using System;
using System.Threading;

namespace Laservall.Solidworks.Server
{
    internal sealed class HeartbeatMonitor : IDisposable
    {
        private readonly TimeSpan _timeout;
        private readonly Action _onTimeout;
        private Timer _timer;
        private long _lastPingTicks;
        private bool _running;
        private bool _disposed;

        public HeartbeatMonitor(TimeSpan timeout, Action onTimeout)
        {
            _timeout = timeout;
            _onTimeout = onTimeout;
        }

        public void Start()
        {
            _lastPingTicks = DateTime.UtcNow.Ticks;
            _running = true;
            _timer = new Timer(CheckTimeout, null, _timeout, _timeout);
        }

        public void Stop()
        {
            _running = false;
            _timer?.Change(Timeout.Infinite, Timeout.Infinite);
        }

        public void Ping()
        {
            Interlocked.Exchange(ref _lastPingTicks, DateTime.UtcNow.Ticks);
        }

        private void CheckTimeout(object state)
        {
            if (!_running) return;

            long lastPing = Interlocked.Read(ref _lastPingTicks);
            var elapsed = TimeSpan.FromTicks(DateTime.UtcNow.Ticks - lastPing);

            if (elapsed > _timeout)
            {
                _running = false;
                _onTimeout?.Invoke();
            }
        }

        public void Dispose()
        {
            if (_disposed) return;
            _disposed = true;
            _timer?.Dispose();
        }
    }
}