///////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2017, Carnegie Mellon University and University of Cambridge,
// all rights reserved.
//
// ACADEMIC OR NON-PROFIT ORGANIZATION NONCOMMERCIAL RESEARCH USE ONLY
//
// BY USING OR DOWNLOADING THE SOFTWARE, YOU ARE AGREEING TO THE TERMS OF THIS LICENSE AGREEMENT.  
// IF YOU DO NOT AGREE WITH THESE TERMS, YOU MAY NOT USE OR DOWNLOAD THE SOFTWARE.
//
// License can be found in OpenFace-license.txt

//     * Any publications arising from the use of this software, including but
//       not limited to academic journal and conference publications, technical
//       reports and manuals, must cite at least one of the following works:
//
//       OpenFace: an open source facial behavior analysis toolkit
//       Tadas Baltrušaitis, Peter Robinson, and Louis-Philippe Morency
//       in IEEE Winter Conference on Applications of Computer Vision, 2016  
//
//       Rendering of Eyes for Eye-Shape Registration and Gaze Estimation
//       Erroll Wood, Tadas Baltrušaitis, Xucong Zhang, Yusuke Sugano, Peter Robinson, and Andreas Bulling 
//       in IEEE International. Conference on Computer Vision (ICCV),  2015 
//
//       Cross-dataset learning and person-speci?c normalisation for automatic Action Unit detection
//       Tadas Baltrušaitis, Marwa Mahmoud, and Peter Robinson 
//       in Facial Expression Recognition and Analysis Challenge, 
//       IEEE International Conference on Automatic Face and Gesture Recognition, 2015 
//
//       Constrained Local Neural Fields for robust facial landmark detection in the wild.
//       Tadas Baltrušaitis, Peter Robinson, and Louis-Philippe Morency. 
//       in IEEE Int. Conference on Computer Vision Workshops, 300 Faces in-the-Wild Challenge, 2013.    
//
///////////////////////////////////////////////////////////////////////////////

using System;
using System.Collections.Generic;

namespace OpenFaceOffline
{
    public class FpsTracker
    {
        public TimeSpan HistoryLength { get; set; }
        public FpsTracker()
        {
            HistoryLength = TimeSpan.FromSeconds(2);
        }

        private Queue<DateTime> frameTimes = new Queue<DateTime>();

        private void DiscardOldFrames()
        {
            while (frameTimes.Count > 0 && (MainWindow.CurrentTime - frameTimes.Peek()) > HistoryLength)
                frameTimes.Dequeue();
        }

        public void AddFrame()
        {
            frameTimes.Enqueue(MainWindow.CurrentTime);
            DiscardOldFrames();
        }

        public double GetFPS()
        {
            DiscardOldFrames();

            if (frameTimes.Count == 0)
                return 0;

            return frameTimes.Count / (MainWindow.CurrentTime - frameTimes.Peek()).TotalSeconds;
        }
    }
}