using System;

using System.Collections.Generic;

using System.Linq;

using System.Threading.Tasks;

​

public class Program

{

    private static List<SalesRecord> salesRecords = new();

    public static void Main()

    {

        var currentServiceProvider = "AWS";

        var accManager = GetAccountManager(currentServiceProvider);

        var rand = new Random();

        Console.WriteLine("Enter User ID:");

        var userId = Console.ReadLine();

        Console.WriteLine("Enter Password:");

        var password = Console.ReadLine();

        // ... Authenticate user ...

        if(true){

​

            for (var i = 0; i < 10000; i++)

            {

                var item = i < 4000 ? "A" : i < 8000 ? "B" : "C";

                salesRecords.Add(new SalesRecord(item));

            }

​

            // ... Propagate salesRecords with random quantities ...

            Parallel.ForEach(salesRecords, r => {

                r.Qty = rand.Next(101);

            });

​

            Console.WriteLine("Which item do you want to view? (A/B/C):");

            var chosenItem = Console.ReadLine();

            // ... Display items by filtering and sorting them in descending order with linq expression ...

            IEnumerable<SalesRecord> salesRecordQuery =

                from salesRecord in salesRecords

                orderby salesRecord.Qty descending

                where salesRecord.Item == chosenItem

                select salesRecord; 

            foreach(SalesRecord record in salesRecordQuery){

                Console.WriteLine("{0}, {1}", record.Item, record.Qty);

            }

        }

    }

​

    public static IAccountManager GetAccountManager(string serviceProvider)

    {

        switch(serviceProvider){

            case "AWS":

                return new AwsAuthent();

            case "AZURE":

                return new AzureAuthent();

            default:

                return null;

        }

    }

}

​

public class SalesRecord

{

    private int _qty;

    public string Item { get; set; }

​

    public int Qty { 

        get{ return _qty; }

        set{ _qty = value; } 

    }

​

    public SalesRecord(string item)

    {

        Item = item;

        _qty = 0;

    }

}

​

public interface IAccountManager

{

    public bool Authenticate(string userId, string password);

}

​

// ... Interface Implementations ...

​

public class AwsService

{

    public bool Authenticate(string userId, string password)

    {

        return userId == "aws" && password == "abc123";

    }

​

    public bool DeleteUser(string userId)

    {

        return true;

    }

}

​

public class AzureService

{

    public bool AuthUser(string userId, string password)

    {

        return userId == "azure" && password == "abc321";

    }

​

    public bool RemoveUser(string userId)

    {

        return true;

    }

}

​

public class AwsAuthent : IAccountManager

{

    private AwsService service = new AwsService();

    public bool Authenticate(string userId, string password)

    {

        return service.Authenticate(userId, password);

    }

}

​

public class AzureAuthent : IAccountManager

{

    private AzureService service = new AzureService();

    public bool Authenticate(string userId, string password)

    {

        return service.AuthUser(userId, password);

    }

}

​