using System;

​

public class Order

{

    private const int MaxItemsCount = 100;

    private readonly OrderItem[] orderItems = new OrderItem[Order.MaxItemsCount];

    private readonly OrderStatistics statistics = new OrderStatistics();

    public int ItemsCount { get; private set; } = 0;

    public decimal Total

    {

        get

        {

            decimal total = 0;

            for (int i = 0; i < this.ItemsCount; i++)

            {

                total += this.orderItems[i].Price * this.orderItems[i].Quantity;

            }

​

            return total;

        }

    }

​

    public void AddOrUpdateItem(string name, int quantity, decimal price = 0M)

    {

        if (this.ItemsCount < this.orderItems.Length - 1)

        {

            OrderItem newItem = new OrderItem

            {

                Name = name,

                Quantity = quantity,

                Price = price

            };

            OrderItem.OrderItemLookup alreadyOrderedResult = newItem.CheckIsAlreadyOrdered(this);

            if (!alreadyOrderedResult.IsAlreadyOrdered)

            {

                // new product, add it to array

                this.orderItems[this.ItemsCount] = newItem;

                this.statistics.UpdateStatistics(newItem);

                this.ItemsCount++;

                Console.WriteLine($"Adding new item '{name}' to order, with quantity={quantity} and price={price}");

            }

            else

            {

                // existing product, update its quantity

                OrderItem updatedItem = new OrderItem

                {

                    Name = this.orderItems[alreadyOrderedResult.Index].Name,

                    Quantity = this.orderItems[alreadyOrderedResult.Index].Quantity + quantity,

                    Price = this.orderItems[alreadyOrderedResult.Index].Price

                };

                this.orderItems[alreadyOrderedResult.Index] = updatedItem;

                this.statistics.UpdateStatistics(updatedItem);

                Console.WriteLine($"Updating item '{updatedItem.Name}' quantity to {updatedItem.Quantity} and keeping price={updatedItem.Price}");

            }

        }

        else

        {

            Console.WriteLine($"Cannot order more than {Order.MaxItemsCount} items");

        }

    }

​

    public void PrintOrder()

    {

        string noCrtHeading = "#".PadLeft(this.ItemsCount.ToString().Length, ' ');

        string itemNameHeading = "Item".PadRight(this.statistics.MaxItemNameCharacters + 5, ' ');

        string itemQuantityHeading = "Qty".PadLeft(this.statistics.MaxQuantityDigits + 5, ' ');

        string itemPriceHeading = "Price".PadLeft(this.statistics.MaxPriceDigits + 5, ' ');

        string itemTotalHeading = "Total".PadLeft(this.statistics.MaxItemTotalDigits + 5, ' ');

        string fullHeading = $"{noCrtHeading}  {itemNameHeading}{itemQuantityHeading}{itemPriceHeading}{itemTotalHeading}";

        Console.WriteLine(new string ('=', fullHeading.Length));

        Console.WriteLine(fullHeading);

        Console.WriteLine(new string ('-', fullHeading.Length));

        for (int i = 0; i < this.ItemsCount; i++)

        {

            string noCrt = (i + 1).ToString().PadLeft(this.ItemsCount.ToString().Length, ' ');

            string itemName = this.orderItems[i].Name.PadRight(this.statistics.MaxItemNameCharacters + 5, ' ');

            string itemQuantity = this.orderItems[i].Quantity.ToString().PadLeft(this.statistics.MaxQuantityDigits + 5, ' ');

            string itemPrice = this.orderItems[i].Price.ToString().PadLeft(this.statistics.MaxPriceDigits + 5, ' ');

            string itemTotal = this.orderItems[i].ItemTotal.ToString().PadLeft(this.statistics.MaxItemTotalDigits + 5, ' ');

            Console.WriteLine($"{noCrt}) {itemName}{itemQuantity}{itemPrice}{itemTotal}");

        }

​

        Console.WriteLine(new string ('-', fullHeading.Length));

        string grandTotalFooter = $"TOTAL = {this.Total.ToString().PadLeft(this.Total.ToString().Length + 5, ' ')}".PadLeft(fullHeading.Length, ' ');

        Console.WriteLine(grandTotalFooter);

        Console.WriteLine(new string ('=', fullHeading.Length));

    }

​

    private class OrderItem

    {

        public string Name { get; set; } = string.Empty;

        public int Quantity { get; set; } = 0;

        public decimal Price { get; set; } = 0M;

        public decimal ItemTotal { get { return this.Quantity * this.Price; } }

​

        public OrderItemLookup CheckIsAlreadyOrdered(Order o)

        {

            for (int i = 0; i < (o?.ItemsCount ?? 0); i++)

            {

                if (string.Equals(o?.orderItems?[i]?.Name, this.Name, StringComparison.OrdinalIgnoreCase))

                {

                    return new OrderItemLookup(true, i);

                }

            }

​

            return new OrderItemLookup(false, -1);

        }

​

        public class OrderItemLookup

        {

            public OrderItemLookup(bool isAlreadyOrdered, int index)

            {

                this.IsAlreadyOrdered = isAlreadyOrdered;

                this.Index = index;

            }

​

            public bool IsAlreadyOrdered

            {

                get;

            }

​

            public int Index

            {

                get;

            }

        }

    }

​

    private class OrderStatistics

    {

        public int MaxItemNameCharacters { get; set; } = 0;

        public int MaxQuantityDigits { get; set; } = 0;

        public int MaxPriceDigits { get; set; } = 0;

        public int MaxItemTotalDigits { get; set; } = 0;

        public void UpdateStatistics(OrderItem orderItem)

        {

            if (orderItem is null)

            {

                return;

            }

​

            if (orderItem.Name?.Length > this.MaxItemNameCharacters)

            {

                this.MaxItemNameCharacters = orderItem.Name?.Length ?? 0;

            }

​

            if (orderItem.Quantity.ToString().Length > this.MaxQuantityDigits)

            {

                this.MaxQuantityDigits = orderItem.Quantity.ToString().Length;

            }

​

            if (orderItem.Price.ToString().Length > this.MaxPriceDigits)

            {

                this.MaxPriceDigits = orderItem.Price.ToString().Length;

            }

​

            if (orderItem.ItemTotal.ToString().Length > this.MaxItemTotalDigits)

            {

                this.MaxItemTotalDigits = orderItem.ItemTotal.ToString().Length;

            }

        }

    }

}

​

public class Program

{

    public static void Main()

    {

        Order order = new Order();

        order.AddOrUpdateItem("Product 1", 1, 10);

        order.AddOrUpdateItem("Product 2", 2, 20);

        order.AddOrUpdateItem("Product 1", 2);

        order.PrintOrder();

    }

}