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

class SyncOutbox {
  static const String _outboxStorageKey = 'motorsignal_sync_outbox_manifest_v1';
  static const int maxOutboxCapacity = 500;
  final SharedPreferences _prefs;
  final Map<String, SyncItem> _items = {};
  Future<void> _saveChain = Future<void>.value();
  bool _isLoaded = false;

  SyncOutbox(this._prefs) { load(); }
  bool get isLoaded => _isLoaded;
  int get count => _items.length;

  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) throw const FormatException('Outbox manifest is not a list');
      for (final entry in decoded) {
        try {
          final map = entry is Map<String, dynamic> ? entry : Map<String, dynamic>.from(entry as Map);
          final item = SyncItem.fromJson(map);
          // An app/process death cannot leave an upload genuinely in progress.
          // Requeue it so the provider can safely retry its deterministic operation.
          _items[item.key] = item.status == SyncStatus.uploading
              ? item.copyWith(status: SyncStatus.queued, clearNextRetry: true)
              : item;
        } catch (itemError) { debugPrint('[SyncOutbox] Skipped malformed item: $itemError'); }
      }
    } catch (e) { debugPrint('[SyncOutbox] Corrupt manifest recovered safely: $e'); _items.clear(); }
    _isLoaded = true;
  }

  Future<bool> _save() {
    final operation = _saveChain.then((_) async {
      if (_items.length > maxOutboxCapacity) {
        final terminal = _items.values.where((i) => i.status.isTerminal).toList()..sort((a, b) => a.createdAt.compareTo(b.createdAt));
        while (_items.length > maxOutboxCapacity && terminal.isNotEmpty) {
          _items.remove(terminal.removeAt(0).key);
        }
      }
      if (_items.length > maxOutboxCapacity) throw StateError('Sync outbox capacity reached with no evictable terminal items.');
      return _prefs.setString(_outboxStorageKey, jsonEncode(_items.values.map((e) => e.toJson()).toList()));
    });
    _saveChain = operation.then((_) {}, onError: (_) {});
    return operation;
  }

  SyncItem? getItem(int localRideId, String providerId) => _items['${providerId.trim()}:$localRideId'];
  List<SyncItem> getAllItems() => _items.values.toList(growable: false);
  List<SyncItem> getPendingItems() => _items.values.where((i) => i.status.isPending).toList(growable: false);
  List<SyncItem> getEligibleItems(DateTime now) => _items.values.where((i) => i.isEligibleForAttempt(now)).toList(growable: false);

  Future<SyncItem> enqueue(int localRideId, String providerId, {DateTime? now}) async {
    if (localRideId <= 0 || providerId.trim().isEmpty) throw ArgumentError('A positive localRideId and non-empty providerId are required.');
    final normalizedProvider = providerId.trim();
    final key = '$normalizedProvider:$localRideId';
    final existing = _items[key];
    if (existing != null) {
      if (existing.status == SyncStatus.synced || existing.status == SyncStatus.queued || existing.status == SyncStatus.uploading) return existing;
      final rearmed = existing.copyWith(status: SyncStatus.queued, clearLastError: true, clearNextRetry: true);
      _items[key] = rearmed; await _save(); return rearmed;
    }
    if (_items.length >= maxOutboxCapacity && !_items.values.any((i) => i.status.isTerminal)) throw StateError('Sync outbox capacity reached; pending rides were not discarded.');
    final item = SyncItem(localRideId: localRideId, providerId: normalizedProvider, status: SyncStatus.queued, createdAt: now ?? DateTime.now());
    _items[key] = item; await _save(); return item;
  }

  Future<void> update(SyncItem item) async { _items[item.key] = item; await _save(); }
  Future<void> remove(int localRideId, String providerId) async { if (_items.remove('${providerId.trim()}:$localRideId') != null) await _save(); }
  Future<void> clear() async { _items.clear(); _saveChain = Future<void>.value(); await _prefs.remove(_outboxStorageKey); }
  bool isRideSynced(int localRideId, String providerId) => getItem(localRideId, providerId)?.status == SyncStatus.synced;
}