using System;

​

var startDateTime = new DateTimeOffset( 2021, 01, 01, 00, 00, 00, TimeSpan.Zero );

var endDateTime = startDateTime.AddMinutes( 1 );

​

var clock = new FakeClock { UtcNow = new DateTimeOffset( 2021, 01, 01, 00, 00, 00, TimeSpan.Zero ) };

var foo = new Foo( clock, TimeSpan.FromMilliseconds( 500 ) )

{

    ActualSpeed = 60,

};

foo.Start();

​

while ( clock.UtcNow < endDateTime )

{

    var timeSpan = TimeSpan.FromMilliseconds( 500 + Random.Shared.Next( 5, 50 ) );

    clock.UtcNow += timeSpan;

    var slices = foo.Tick();

    Console.WriteLine( "[{0:hh:mm:ss.ffffff}] {1} ({2})", clock.UtcNow, foo.Distance, slices );

}

​

foo.Stop();

​

​

interface ISystemClock

{

    DateTimeOffset UtcNow { get; }

}

​

class RealTimeClock : ISystemClock

{

    public DateTimeOffset UtcNow => DateTimeOffset.UtcNow;

}

​

class FakeClock : ISystemClock

{

    public DateTimeOffset UtcNow { get; set; } = DateTimeOffset.UtcNow;

}

​

class Foo

{

    private DateTimeOffset _lastTick;

    public Foo( ISystemClock systemClock, TimeSpan slice )

    {

        SystemClock = systemClock;

        Slice = slice;

    }

    public bool IsRunning { get; private set; }

    public double ActualSpeed { get; set; }

    public double Distance { get; private set; }

    public ISystemClock SystemClock { get; }

    public TimeSpan Slice { get; }

    public int Tick()

    {

        if ( !IsRunning ) return 0;

        var now = SystemClock.UtcNow;

        var duration = now - _lastTick;

        if (duration < Slice) return 0;

        var slices = Convert.ToInt32( duration.TotalMilliseconds / Slice.TotalMilliseconds );

        var consumedDuration = slices * Slice;

        _lastTick = now - ( duration - consumedDuration );

​

        Distance += ActualSpeed / TimeSpan.FromMinutes( 1 ).TotalMilliseconds * slices * Slice.TotalMilliseconds;

        return slices;

    }

​

    public void Start()

    {

        if ( IsRunning ) return;

        _lastTick = SystemClock.UtcNow;

        IsRunning = true;

    }

    public void Stop()

    {

        if ( !IsRunning ) return;

​

        IsRunning = false;

    }

}

​