import 'dart:io';

import 'package:flutter/foundation.dart' show visibleForTesting;
import 'package:shared_preferences/shared_preferences.dart';

/// Records the user-picked vault root folder (an Obsidian-style vault) and
/// gates app startup behind a valid choice.
///
/// The vault root is the single folder under which all notebooks will live.
/// Phase 0 only persists the path and validates it exists; no data is moved
/// into the vault yet (later phases do that).
///
/// Persistence is SharedPreferences-backed under [vaultRootKey]. The service is
/// easily mockable: inject a [SharedPreferences] (e.g. from
/// `SharedPreferences.setMockInitialValues`) via the constructor for tests.
class VaultService {
  /// SharedPreferences key under which the vault root path is stored.
  static const String vaultRootKey = 'vaultRoot';

  final SharedPreferences _prefs;

  VaultService._(this._prefs);

  static VaultService? _instance;

  /// Singleton accessor, mirroring [DatabaseService.getInstance]. Lazily reads
  /// the shared [SharedPreferences] instance.
  static Future<VaultService> getInstance() async {
    if (_instance != null) return _instance!;
    final prefs = await SharedPreferences.getInstance();
    final service = VaultService._(prefs);
    _instance = service;
    return service;
  }

  /// Test-only constructor: inject a (typically mock) [SharedPreferences] so
  /// the vault root can be exercised without platform channels.
  @visibleForTesting
  VaultService.forTest(SharedPreferences prefs) : _prefs = prefs;

  /// Test-only: drop the cached singleton so the next [getInstance] rebuilds.
  @visibleForTesting
  static void resetForTest() {
    _instance = null;
  }

  /// The currently stored vault root path, or null if none has been chosen.
  String? get vaultRoot => _prefs.getString(vaultRootKey);

  /// Persist [path] as the vault root.
  Future<void> setVaultRoot(String path) async {
    await _prefs.setString(vaultRootKey, path);
  }

  /// Forget the stored vault root (e.g. to re-prompt the user).
  Future<void> clearVaultRoot() async {
    await _prefs.remove(vaultRootKey);
  }

  /// True iff a vault root is set AND that directory currently exists.
  ///
  /// Returns false when no path is stored or when the stored path no longer
  /// resolves to a directory (external drive unplugged, folder deleted) — the
  /// caller then re-prompts rather than silently scattering data elsewhere.
  Future<bool> vaultRootValid() async {
    final path = vaultRoot;
    if (path == null || path.isEmpty) return false;
    return Directory(path).exists();
  }
}