using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{   

    //For individual orders

    public record Order(string Customer,int Items, decimal Cost);

​

    //**********************************************************************************************

    // QUESTION TWO

    //**********************************************************************************************

    // Over time the thresholds and number of discounts keeps changing. How can this be addressed so   

    // that we do not have to keep changing the implementation of this function? 

    // (Can be a mock implementation and/or pseudo code)

    //**********************************************************************************************

    static public decimal CalculateDiscount(Order order) =>

    order switch

    {

        {Items: > 10, Cost: > 1000.00m} => 0.10m,

        {Items: > 5, Cost: > 500.00m} => 0.05m,

        Order { Cost: > 250.00m } => 0.02m,

        null => throw new ArgumentNullException(nameof(order), "Can't calculate discount on null order"),

        var someObject => 0m,

    };

    public record Discount(int Items, decimal Cost, decimal DiscountPercentage);

​

    static IEnumerable<Discount> Discounts = new Discount[]

    {

        new Discount(10, 1000.00m, 0.10m),

        new Discount(5, 500.00m, 0.05m),

        new Discount(0, 250.00m, 0.02m),

        new Discount(0, 0.0m, 0.0m),

    };

​

    static public decimal CalulateDiscountFromLookup(Order order)

    {

        var discounts = Discounts.Where(d => order.Items > d.Items && order.Cost > d.Cost);

​

        if (discounts.Count() > 0)

            return discounts.Max(d => d.DiscountPercentage);

​

        return 0;

    }   

    //Random test data generator

    static IEnumerable<Order> InitTestData(Random r)

    {

        var customers = new String[] {"Cust1","Cust2","Cust3","Cust4"};

        return Enumerable.Range(1,12).Aggregate(new List<Order>()

                                         ,(a,x) =>

                                                {

                                            a.Add(new (customers[x % 4],r.Next(50)

                                                       , Convert.ToDecimal(3500*r.NextDouble())));

                                                      return a;});

    }

    //For totals

    public record OrderTotal (String Customer, Double OrderCount,decimal Total, decimal Discount);

    //**********************************************************************************************

    // QUESTION ONE

    //**********************************************************************************************

    // Implement the following function to return a single OrderTotal record for each Customer with:

    //  Number of orders, Total of all non-discounted orders, total amount with discounts applied   

    //**********************************************************************************************

    static IEnumerable<OrderTotal> CalcResults(IEnumerable<Order> orders)

    {

        return orders.GroupBy(o => o.Customer).Select(obc =>

        {

            decimal totalBeforeDiscount = obc.Sum(o => o.Cost);

            decimal totalAfterDiscount = obc.Sum(o => o.Cost * (1 - CalculateDiscount(o)));

​

            return new OrderTotal(obc.Key, obc.Count(), totalBeforeDiscount, totalAfterDiscount);

​

            #region alternate interpretation of requirements.

            // Separates discounted and non-discounted orders

            // decimal nonDiscountedOrdersCost = obc.Where(o => CalculateDiscount(o) == 0m).Sum(o => o.Cost);

            // decimal discountedOrdersCost = obc.Where(o => CalculateDiscount(o) != 0m).Sum(o => o.Cost * (1 - CalculateDiscount(o)));

            #endregion

        });

    }

    public static void Main()

    {

        var data = InitTestData(new Random()).ToList();

        foreach( var p in CalcResults(data))

            Console.WriteLine("Customer {0} Order Count {1} Total {2} Discount {3:#.##}"

                              ,p.Customer,p.OrderCount,p.Total,p.Discount);     

    }

}