ActionBatcher.cs

public class ActionBatcher<T>
{
    private readonly Action<IReadOnlyList<T>> action;
    private List<T> batch;

    public ActionBatcher(Action<IReadOnlyList<T>> action)
    {
        this.action = action;
        batch = new List<T>();
    }

    public bool IsRunning { get; private set; }
    public IReadOnlyList<T> MostRecentBatch { get; private set; }
    public int BatchSize => batch.Count;

    public void RunOrBatch(T item)
    {
        batch.Add(item);
        if (!IsRunning)
        {
            IsRunning = true;
            RunNextBatch();
        }
    }

    public void RunNextBatch()
    {
        if (BatchSize > 0)
        {
            action(batch);
            MostRecentBatch = batch;
            batch = new List<T>();
        }
        else
        {
            IsRunning = false;
        }
    }
}