import '../../domain/entities/customer.dart';
import '../../domain/entities/product.dart';
import '../../domain/entities/sync_event.dart';
import '../local/app_database.dart';
import '../local/catalogue_dao.dart';
import '../local/order_dao.dart';
import '../local/promo_dao.dart';
import '../local/staff_dao.dart';
import '../local/sync_config_store.dart';
import '../local/sync_log_dao.dart';
import '../local/terminal_identity.dart';

/// Terminal-side storage facade.
///
/// SQLite is the source of truth. The catalogue is additionally held in memory
/// because barcode resolution happens on every scan and the product grid reads
/// it constantly — but every write goes to disk first, so nothing depends on
/// the process staying alive.
class LocalStore {
  LocalStore._();

  static final LocalStore instance = LocalStore._();

  late CatalogueDao catalogue;
  late OrderDao orders;
  late SyncLogDao syncLog;
  late StaffDao staff;
  late PromoDao promos;
  late SyncConfigStore syncConfig;
  late TerminalIdentityStore identityStore;

  /// Who this till is. Minted on first run, then stable forever.
  late TerminalIdentity terminal;

  final Map<String, Product> _products = {};
  final Map<String, Customer> _customers = {};
  final List<SyncEvent> _syncEvents = [];

  DateTime? _lastImportAt;
  String? _catalogueRevision;
  int _unsyncedOrders = 0;

  bool _ready = false;

  bool get isReady => _ready;

  /// Opens the database and loads the catalogue into memory.
  Future<void> init({String? databasePath, bool inMemory = false}) async {
    if (inMemory) {
      await AppDatabase.instance.openInMemory();
    } else {
      await AppDatabase.instance.open(overridePath: databasePath);
    }

    catalogue = CatalogueDao(AppDatabase.instance.db);
    orders = OrderDao(AppDatabase.instance.db);
    syncLog = SyncLogDao(AppDatabase.instance.db);
    staff = StaffDao(AppDatabase.instance.db);
    promos = PromoDao(AppDatabase.instance.db);
    syncConfig = SyncConfigStore(catalogue);
    identityStore = TerminalIdentityStore(catalogue);

    // A terminal with no staff cannot be signed into at all, so this runs
    // before anything else can ask who is on shift.
    await staff.seedIfEmpty();

    // Before anything can be written or published: a bill stamped with the
    // wrong terminal cannot be traced back to the till that rang it.
    terminal = await identityStore.load();

    await hydrate();
    _ready = true;
  }

  /// Re-reads cached state from disk. Called on start and after an import.
  Future<void> hydrate() async {
    _products
      ..clear()
      ..addEntries(
        (await catalogue.allProducts()).map((p) => MapEntry(p.id, p)),
      );
    _customers
      ..clear()
      ..addEntries(
        (await catalogue.allCustomers()).map((c) => MapEntry(c.id, c)),
      );

    final stamp = await catalogue.meta(MetaKeys.lastImportAt);
    _lastImportAt = stamp == null
        ? null
        : DateTime.fromMillisecondsSinceEpoch(int.parse(stamp));
    _catalogueRevision = await catalogue.meta(MetaKeys.catalogueRevision);
    terminal = await identityStore.load();
    _unsyncedOrders = await orders.unsyncedCount();

    _syncEvents
      ..clear()
      ..addAll(await syncLog.recent());
  }

  // ---------------------------------------------------------------- Sync log
  /// Newest first. Backed by the table, so it survives a restart.
  List<SyncEvent> get syncEvents => List.unmodifiable(_syncEvents);

  Future<void> appendSyncEvent(SyncEvent event) async {
    await syncLog.insert(event);
    await syncLog.trim();
    _syncEvents.insert(0, event);
  }

  /// Test helper: wipes every table and reloads.
  Future<void> reset({bool withCatalogue = false}) async {
    if (!_ready) await init(inMemory: true);
    await AppDatabase.instance.clear();

    // Staff and identity are cleared with everything else, and a terminal
    // without them cannot be signed into or stamp a bill. Re-minted here so a
    // reset leaves a usable till rather than a half-built one.
    await staff.seedIfEmpty();
    terminal = await identityStore.load();

    if (withCatalogue) {
      // Imported here rather than at the top of the file so the seed data is
      // only pulled in by tests and the simulated remote source.
      await catalogue.replaceCatalogue(
        products: _seedProducts(),
        customers: _seedCustomers(),
      );
      await catalogue.setMeta(
        MetaKeys.lastImportAt,
        '${DateTime.now().millisecondsSinceEpoch}',
      );
      await catalogue.setMeta(MetaKeys.catalogueRevision, 'seed');
    }

    await hydrate();
  }

  // -------------------------------------------------------------- Catalogue
  /// True once products exist on this terminal. Billing is gated on it.
  bool get hasCatalogue => _products.isNotEmpty;

  DateTime? get lastImportAt => _lastImportAt;
  String? get catalogueRevision => _catalogueRevision;
  int get unsyncedOrders => _unsyncedOrders;

  Future<void> importCatalogue({
    required List<Product> products,
    required List<Customer> customers,
    required String revision,
    required DateTime at,
    bool isDelta = false,
    List<String> retiredProductIds = const [],
  }) async {
    if (isDelta) {
      // A change set must not withdraw what it does not mention. Applied as a
      // full snapshot, the first morning price change would empty the shelf.
      await catalogue.applyCatalogueDelta(
        products: products,
        customers: customers,
        retiredProductIds: retiredProductIds,
      );
    } else {
      await catalogue.replaceCatalogue(
        products: products,
        customers: customers,
      );
    }

    // The server's stock figure predates any sale this terminal has made but
    // not yet uploaded, so those units would reappear on the shelf. Replay them
    // before anyone can bill against the inflated count.
    //
    // Scoped to the products the pull actually overwrote. A full snapshot
    // rewrites every row, so the replay covers everything; a delta rewrites
    // only what it carried, and replaying the rest would subtract those units a
    // second time from a count that was never reset — quietly emptying a shelf
    // that is full.
    var committed = await orders.unsyncedStockCommitments();
    if (isDelta) {
      final touched = products.map((p) => p.id).toSet();
      committed = {
        for (final entry in committed.entries)
          if (touched.contains(entry.key)) entry.key: entry.value,
      };
    }
    if (committed.isNotEmpty) {
      await catalogue.decrementStock(committed);
    }

    await catalogue.setMeta(
      MetaKeys.lastImportAt,
      '${at.millisecondsSinceEpoch}',
    );
    await catalogue.setMeta(MetaKeys.catalogueRevision, revision);
    await hydrate();
  }

  // --------------------------------------------------------------- Products
  List<Product> get products => _products.values.toList(growable: false);

  Product? productById(String id) => _products[id];

  Product? productByBarcode(String barcode) {
    final needle = barcode.trim();
    for (final p in _products.values) {
      if (p.barcode == needle && p.isActive) return p;
    }
    return null;
  }

  /// Write-through: disk first, then the cache.
  Future<void> putProduct(Product p) async {
    await catalogue.upsertProduct(p);
    _products[p.id] = p;
  }

  Future<void> applyStockMovement(Map<String, double> quantities) async {
    await catalogue.decrementStock(quantities);
    cacheStockMovement(quantities);
  }

  /// Mirrors a stock decrement already written to disk into the memory cache.
  /// Used after a sale is committed as part of a larger transaction.
  void cacheStockMovement(Map<String, double> quantities) {
    quantities.forEach((id, qty) {
      final p = _products[id];
      if (p == null) return;
      _products[id] =
          p.copyWith(stock: (p.stock - qty).clamp(0, double.infinity));
    });
  }

  // -------------------------------------------------------------- Customers
  List<Customer> get customers => _customers.values.toList(growable: false);

  Customer? customerById(String id) => _customers[id];

  Future<void> putCustomer(Customer c) async {
    await catalogue.upsertCustomer(c);
    _customers[c.id] = c;
  }

  /// Mirrors a customer already written to disk into the memory cache.
  void cacheCustomer(Customer c) => _customers[c.id] = c;

  // ----------------------------------------------------------------- Orders
  /// Refreshes the cached unsynced tally after a write or a sync.
  Future<int> refreshUnsyncedCount() async {
    _unsyncedOrders = await orders.unsyncedCount();
    return _unsyncedOrders;
  }

  // ------------------------------------------------------------- Seed data
  // Kept behind these hooks so production code never reaches for them.
  static List<Product> Function() _seedProducts = () => const [];
  static List<Customer> Function() _seedCustomers = () => const [];

  /// Lets the simulated remote source and tests supply demo rows.
  static void registerSeed({
    required List<Product> Function() products,
    required List<Customer> Function() customers,
  }) {
    _seedProducts = products;
    _seedCustomers = customers;
  }
}