',
          type: FileType.custom,
          allowedExtensions: <String>['txt'],
          bytes: bytes,
        );
        if (!mounted) {
          return;
        }
        if (path == null) {
          return;
        }
        _showSnack('Saved spelling word list');
      } catch (_) {
        _showSnack('Download failed.');
      }
    });
  }

  String? _readFileText(PlatformFile file) {
    final List<int>? bytes = file.bytes;
    if (bytes != null) {
      return utf8.decode(bytes);
    }
    return null;
  }

  void _showSnack(String message) {
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(content: Text(message)),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Spelling words'),
      ),
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: <Widget>[
          Padding(
            padding: const EdgeInsets.fromLTRB(16, 12, 16, 8),
            child: Wrap(
              spacing: 8,
              runSpacing: 8,
              children: <Widget>[
                FilledButton.icon(
                  key: const Key('spelling-words-new'),
                  onPressed: _busy ? null : _onNew,
                  icon: const Icon(Icons.add, size: 18),
                  label: const Text('New'),
                ),
                OutlinedButton.icon(
                  key: const Key('spelling-words-upload'),
                  onPressed: _busy ? null : _onUpload,
                  icon: const Icon(Icons.upload_file, size: 18),
                  label: const Text('Upload'),
                ),
                OutlinedButton.icon(
                  key: const Key('spelling-words-download'),
                  onPressed: _busy ? null : _onDownload,
                  icon: const Icon(Icons.download, size: 18),
                  label: const Text('Download'),
                ),
                if (_busy)
                  const Padding(
                    padding: EdgeInsets.all(8),
                    child: SizedBox(
                      width: 20,
                      height: 20,
                      child: CircularProgressIndicator(strokeWidth: 2),
                    ),
                  ),
              ],
            ),
          ),
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 16),
            child: Text(
              'One word per line in upload/download files. Download includes canonical words only (no quiz history).',
              style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                    color: AppColors.textSecondary,
                  ),
            ),
          ),
          const SizedBox(height: 8),
          Expanded(child: _buildBody()),
        ],
      ),
    );
  }

  Widget _buildBody() {
    if (_loading) {
      return const Center(
        child: CircularProgressIndicator(color: AppColors.accent),
      );
    }
    if (_error != null) {
      return Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            Text(_error!, style: const TextStyle(color: Colors.redAccent)),
            const SizedBox(height: 12),
            FilledButton(onPressed: _load, child: const Text('Retry')),
          ],
        ),
      );
    }
    if (_words.isEmpty) {
      return const Center(
        child: Text(
          'No spelling words yet. Add one or upload a text file.',
          style: TextStyle(color: AppColors.textSecondary),
        ),
      );
    }

    return RefreshIndicator(
      onRefresh: _load,
      color: AppColors.accent,
      child: ListView.separated(
        padding: const EdgeInsets.fromLTRB(16, 0, 16, 24),
        itemCount: _words.length,
        separatorBuilder: (_, __) => const Divider(height: 1),
        itemBuilder: (BuildContext context, int index) {
          final String word = _words[index];
          return ListTile(
            key: Key('spelling-word-$word'),
            title: Text(
              word,
              style: const TextStyle(
                color: AppColors.textPrimary,
                fontWeight: FontWeight.w500,
              ),
            ),
          );
        },
      ),
    );
  }
}

class _NewWordDialog extends StatefulWidget {
  const _NewWordDialog();

  @override
  State<_NewWordDialog> createState() => _NewWordDialogState();
}

class _NewWordDialogState extends State<_NewWordDialog> {
  final TextEditingController _controller = TextEditingController();

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return AlertDialog(
      title: const Text('New spelling word'),
      content: TextField(
        key: const Key('spelling-new-word-field'),
        controller: _controller,
        autofocus: true,
        decoration: const InputDecoration(
          hintText: 'Enter a word',
          border: OutlineInputBorder(),
        ),
        textInputAction: TextInputAction.done,
        onSubmitted: (_) => _submit(),
      ),
      actions: <Widget>[
        TextButton(
          onPressed: () => Navigator.of(context).pop(),
          child: const Text('Cancel'),
        ),
        FilledButton(
          key: const Key('spelling-new-word-add'),
          onPressed: _submit,
          child: const Text('Add'),
        ),
      ],
    );
  }

  void _submit() {
    final String word = _controller.text.trim();
    if (word.isEmpty) {
      return;
    }
    Navigator.of(context).pop(word);
  }
}