namespace ConsoleApp2
{
    using System;
    using System.Threading;

    public class RpsExecuter
    {
        private System.Timers.Timer Timer { get; }

        private int _tokensLeft;

        private readonly int _maxTokens;

        public RpsExecuter(int maxRequests, TimeSpan perInterval)
        {
            if (maxRequests < 1)
            {
                throw new ArgumentException(nameof(maxRequests));
            }
            if (perInterval.TotalMilliseconds < 1)
            {
                throw new ArgumentException(nameof(perInterval));
            }

            _maxTokens = maxRequests;
            _tokensLeft = maxRequests;

            var msPeriod = perInterval.TotalMilliseconds / maxRequests;
            Timer = new System.Timers.Timer(msPeriod);
            Timer.Elapsed += (o, e) => TryPutToken();
            Timer.Start();
        }

        private void TryPutToken()
        {
            var tokens = Interlocked.Increment(ref _tokensLeft);
            if (tokens > _maxTokens)
            {
                Interlocked.Decrement(ref _tokensLeft);
            }
        }

        private bool TryPullToken()
        {
            var permission = Interlocked.Decrement(ref _tokensLeft);
            if (permission >= 0)
                return true;
            Interlocked.Increment(ref _tokensLeft);
            return false;
        }

        public bool CanExecute()
        {
            return TryPullToken();
        }
    }
}