import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'sync_models.dart';

/// Persistent, crash-resilient local synchronization outbox.
/// Operates outside Drift Schema 5, ensuring zero database schema changes or migrations.
class SyncOutbox {
  static const String _outboxStorageKey = 'motorsignal_sync_outbox_manifest_v1';
  static const int maxOutboxCapacity = 500;

  final SharedPreferences _prefs;
  final Map<String, SyncItem> _items = {};
  bool _isLoaded = false;

  SyncOutbox(this._prefs) {
    load();
  }

  bool get isLoaded => _isLoaded;
  int get count => _items.length;

  /// Loads and deserializes outbox items from persistent storage with corruption recovery
  void load() {
    _items.clear();
    final rawJson = _prefs.getString(_outboxStorageKey);
    if (rawJson == null || rawJson.trim().isEmpty) {
      _isLoaded = true;
      return;
    }

    try {
      final decoded = jsonDecode(rawJson);
      if (decoded is List) {
        for (final entry in decoded) {
          try {
            if (entry is Map<String, dynamic>) {
              final item = SyncItem.fromJson(entry);
              _items[item.key] = item;
            } else if (entry is Map) {
              final item = SyncItem.fromJson(Map<String, dynamic>.from(entry));
              _items[item.key] = item;
            }
          } catch (itemError) {
            debugPrint('[SyncOutbox] Skipped malformed item in outbox: $itemError');
          }
        }
      }
    } catch (e) {
      debugPrint('[SyncOutbox] Corruption detected in outbox manifest, resetting safely: $e');
      _items.clear();
    }

    _isLoaded = true;
  }

  /// Atomically writes current outbox manifest to persistent storage
  Future<bool> _save() async {
    try {
      // Bound outbox capacity to avoid unbounded memory / storage growth
      final list = _items.values.toList();
      if (list.length > maxOutboxCapacity) {
        list.sort((a, b) => a.createdAt.compareTo(b.createdAt));
        // Keep most recent items
        final trimmed = list.sublist(list.length - maxOutboxCapacity);
        _items.clear();
        for (final item in trimmed) {
          _items[item.key] = item;
        }
      }

      final encoded = jsonEncode(_items.values.map((e) => e.toJson()).toList());
      return await _prefs.setString(_outboxStorageKey, encoded);
    } catch (e) {
      debugPrint('[SyncOutbox] Error saving outbox manifest: $e');
      return false;
    }
  }

  /// Retrieves an item by its ride ID and provider ID
  SyncItem? getItem(int localRideId, String providerId) {
    final key = '${localRideId}_$providerId';
    return _items[key];
  }

  /// Returns all currently tracked items
  List<SyncItem> getAllItems() {
    return _items.values.toList(growable: false);
  }

  /// Returns all items requiring action or waiting for retry
  List<SyncItem> getPendingItems() {
    return _items.values.where((item) => item.status.isPending).toList(growable: false);
  }

  /// Returns all items currently eligible for an immediate upload attempt
  List<SyncItem> getEligibleItems(DateTime now) {
    return _items.values
        .where((item) => item.isEligibleForAttempt(now))
        .toList(growable: false);
  }

  /// Enqueues a local ride for a target provider.
  /// Deduplicates: if already queued or synced, returns existing item without duplicate insertion.
  Future<SyncItem> enqueue(
    int localRideId,
    String providerId, {
    DateTime? now,
  }) async {
    final key = '${localRideId}_$providerId';
    final existing = _items[key];

    if (existing != null) {
      if (existing.status == SyncStatus.synced) {
        return existing; // Already completed
      }
      if (existing.status == SyncStatus.queued || existing.status == SyncStatus.uploading) {
        return existing; // Already active in queue
      }
      // Re-arm failed or waiting item
      final rearmed = existing.copyWith(
        status: SyncStatus.queued,
        clearLastError: true,
        clearNextRetry: true,
      );
      _items[key] = rearmed;
      await _save();
      return rearmed;
    }

    final newItem = SyncItem(
      localRideId: localRideId,
      providerId: providerId,
      status: SyncStatus.queued,
      createdAt: now ?? DateTime.now(),
    );

    _items[key] = newItem;
    await _save();
    return newItem;
  }

  /// Updates the state of an existing outbox item
  Future<void> update(SyncItem item) async {
    _items[item.key] = item;
    await _save();
  }

  /// Removes an item from the outbox
  Future<void> remove(int localRideId, String providerId) async {
    final key = '${localRideId}_$providerId';
    if (_items.remove(key) != null) {
      await _save();
    }
  }

  /// Clears the entire outbox
  Future<void> clear() async {
    _items.clear();
    await _prefs.remove(_outboxStorageKey);
  }

  /// Checks if a ride is marked synced for the specified provider
  bool isRideSynced(int localRideId, String providerId) {
    final item = getItem(localRideId, providerId);
    return item?.status == SyncStatus.synced;
  }
}