using System;
using System.Reactive;
using System.Reactive.Linq;
using System.Reactive.Subjects;

/// <summary>
/// Provides a timeout mechanism that will not timeout if it is signalled often enough
/// </summary>
internal class TrafficTimeout
{
    private readonly Action onTimeout;
    private object signalLock = new object();
    private IObserver<Unit> signals;

    /// <summary>
    /// Initialises a new instance of the <see cref="TrafficTimeout"/> class.
    /// </summary>
    /// <param name="timeout">The duration to wait after receiving signals before timing out.</param>
    /// <param name="onTimeout">The <see cref="Action"/> to perform when the the timeout duration expires.</param>
    public TrafficTimeout(TimeSpan timeout, Action onTimeout)
    {
        // Subscribe to a throttled observable to trigger the expirey
        var messageQueue = new BehaviorSubject<Unit>(Unit.Default);
        IDisposable subscription = null;
        subscription = messageQueue.Throttle(timeout).Subscribe(
        p =>
        {
            messageQueue.OnCompleted();
            messageQueue.Dispose();
        });

        this.signals = messageQueue.AsObserver();
        this.onTimeout = onTimeout;
    }

    /// <summary>
    /// Signals that traffic has been received.
    /// </summary>
    public void Signal()
    {
        lock (this.signalLock)
        {
            this.signals.OnNext(Unit.Default);
        }
    }
}