import 'dart:async';
import 'dart:io';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:path_provider/path_provider.dart';
import 'package:uuid/uuid.dart';

import '../data/note.dart';
import '../data/note_repository.dart';
import '../data/note_template.dart';
import '../sync/github_client.dart';
import '../sync/local_backup.dart';
import '../sync/sync_service.dart';
import '../sync/sync_settings.dart';
import 'note_editor.dart';
import 'notes_list_screen.dart';
import 'settings_screen.dart';

/// The landing screen: an always-focused text box for jotting an idea.
///
/// Per the product goal "no interruptions, immediate", text is persisted
/// to local storage on *every* keystroke. A note row is created lazily on
/// the first character typed, then updated in place. The explicit "Save"
/// action finalises the current idea and clears the field for the next
/// one (remote sync will hook in here later).
class CaptureScreen extends StatefulWidget {
  const CaptureScreen({
    required this.repository,
    this.httpClient,
    this.localBackup,
    super.key,
  });

  final NoteRepository repository;

  /// Injectable HTTP client for the sync path. Production leaves this null
  /// (the GitHubClient creates its own); tests pass a mock so the configured
  /// sync flow can be exercised without real network access.
  final http.Client? httpClient;

  /// Injectable local-disk backup. Production leaves this null (a platform
  /// file-backed instance is created); tests pass a fake with in-memory IO.
  final LocalBackup? localBackup;

  @override
  State<CaptureScreen> createState() => _CaptureScreenState();
}

class _CaptureScreenState extends State<CaptureScreen>
    with WidgetsBindingObserver {
  static const _uuid = Uuid();

  /// Single-flight guard so a launch sync and a background sync never overlap.
  bool _autoSyncing = false;

  /// Keeps an always-current Markdown backup on local disk and recovers from
  /// it on launch (third durability layer beside sync + Android Auto Backup).
  late final LocalBackup _localBackup;
  StreamSubscription<List<Note>>? _notesSub;

  /// Latest assembled text from the editor; persisted on change and re-saved
  /// when only priority/status change.
  String _draftText = '';

  /// Bumped on save to recreate the editor with a fresh, empty template.
  int _editorGeneration = 0;

  /// Id of the note currently being edited, or null before the first
  /// keystroke of a fresh draft.
  String? _draftId;
  DateTime? _draftCreatedAt;
  DateTime? _lastSavedAt;

  /// Priority/status applied to the current draft. Chosen before or during
  /// typing; persisted on the first keystroke and on every later change.
  Priority _draftPriority = Priority.defaultValue;
  Status _draftStatus = Status.todo;

  final SyncService _syncService = const SyncService();
  SyncSettings? _settings;
  bool _syncing = false;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    _localBackup = widget.localBackup ?? _platformLocalBackup();
    // Recover from the local backup first (covers an empty DB after a wipe),
    // then keep the backup current as notes change.
    _recoverFromBackup();
    _notesSub = widget.repository.watchNotes().listen(
      _localBackup.scheduleExport,
    );
    SyncSettings.load().then((s) {
      if (!mounted) return;
      setState(() => _settings = s);
      _autoSync(); // pull on launch so a reinstalled device recovers its notes
    });
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    _notesSub?.cancel();
    _localBackup.dispose();
    super.dispose();
  }

  /// Restores notes from the local backup file, but only into an empty DB so a
  /// stale backup never clobbers existing notes (merge-by-id stays safe too).
  Future<void> _recoverFromBackup() async {
    final existing = await widget.repository.listNotes();
    if (existing.isNotEmpty) return;
    final recovered = await _localBackup.recover();
    if (recovered.isNotEmpty) await widget.repository.importNotes(recovered);
  }

  // coverage:ignore-start
  // Platform file IO for the local backup: BACKLOG.md under ~/todo on desktop
  // (the path the user's workflow already reads), or the app documents dir on
  // mobile (which Android Auto Backup includes). Exercised by running the app;
  // tests inject an in-memory LocalBackup instead.
  static LocalBackup _platformLocalBackup() {
    Future<File> backupFile() async {
      if (Platform.isAndroid || Platform.isIOS) {
        final dir = await getApplicationDocumentsDirectory();
        return File('${dir.path}/todo-backlog.md');
      }
      final home = Platform.environment['HOME'] ?? Directory.current.path;
      final dir = Directory('$home/todo')..createSync(recursive: true);
      return File('${dir.path}/BACKLOG.md');
    }

    return LocalBackup(
      reader: () async {
        final file = await backupFile();
        return file.existsSync() ? file.readAsString() : null;
      },
      writer: (markdown) async => (await backupFile()).writeAsString(markdown),
    );
  }
  // coverage:ignore-end

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    // Push on background so the remote (the durable store) stays near-current.
    if (state == AppLifecycleState.paused) _autoSync();
  }

  /// Best-effort background sync: silent, skips when unconfigured, and never
  /// overlaps itself. Failures are swallowed — the manual Sync button is the
  /// place that surfaces errors.
  Future<void> _autoSync() async {
    final settings = _settings;
    if (_autoSyncing || settings == null || !settings.isConfigured) return;
    _autoSyncing = true;
    final client = GitHubClient(
      owner: settings.owner,
      repo: settings.repo,
      token: settings.token,
      httpClient: widget.httpClient,
    );
    try {
      await _syncService.sync(widget.repository, client);
    } catch (_) {
      // Best-effort: ignore (offline, transient GitHub errors, etc.).
    } finally {
      client.close();
      _autoSyncing = false;
    }
  }

  /// Opens the settings screen and adopts any saved configuration.
  Future<void> _openSettings() async {
    final current = _settings ?? await SyncSettings.load();
    if (!mounted) return;
    await Navigator.of(context).push<SyncSettings>(
      MaterialPageRoute(
        builder: (_) => SettingsScreen(
          initial: current,
          repository: widget.repository,
          httpClient: widget.httpClient,
        ),
      ),
    );
    if (!mounted) return;
    // Always reload from storage: a device-flow "Connect" saves the token
    // without popping a result, so relying on the pop value would miss it and
    // leave us syncing with stale (token-less) settings.
    final fresh = await SyncSettings.load();
    setState(() => _settings = fresh);
  }

  void _openList() {
    Navigator.of(context).push<void>(
      MaterialPageRoute(
        builder: (_) => NotesListScreen(repository: widget.repository),
      ),
    );
  }

  /// Runs a full sync, routing to settings first if not yet configured.
  Future<void> _sync() async {
    final settings = _settings ?? await SyncSettings.load();
    if (!settings.isConfigured) {
      _showSnack('Add a GitHub token in settings to enable sync');
      await _openSettings();
      return;
    }
    setState(() => _syncing = true);
    final client = GitHubClient(
      owner: settings.owner,
      repo: settings.repo,
      token: settings.token,
      httpClient: widget.httpClient,
    );
    try {
      final result = await _syncService.sync(widget.repository, client);
      _showSnack('Synced: merged ${result.mergedDevices} device(s)');
    } catch (e) {
      _showSnack('Sync failed: $e');
    } finally {
      client.close();
      if (mounted) setState(() => _syncing = false);
    }
  }

  void _showSnack(String message) {
    if (!mounted) return;
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(content: Text(message), duration: const Duration(seconds: 2)),
    );
  }

  /// Persists the current text on every change. Creates the note row on
  /// the first non-empty keystroke so empty drafts never hit storage.
  Future<void> _onChanged(String text) async {
    _draftText = text;
    if (_draftId == null) {
      // A note is only created once the user actually fills something in, so
      // an empty template (no section typed yet) never hits storage.
      if (text.trim().isEmpty) return;
      _draftId = _uuid.v4();
      _draftCreatedAt = DateTime.now();
    }
    final now = DateTime.now();
    await widget.repository.upsert(
      Note(
        id: _draftId!,
        text: text,
        priority: _draftPriority,
        status: _draftStatus,
        createdAt: _draftCreatedAt!,
        updatedAt: now,
      ),
    );
    if (mounted) setState(() => _lastSavedAt = now);
  }

  /// Applies a new priority to the draft, persisting immediately if a note
  /// row already exists (otherwise it is applied on the first keystroke).
  Future<void> _setPriority(Priority priority) async {
    setState(() => _draftPriority = priority);
    await _persistDraftMeta();
  }

  /// Applies a new status to the draft, persisting immediately if a note
  /// row already exists.
  Future<void> _setStatus(Status status) async {
    setState(() => _draftStatus = status);
    await _persistDraftMeta();
  }

  /// Re-saves the draft's metadata when only priority/status changed.
  Future<void> _persistDraftMeta() async {
    if (_draftId == null) return;
    final now = DateTime.now();
    await widget.repository.upsert(
      Note(
        id: _draftId!,
        text: _draftText,
        priority: _draftPriority,
        status: _draftStatus,
        createdAt: _draftCreatedAt!,
        updatedAt: now,
      ),
    );
    if (mounted) setState(() => _lastSavedAt = now);
  }

  /// Finalises the current idea and resets the field to a fresh template.
  void _saveAndReset() {
    // A note was actually persisted only if a draft row was created.
    final saved = _draftId != null;
    setState(() {
      _editorGeneration++; // recreate the editor with a fresh template
      _draftText = '';
      _draftId = null;
      _draftCreatedAt = null;
      _lastSavedAt = null;
      _draftPriority = Priority.defaultValue;
      _draftStatus = Status.todo;
    });
    if (saved) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(
          content: Text('Idea saved locally'),
          duration: Duration(seconds: 1),
        ),
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    return Scaffold(
      appBar: AppBar(
        title: const Text('Capture'),
        actions: [
          // Live count of stored notes, proving local persistence.
          StreamBuilder<int>(
            stream: widget.repository.watchCount(),
            builder: (context, snapshot) {
              final count = snapshot.data ?? 0;
              return Padding(
                padding: const EdgeInsets.only(right: 4),
                child: Center(child: Text('$count saved')),
              );
            },
          ),
          IconButton(
            tooltip: 'Sync',
            onPressed: _syncing ? null : _sync,
            icon: _syncing
                ? const SizedBox(
                    width: 18,
                    height: 18,
                    child: CircularProgressIndicator(strokeWidth: 2),
                  )
                : const Icon(Icons.sync),
          ),
          IconButton(
            tooltip: 'Notes',
            onPressed: _openList,
            icon: const Icon(Icons.list),
          ),
          IconButton(
            tooltip: 'Sync settings',
            onPressed: _openSettings,
            icon: const Icon(Icons.settings),
          ),
        ],
      ),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            // Pickers sit above the editor so the bottom-right Save FAB
            // never overlaps them.
            Row(
              children: [
                Expanded(
                  child: _MetaDropdown<Priority>(
                    label: 'Priority',
                    value: _draftPriority,
                    values: Priority.values,
                    labelOf: (p) => p.label,
                    onChanged: _setPriority,
                  ),
                ),
                const SizedBox(width: 12),
                Expanded(
                  child: _MetaDropdown<Status>(
                    label: 'Status',
                    value: _draftStatus,
                    values: Status.values,
                    labelOf: (s) => s.label,
                    onChanged: _setStatus,
                  ),
                ),
              ],
            ),
            const SizedBox(height: 12),
            Expanded(
              child: NoteEditor(
                key: ValueKey(_editorGeneration),
                initialTemplate: NoteTemplate.defaultTemplate,
                autofocus: true,
                onChanged: _onChanged,
              ),
            ),
            const SizedBox(height: 8),
            // Leave room so the Save FAB doesn't cover the save indicator.
            Padding(
              padding: const EdgeInsets.only(right: 96),
              child: Text(
                _lastSavedAt == null
                    ? 'Autosaves as you type'
                    : 'Saved locally at ${_formatTime(_lastSavedAt!)}',
                style: theme.textTheme.bodySmall,
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton.extended(
        onPressed: _saveAndReset,
        icon: const Icon(Icons.check),
        label: const Text('Save'),
      ),
    );
  }

  /// Formats a timestamp as zero-padded HH:mm:ss for the save indicator.
  String _formatTime(DateTime t) {
    String two(int n) => n.toString().padLeft(2, '0');
    return '${two(t.hour)}:${two(t.minute)}:${two(t.second)}';
  }
}

/// A compact labelled dropdown for picking an enum value (priority/status).
///
/// Generic over the enum type [T] so the same control drives both pickers
/// without duplication; [labelOf] maps a value to its display string.
class _MetaDropdown<T> extends StatelessWidget {
  const _MetaDropdown({
    required this.label,
    required this.value,
    required this.values,
    required this.labelOf,
    required this.onChanged,
  });

  final String label;
  final T value;
  final List<T> values;
  final String Function(T) labelOf;
  final ValueChanged<T> onChanged;

  @override
  Widget build(BuildContext context) {
    return InputDecorator(
      decoration: InputDecoration(
        labelText: label,
        isDense: true,
        border: const OutlineInputBorder(),
        contentPadding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
      ),
      child: DropdownButtonHideUnderline(
        child: DropdownButton<T>(
          value: value,
          isDense: true,
          isExpanded: true,
          items: [
            for (final v in values)
              DropdownMenuItem<T>(value: v, child: Text(labelOf(v))),
          ],
          onChanged: (v) {
            if (v != null) onChanged(v);
          },
        ),
      ),
    );
  }
}