using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Timers;

namespace TrackerBridge.DSP
{
    class GazeDecimator : IGazeFilter
    {
        public event GazeDataHandler OutputAvailable;

        private GazeData output;
        private Single outputFrequency;
        private Timer timer;
        private readonly Object outputLock = new Object();
        private readonly Object valueCountLock = new Object();
        private Int64 valueCount;

        private Int64 ValueCount {
            get {
                lock (valueCountLock)
                {
                    return valueCount;
                }
            }
            set {
                lock (valueCountLock)
                {
                    valueCount = value;
                }
            }
        }

        private GazeData Output {
            get {
                lock (outputLock)
                {
                    return output;
                }
            }
            set {
                lock (outputLock)
                {
                    output = value;
                }
            }
        }

        public GazeDecimator(GazeDataProcessor dataProcessor)
        {
            outputFrequency = dataProcessor.OutputFrequency;
            SetupTimer();
        }
        public void Input(GazeData input, Object sender = null)
        {
            if (ValueCount == 0)
            {
                Output = input;
            }
            else
            {
                //Cumulative moving average (CMA) -> https://en.wikipedia.org/wiki/Moving_average#Cumulative_moving_average
                lock (outputLock)
                {
                    output += (input - output) / (ValueCount + 1);
                }

            }
            ValueCount++;
        }

        public void Reset()
        {
            ValueCount = 0;
        }

        private void SetupTimer()
        {
            timer?.Stop();
            timer?.Dispose();
            timer = new Timer(1000.0 / outputFrequency);
            timer.Elapsed += (Object sender, ElapsedEventArgs e) =>
            {
                if (ValueCount > 0)
                {
                    OutputAvailable?.Invoke(Output, this);
                    Reset();
                }
            };
            timer.AutoReset = true;
            timer.Start();
        }

        public void Update(GazeDataProcessor dataProcessor)
        {
            outputFrequency = dataProcessor.OutputFrequency;
            SetupTimer();
        }
    }
}