using System;

using System.Collections;

using System.Collections.Generic;

using System.Diagnostics.CodeAnalysis;

using System.Linq;

using Google.Protobuf;

​

public class Program

{

    public static void Main()

    {

        var tripEndRoundingError = TimeSpan.FromMinutes(1.5);

        var returnSet = new PendingBikeReturnRequestSet(tripEndRoundingError);

​

        var now = DateTimeOffset.UtcNow;

        var fiveMinutesAgo = now.AddMinutes(-5);

        var fiveSecondsAgo = now.AddSeconds(-5);

        var bikeOne = ByteString.CopyFromUtf8("01AB5D");

        var bikeTwo = ByteString.CopyFromUtf8("325C19");

​

        var bikeOneReturnNow = new KioskReturnRequest { DockNumber = 3, BikeRfidTag = bikeOne, TripEndTicks = now.ToUnixTimeMilliseconds() };

        var bikeOneReturnFiveMinutesAgo = new KioskReturnRequest { DockNumber = 3, BikeRfidTag = bikeOne, TripEndTicks = fiveMinutesAgo.ToUnixTimeMilliseconds() };

        var bikeOneReturnFiveSecondsAgo = new KioskReturnRequest { DockNumber = 3, BikeRfidTag = bikeOne, TripEndTicks = fiveSecondsAgo.ToUnixTimeMilliseconds() };

        var bikeTwoReturnFiveSecondsAgo = new KioskReturnRequest { DockNumber = 3, BikeRfidTag = bikeTwo, TripEndTicks = fiveSecondsAgo.ToUnixTimeMilliseconds() };

        returnSet.Add(bikeOneReturnNow);

        returnSet.Add(bikeOneReturnFiveMinutesAgo);

        returnSet.Add(bikeOneReturnFiveSecondsAgo);

        returnSet.Add(bikeTwoReturnFiveSecondsAgo);

        Console.WriteLine(string.Join($",{Environment.NewLine}", returnSet.Select(bikeReturn => bikeReturn.ToString())));

    }

}

​

public class KioskReturnRequest

{

    public int DockNumber { get; set; }

    public ByteString BikeRfidTag { get; set; }

    public long TripEndTicks { get; set; }

    public override string ToString() => $"{{ DockNumber: {DockNumber}, BikeRfidTag: {BikeRfidTag.ToStringUtf8()}, TripEnd: {DateTimeOffset.FromUnixTimeMilliseconds(TripEndTicks).UtcDateTime.ToString("mm:ss")} }}";

}

​

public static class DateTimeExtensions

{

    public static DateTime Round(this DateTime dateTime, TimeSpan roundBy)

    {

        long remainderTicks = dateTime.Ticks % roundBy.Ticks;

        if (remainderTicks < roundBy.Ticks / 2)

        {

            // round down

            return dateTime.AddTicks(-remainderTicks);

        }

​

        // round up

        return dateTime.AddTicks(roundBy.Ticks - remainderTicks);

    }

}

​

public class PendingBikeReturnRequestSet : IEnumerable<KioskReturnRequest>, ICollection<KioskReturnRequest>

{

    private readonly HashSet<KioskReturnRequest> _hashSet;

    public PendingBikeReturnRequestSet(TimeSpan tripEndDateRoundingError) => _hashSet = new HashSet<KioskReturnRequest>(

        new KioskReturnRequestEquality(tripEndDateRoundingError)

    );

​

    public IEnumerator<KioskReturnRequest> GetEnumerator() => _hashSet.GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => _hashSet.GetEnumerator();

    public int Count => _hashSet.Count;

    public void Add(KioskReturnRequest item) => _hashSet.Add(item); // duplicate values are ignored by hash set

    public void Clear() => _hashSet.Clear();

    public bool Contains(KioskReturnRequest item) => _hashSet.Contains(item);

    public void CopyTo(KioskReturnRequest[] array, int arrayIndex) => _hashSet.CopyTo(array, arrayIndex);

    public bool Remove(KioskReturnRequest item) => _hashSet.Remove(item);

    public bool IsReadOnly => false;

​

    private class KioskReturnRequestEquality : EqualityComparer<KioskReturnRequest>

    {

        private readonly TimeSpan _tripEndDateRoundingError;

​

        public KioskReturnRequestEquality(TimeSpan tripEndDateRoundingError) => _tripEndDateRoundingError = tripEndDateRoundingError;

​

        public override bool Equals([DisallowNull] KioskReturnRequest x, [DisallowNull] KioskReturnRequest y) =>

            x.DockNumber == y.DockNumber

            && string.Equals(x.BikeRfidTag?.ToStringUtf8(), y.BikeRfidTag?.ToStringUtf8(), StringComparison.OrdinalIgnoreCase)

            && RoundTripEnd(x).Equals(RoundTripEnd(y));

​

        public override int GetHashCode([DisallowNull] KioskReturnRequest returnRequest) => HashCode.Combine(

            returnRequest.DockNumber,

            returnRequest.BikeRfidTag?.ToStringUtf8().ToLower(),

            RoundTripEnd(returnRequest)

        );

​

        private DateTime RoundTripEnd(KioskReturnRequest returnRequest)

            => DateTimeOffset.FromUnixTimeMilliseconds(returnRequest.TripEndTicks)

                .UtcDateTime

                .Round(_tripEndDateRoundingError);

    }

}