import 'package:drift/drift.dart';

import 'app_database.dart';

class InsufficientStockException implements Exception {
  const InsufficientStockException();

  @override
  String toString() => 'Not enough stock';
}

class ProductNotFoundException implements Exception {
  final String productId;

  const ProductNotFoundException(this.productId);

  @override
  String toString() => 'Product not found: $productId';
}

/// Atomic stock updates shared by the product and tab services, so they can
/// run inside either one's transaction.
extension StockQueries on AppDatabase {
  /// Products with infinite stock are only checked for existence.
  Future<void> decreaseStock(String productId, int amount) async {
    _validateStockAmount(amount);

    final updatedRows =
        await (update(products)..where(
              (row) =>
                  row.id.equals(productId) &
                  row.infiniteStock.not() &
                  row.stockQuantity.isBiggerOrEqualValue(amount),
            ))
            .write(
              ProductsCompanion.custom(
                stockQuantity: products.stockQuantity - Variable(amount),
              ),
            );

    if (updatedRows == 1) return;

    final product = await _findProduct(productId);
    if (!product.infiniteStock) throw const InsufficientStockException();
  }

  Future<void> increaseStock(String productId, int amount) async {
    _validateStockAmount(amount);

    final updatedRows =
        await (update(products)..where(
              (row) => row.id.equals(productId) & row.infiniteStock.not(),
            ))
            .write(
              ProductsCompanion.custom(
                stockQuantity: products.stockQuantity + Variable(amount),
              ),
            );

    if (updatedRows != 1) await _findProduct(productId);
  }

  Future<ProductRow> _findProduct(String productId) async {
    final product = await (select(
      products,
    )..where((row) => row.id.equals(productId))).getSingleOrNull();

    if (product == null) throw ProductNotFoundException(productId);

    return product;
  }

  void _validateStockAmount(int amount) {
    if (amount <= 0) {
      throw ArgumentError.value(amount, 'amount', 'Must be greater than zero');
    }
  }
}