using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;

namespace DTS.Common.Utils
{
    public class StopWatchQueue
    {
        private readonly Stopwatch _stopWatch;
        private readonly Queue<long> _watchQueue;
        private readonly string _name;

        public StopWatchQueue(string name)
        {
            _stopWatch = new Stopwatch();
            _watchQueue = new Queue<long>(5000);
            _name = name;
        }

        private static double CalculateStdDev(IEnumerable<double> values)
        {
            double ret = 0;

            var valuesArray = values as double[] ?? values.ToArray();
            if (valuesArray.Length <= 1) return ret;
            //Compute the Average
            var avg = valuesArray.Average();

            //Perform the Sum of (value-avg)^2
            var sum = valuesArray.Sum(d => Math.Pow(d - avg, 2));

            //Put it all together
            ret = Math.Sqrt(sum / (valuesArray.Length - 1));
            return ret;
        }

        ~StopWatchQueue()
        {
            DumpData();
        }

        public void DumpData()
        {
            if (_watchQueue.Count == 0)
                return;
            var qArray = new double[_watchQueue.Count];
            for (var idx = 0; idx < qArray.Length; idx++)
                qArray[idx] = Convert.ToDouble(_watchQueue.Dequeue()) / Stopwatch.Frequency * 1000D;
            var qMax = qArray.Max();
            var qMin = qArray.Min();
            var qAvg = qArray.Average();
            var qStd = CalculateStdDev(qArray);
            var fName = _name + DateTime.Now.ToFileTime() + ".csv";
            using (var sw = new StreamWriter(fName, false))
            {
                sw.WriteLine("The StopWatchQueue contains {0} entries", qArray.Length);
                sw.WriteLine("Max={0} Min={1} Average={2} StdDev={3}", qMax, qMin, qAvg, qStd);
                sw.WriteLine("All values in milli seconds");
                for (var idx = 0; idx < qArray.Length; idx++)
                    sw.WriteLine("{0},{1}", idx, qArray[idx]);
            }
        }

        public void Start()
        {
            _stopWatch.Start();
        }

        public void Stop()
        {
            _watchQueue.Enqueue(_stopWatch.ElapsedTicks);
            _stopWatch.Reset();
        }
    }
}