///
/// Ratchet State Manager – Hive Persistence for Ratchet Chain State
///
/// Manages the lifecycle of [RatchetState] objects in a dedicated Hive box.
/// Each entry is keyed by ``'{channelUuid}_{senderIdentifier}'``.
///
/// Phase 2 of the Hydra Apocalypse Ratchet.
///
import 'package:hive_ce/hive.dart';
import 'package:letusmsg/data/ratchet_state_data.dart';
import 'package:letusmsg/utilz/Llog.dart';

/// Manages persistence of [RatchetState] objects in Hive.
///
/// Provides CRUD operations for ratchet states and channel-level cleanup.
/// The box is opened lazily on first access and remains open for the app
/// lifetime.
///
/// ## Key Format
/// ``'{channelUuid}_{senderIdentifier}'`` — deterministic from the
/// [RatchetState.hiveKey] property.
///
/// ## Usage
/// ```dart
/// final manager = RatchetStateManager();
/// await manager.open();
///
/// // Save after ratchet advance
/// await manager.save(state);
///
/// // Load for decrypt
/// final state = await manager.load('chan-uuid', 'sender-id');
/// ```
class RatchetStateManager {
  static const String boxName = 'ratchet_state';

  Box<RatchetState>? _box;

  /// Whether the Hive box is currently open.
  bool get isOpen => _box?.isOpen ?? false;

  /// Open the ratchet state Hive box.
  ///
  /// Safe to call multiple times — returns immediately if already open.
  Future<void> open() async {
    if (_box != null && _box!.isOpen) return;
    try {
      _box = await Hive.openBox<RatchetState>(boxName);
    } catch (ex) {
      Llog.log.e('[RatchetStateManager] Failed to open box: $ex');
      rethrow;
    }
  }

  /// Ensure the box is open, opening it if necessary.
  Future<Box<RatchetState>> _ensureBox() async {
    if (_box == null || !_box!.isOpen) {
      await open();
    }
    return _box!;
  }

  /// Load ratchet state for a specific channel + sender.
  ///
  /// Returns ``null`` if no state exists (channel not yet initialized with
  /// ratchet, or pre-Phase 2 channel).
  Future<RatchetState?> load(
    String channelUuid,
    String senderIdentifier,
  ) async {
    final box = await _ensureBox();
    final key = _buildKey(channelUuid, senderIdentifier);
    return box.get(key);
  }

  /// Save ratchet state after advancing the chain.
  ///
  /// Must be called after every send/receive operation to persist the
  /// updated chain keys and counters.
  Future<void> save(RatchetState state) async {
    final box = await _ensureBox();
    await box.put(state.hiveKey, state);
  }

  /// Delete ratchet state for a specific channel + sender.
  Future<void> delete(
    String channelUuid,
    String senderIdentifier,
  ) async {
    final box = await _ensureBox();
    final key = _buildKey(channelUuid, senderIdentifier);
    await box.delete(key);
  }

  /// Delete all ratchet states for a channel (all senders).
  ///
  /// Called when a channel is deleted or left.  Iterates all keys in the box
  /// and removes those matching the channel prefix.
  Future<void> deleteChannel(String channelUuid) async {
    final box = await _ensureBox();
    final prefix = '${channelUuid}_';
    final keysToDelete = <dynamic>[];
    for (final key in box.keys) {
      if (key.toString().startsWith(prefix)) {
        keysToDelete.add(key);
      }
    }
    if (keysToDelete.isNotEmpty) {
      await box.deleteAll(keysToDelete);
      Llog.log.d('[RatchetStateManager] Deleted ${keysToDelete.length} '
          'ratchet state(s) for channel $channelUuid');
    }
  }

  /// List all ratchet states for a channel (all senders).
  ///
  /// Useful for debugging and testing.
  Future<List<RatchetState>> listForChannel(String channelUuid) async {
    final box = await _ensureBox();
    final prefix = '${channelUuid}_';
    final results = <RatchetState>[];
    for (final key in box.keys) {
      if (key.toString().startsWith(prefix)) {
        final state = box.get(key);
        if (state != null) results.add(state);
      }
    }
    return results;
  }

  /// Check if a ratchet state exists for a channel + sender.
  Future<bool> exists(
    String channelUuid,
    String senderIdentifier,
  ) async {
    final box = await _ensureBox();
    return box.containsKey(_buildKey(channelUuid, senderIdentifier));
  }

  /// Close the Hive box.
  ///
  /// Called during app shutdown or cleanup.
  Future<void> close() async {
    if (_box != null && _box!.isOpen) {
      await _box!.close();
    }
    _box = null;
  }

  /// Build the composite Hive key from channel + sender identifiers.
  static String _buildKey(String channelUuid, String senderIdentifier) {
    return '${channelUuid}_$senderIdentifier';
  }
}