// Copyright 2019 The Flutter team. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/foundation.dart';
import 'package:provider_shopper/models/catalog.dart';

class CartModel extends ChangeNotifier {
  /// The current catalog. Used to construct items from numeric ids.
  final CatalogModel _catalog;

  /// Internal, private state of the cart. Stores the ids of each item.
  final List<int> _itemIds;

  /// Construct a CartModel instance that is backed by a [CatalogModel] and
  /// an optional previous state of the cart.
  ///
  /// If [previous] is not `null`, its items are copied to the newly
  /// constructed instance.
  CartModel(this._catalog, CartModel previous)
      : assert(_catalog != null),
        _itemIds = previous?._itemIds ?? [];

  /// An empty cart with no Catalog.
  CartModel.empty()
      : _catalog = null,
        _itemIds = [];

  /// List of items in the cart.
  List<Item> get items => _itemIds.map((id) => _catalog.getById(id)).toList();

  /// The current total price of all items.
  int get totalPrice =>
      items.fold(0, (total, current) => total + current.price);

  /// Adds [item] to cart. This is the only way to modify the cart from outside.
  void add(Item item) {
    _itemIds.add(item.id);
    // This line tells [Model] that it should rebuild the widgets that
    // depend on it.
    notifyListeners();
  }
}