using System;

using System.Collections.Generic;

using System.Collections.ObjectModel;

using System.Linq;

​

public class OrderItemCollection : Collection<OrderItem>

{

    public event EventHandler<OrderItemAddedEventArgs> OrderItemAdded = delegate { };

    public event EventHandler<OrderItemRemovedEventArgs> OrderItemRemoved = delegate { };

​

    public OrderItemCollection()

    {

    }

​

    public OrderItemCollection(IList<OrderItem> list) : base(list)

    {

        if(list == null)

        {

            throw new ArgumentNullException("value");

        }

        foreach(var item in list.ToList())

        {

            Items.Add(item);

        }

    }

​

    protected override void InsertItem(int index, OrderItem newItem)

    {

        base.InsertItem(index, newItem);

​

        if (OrderItemAdded != null)

        {

            OrderItemAdded.Invoke(this, new OrderItemAddedEventArgs(newItem));

        }

    }

​

    protected override void RemoveItem(int index)

    {

        OrderItem item = Items[index];

        base.RemoveItem(index);

​

        if (OrderItemAdded != null)

        {

            OrderItemRemoved.Invoke(this, new OrderItemRemovedEventArgs(item));

        }

    }

}

​

public class OrderItemAddedEventArgs : EventArgs

{

    public OrderItemAddedEventArgs(OrderItem item)

    {

        if (item == null)

        {

            throw new ArgumentNullException("item is null!");

        }

        else

        {

            OrderItem = item;

        }

    }

​

    public OrderItem OrderItem { get; private set; }

}

​

public class OrderItemRemovedEventArgs : EventArgs

{

    public OrderItemRemovedEventArgs(OrderItem item)

    {

        if (item == null)

        {

            throw new ArgumentNullException("item is null!");

        }

        else

        {

            OrderItem = item;

        }

    }

​

    public OrderItem OrderItem { get; private set; }

}

​

public class OrderItem

{

    public readonly int PartNumber;

    public readonly string Description;

    public readonly double UnitPrice;

    private int _quantity = 0;

​

    public OrderItem(int partNumber, string description, int quantity, double unitPrice)

    {

        this.PartNumber = partNumber;

        this.Description = description;

        this.Quantity = quantity;

        this.UnitPrice = unitPrice;

    }

​

    public int Quantity

    {

        get

        {

            return _quantity;

        }

        set

        {

            if (value < 0)

            {

                throw new ArgumentException("Quantity cannot be negative.");

            }

​

            _quantity = value;

        }

    }

​

    public override string ToString()

    {

        return String.Format("{0,9} {1,6} {2,-12} at {3,8:#,###.00} = {4,10:###,###.00}",

            PartNumber, _quantity, Description, UnitPrice, UnitPrice * _quantity);

    }

}

​

public class Order

{

    private readonly OrderItemCollection _orderItems;

​

    public OrderItemCollection OrderItems

    {

        get

        {

            return _orderItems;

        }

    }

​

    public Order(IList<OrderItem> orderItems)

    {

        if (orderItems == null)

        {

            throw new ArgumentNullException("value");

        }

​

        this._orderItems = new OrderItemCollection(orderItems);

        this._orderItems.OrderItemAdded += AddMessage;

        this._orderItems.OrderItemRemoved += RemovedMessage;

    }

​

    public void Add(OrderItem item)

    {

        _orderItems.Add(item);

    }

​

    public void Remove(int partNumber)

    {

        OrderItem itemForRemoving = _orderItems.First(item => item.PartNumber == partNumber);

        _orderItems.Remove(itemForRemoving);

    }

​

    private void AddMessage(object sender, OrderItemAddedEventArgs eventArgs)

    {

        Console.WriteLine("Item has added.");

    }

​

    private void RemovedMessage(object sender, OrderItemRemovedEventArgs eventArgs)

    {

        Console.WriteLine("Item has removed.");

    }

}

​

​

public class Program

{

    public static void Main()

    {

        var orderItems = new List<OrderItem>

            {

            new OrderItem(110072674, "Widget", 400, 45.17),

            new OrderItem(110072675, "Sprocket", 27, 5.3),

            new OrderItem(101030411, "Motor", 10, 237.5),

            new OrderItem(110072684, "Gear", 175, 5.17)

            };

​

        var order = new Order(orderItems);

        Display("Order #1", order);

​

        if (!order.OrderItems.Any(item => item.PartNumber == 111033401))

        {

            Console.WriteLine("Order #1 doesn't have #111033401 item.\n");

        }

​

        order.Add(new OrderItem(111033401, "Nut", 10, .5));

        order.Add(new OrderItem(127700026, "Crank", 27, 5.98));

        order.Remove(110072674);

​

        Display("Order #2", order);

​

        if (order.OrderItems.Any(item => item.PartNumber == 127700026))

        {

            Console.WriteLine("Order #2 has #127700026 item.");

        }

    }

​

    private static void Display(string title, Order order)

    {

        Console.WriteLine(title);

        foreach (OrderItem item in order.OrderItems)

        {

            Console.WriteLine(item);

        }

        Console.WriteLine();

    }

}