// Add a new class which implements IFlightFilter. 

// The purpose of this class is to filter out any flights that have ANY segment with an arrival date BEFORE the departure date

​

using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Flight Builder");

        var allFlights = new FlightBuilder().GetFlights();

        IFlightFilter filterList= new FilterFlights();

        var lst = filterList.Filter(allFlights);

        foreach(var item in lst){

        Console.WriteLine()

        }

        //Continue coding here (feel free to add new classes if you would prefer)

    }

    public class FilterFlights : IFlightFilter

    {

        public IList<Flight> Filter(IList<Flight> flights)

        {

            //return flights.Where(x=>x.Segments.Any(s=>s.ArrivalDate < s.DepartureDate)).ToList();

            return flights.Where(x=>x.Segments.Any(s=>s.ArrivalDate >= s.DepartureDate)).ToList();

        }

    }

    //Keep all of the below code unchanged

    public interface IFlightFilter

    {

        IList<Flight> Filter(IList<Flight> flights);

    }

    public class Flight

    {

        public int Id { get; set; }

        // Segments represent the different legs in a flight.  A direct flight will have only 1 segment. A flight from London Heathrow to New York JFK changing at Paris would have 2 segments as follows.

        // Segment 1: London (LHR) - Paris (CDG)

        // Segment 2: Paris (CDG) - New York (JFK)

        public IList<Segment> Segments { get; set; }

        public override string ToString() => $"Id: {Id}, Segments: {string.Join(", ", Segments.Select(s => s.ToString()))}";

    }

    // A Segment represents a part of a flight journey, for now we are only storing the departure date and arrival date.

    public class Segment

    {

        public DateTime DepartureDate { get; set; }

        public DateTime ArrivalDate { get; set; }

        public override string ToString() => $"DepartureDate: {DepartureDate}, ArrivalDate: {ArrivalDate}";

    }

    // This is a mock datasource class to produce some sample flight data.  Some of the data it produces is intentionally invalid.

    public sealed class FlightBuilder

    {

        public IList<Flight> GetFlights()

        {

            var threeDaysFromNow = DateTime.Now.AddDays(3);

​

            return new List<Flight>

            {

                // A normal flight with two hour duration

                CreateFlight(1, threeDaysFromNow, threeDaysFromNow.AddHours(2)),

​

                // A normal multi-segment flight

                CreateFlight(2, threeDaysFromNow, threeDaysFromNow.AddHours(2), threeDaysFromNow.AddHours(3), threeDaysFromNow.AddHours(5)),

                // A flight departing in the past

                CreateFlight(3, threeDaysFromNow.AddDays(-6), threeDaysFromNow),

​

                // A flight that departs before it arrives

                CreateFlight(4, threeDaysFromNow, threeDaysFromNow.AddHours(-6)),

​

                // A flight with more than two hours ground time

                CreateFlight(5, threeDaysFromNow, threeDaysFromNow.AddHours(2), threeDaysFromNow.AddHours(5), threeDaysFromNow.AddHours(6)),

​

                // Another flight with more than two hours ground time

                CreateFlight(6, threeDaysFromNow, threeDaysFromNow.AddHours(2), threeDaysFromNow.AddHours(3), threeDaysFromNow.AddHours(4), threeDaysFromNow.AddHours(6), threeDaysFromNow.AddHours(7))

            };

        }

​

        private static Flight CreateFlight(int id, params DateTime[] dates)

        {

            if (dates.Length % 2 != 0) 

                throw new ArgumentException("You must pass an even number of dates,", "dates");

​

            var departureDates = dates.Where((date, index) => index % 2 == 0);

            var arrivalDates = dates.Where((date, index) => index % 2 == 1);

​

            var segments = departureDates

                .Zip(arrivalDates, (departureDate, arrivalDate) => new Segment { DepartureDate = departureDate, ArrivalDate = arrivalDate })

                .ToList();

​

            return new Flight

            {

                Id = id,

                Segments = segments

            };

        }

    }

}