using System;

using System.Collections.Generic; 

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

}

​

public class ICustomer

{

    int customerId {get; set;}  

    string customerName {get; set;}

    string CustomerEmail {get; set;}

    List<Project> projects {get; set;}

}

​

​

public class Customer : ICustomer

{

    int customerId {get; set;}  

    string customerName {get; set;}

    string CustomerEmail {get; set;}

    List<Project> projects {get; set;}

}

​

public abstract class Project

{

    int projectId { get; set; }

    int customerId {get; set;}  

    string projectName { get;set;}

    public abstract float getBilling();

}

​

public class TimeBasedProject : Project

{

    int totalHrs { get; set; }

    float ratePerHrs { get; set; }

    public override float getBilling() {

        //calculate monthly bill and return

        return 0;

    }

}

​

public class MilestoneBasedProject : Project

{

    int projectId { get; set; }

    Milestone _miletone { get; set; }

    public override float getBilling() {

        //calculate monthly bill and return

        return 0;

    }

}

​

public class Milestone 

{

    int milestoneId { get; set; }

    int projectId { get; set; }

    bool isCompleted { get; set;}

    DateTime MileStoneCompletionDate {get;set;}

    float rate { get; set; }

}

​

public class Invoice

{

    int projectId { get; set; }

    int customerId { get; set; }

    bool IsEmailSent { get; set; }

    DateTime InvoiceSentDate { get; set; }

    Email email { get; set; }

    float finalAmt { get; set; }

    Invoice(Email _email) //inject dependancy

    {   email=_email; }

    void CreateInvoice()

    {

        //Monthly Invoice calculation Logic and set finalAmt for Invoice        

        //IsEmailSent=email.SendMail();

    }

}

​

public class Email

{

    string emailFrom  { get; set; }

    string emailTo  { get; set; }

    string emailBody  { get; set; }

    public bool SendMail(string emailFrom,string emailTo,string emailBody)

    {

        try{

            return true;

        }

        catch(Exception e)

        {

            return false;

        }

    }

}

​

public class Transaction

{

    int TransId { get; set; }

    string transType { get; set; }

    DateTime transDate { get; set; }

    float transAmt { get; set; }

    public List<Transaction> getTransByMonth(DateTime dt)

    {

        // Return list of transt for the provided Month

        return new List<Transaction>();

    }

}

​

​

public class InvoiceValidation

{

    List<Transaction> LstTrans { get; set; }

    List<Invoice> LstInvoice { get; set; }

    List<ICustomer> LstCust { get; set; }

    public void MapInvoice()

    {

        // Logic for mapping invoices with monthly transactions and Dispaying it as List

    }

}

​

​

​

​

​

​

​