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using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace ConsolePlayground
{
    unsafe delegate void UnsafeOperation(short* samples, int size);

    class Program
    {
        // depth is fixed 16 bit (short)
        private const int SampleRate = 44100;

        private const int ChannelCount = 2;
        private static readonly TimeSpan UpdateInterval = TimeSpan.FromMilliseconds(10);

        private static readonly TimeSpan Duration = TimeSpan.FromSeconds(10);


        private static readonly Random Random = new Random();

        static void Main(string[] args)
        {
            Trace.Listeners.Clear();

            var twtl = new TextWriterTraceListener("../../Data/Log.txt")
            {
                Name = "TextLogger",
            };

            var ctl = new ConsoleTraceListener(false);

            Trace.Listeners.Add(twtl);
            Trace.Listeners.Add(ctl);
            Trace.AutoFlush = true;
            
            Task.Run(Run).Wait();
        }

        static async Task Run()
        {
            Trace.WriteLine($"================== Benchmark Begin ==================");
#if DEBUG
            Trace.WriteLine($"Mode:            {(Environment.Is64BitProcess ? "x64" : "x32")} Debug {(Debugger.IsAttached ? "+ Debugger" : "")}");
#else
            Trace.WriteLine($"Mode:            {(Environment.Is64BitProcess ? "x64" : "x32")} Release {(Debugger.IsAttached ? "+ Debugger" : "")}");
#endif

            Trace.WriteLine($"Sample Rate:     {SampleRate}Hz");
            Trace.WriteLine($"Channel Count:   {ChannelCount}");
            Trace.WriteLine($"Update Interval: {UpdateInterval.TotalMilliseconds}ms");
            Trace.WriteLine("");

            var sampleCount = (int) (UpdateInterval.TotalSeconds * SampleRate * sizeof(short) * ChannelCount);


            Trace.WriteLine($"Testing \"{nameof(ConvertUsingBitConverter)}\" for {Duration.TotalSeconds:f3}s...");

            var generator = GenerateSamples(sampleCount);
            var totalWatch = Stopwatch.StartNew();
            var watch = new Stopwatch();
            var records = new List<TimeSpan>((int) (Duration.Ticks / UpdateInterval.Ticks));

            while (totalWatch.Elapsed < Duration)
            {
                watch.Restart();
                var buffer = await generator;
                generator = GenerateSamples(sampleCount);

                var samples = ConvertUsingBitConverter(buffer);
                DoSomething(samples);
                watch.Stop();

                records.Add(watch.Elapsed);
            }

            PrintResults(totalWatch.Elapsed, records);


            Trace.WriteLine($"Testing \"{nameof(ConvertUsingMarshaling)}\" for {Duration.TotalSeconds:f3}s...");

            generator = GenerateSamples(sampleCount);
            totalWatch = Stopwatch.StartNew();
            records.Clear();

            while (totalWatch.Elapsed < Duration)
            {
                watch.Restart();
                var buffer = await generator;
                generator = GenerateSamples(sampleCount);

                var samples = ConvertUsingMarshaling(buffer);
                DoSomething(samples);
                watch.Stop();

                records.Add(watch.Elapsed);
            }

            PrintResults(totalWatch.Elapsed, records);


            Trace.WriteLine($"Testing \"{nameof(ConvertUsingUnsafeCode)}\" for {Duration.TotalSeconds:f3}s...");

            generator = GenerateSamples(sampleCount);
            totalWatch = Stopwatch.StartNew();
            records.Clear();


            while (totalWatch.Elapsed < Duration)
            {
                watch.Restart();
                var buffer = await generator;
                generator = GenerateSamples(sampleCount);

                unsafe
                {
                    ConvertUsingUnsafeCode(buffer, DoSomething);
                }

                watch.Stop();

                records.Add(watch.Elapsed);
            }

            PrintResults(totalWatch.Elapsed, records);

            Trace.WriteLine($"================== Benchmark End ==================");
            Trace.WriteLine("");

            if (Debugger.IsAttached)
            {
                Console.WriteLine("Press any key to exit...");
                Console.ReadKey(false);
            }
        }

        static void PrintResults(TimeSpan totalTime, List<TimeSpan> records)
        {
            Trace.WriteLine($"Actual Duration:  {totalTime.TotalMilliseconds,6:#}ms");
            Trace.WriteLine($"Max allowed time: {UpdateInterval.TotalMilliseconds * 1000,6:#}µs");
            Trace.WriteLine($"Mean time:        {records.Average(r => r.TotalMilliseconds) * 1000,6:#}µs");
            Trace.WriteLine($"Median time:      {records.OrderBy(r => r).ElementAt(records.Count / 2).TotalMilliseconds * 1000,6:#}µs");
            Trace.WriteLine(
                $"Min time:         {records.Min().TotalMilliseconds * 1000,6:#}µs at iteration {records.IndexOf(records.Min())}");
            Trace.WriteLine(
                $"Max time:         {records.Max().TotalMilliseconds * 1000,6:#}µs at iteration {records.IndexOf(records.Max())}");
            Trace.WriteLine($"Iterations:       {records.Count,6}");
            Trace.WriteLine($"Over performance: {records.Count / (Duration.Ticks / UpdateInterval.Ticks) * 100,6:#}%");
            Trace.WriteLine("");
        }

        static void DoSomething(short[] samples)
        {
            unchecked
            {
                for (int i = 1; i < samples.Length - 1; i++)
                {
                    samples[i] = (short) (samples[i - 1] ^ samples[i + 1]);
                    samples[i] *= (short) (samples[i] + 1220);
                    samples[i] <<= i % 4;
                    samples[i] >>= i % 3;
                }
            }
        }

        static unsafe void DoSomething(short* samples, int size)
        {
            unchecked
            {
                for (int i = 1; i < size - 1; i++)
                {
                    samples[i] = (short) (samples[i - 1] ^ samples[i + 1]);
                    samples[i] *= (short) (samples[i] + 1220);
                    samples[i] <<= i % 4;
                    samples[i] >>= i % 3;
                }
            }
        }

        static async Task<byte[]> GenerateSamples(int count)
        {
            return await Task.Run(() =>
            {
                var buffer = new byte[count];
                Random.NextBytes(buffer);
                return buffer;
            });
        }

        static short[] ConvertUsingBitConverter(byte[] buffer)
        {
            var result = new short[buffer.Length / sizeof(short)];

            for (int i = 0; i < result.Length; i++)
                result[i] = BitConverter.ToInt16(buffer, i * sizeof(short));

            return result;
        }

        static short[] ConvertUsingMarshaling(byte[] buffer)
        {
            var result = new short[buffer.Length / sizeof(short)];

            var pinnedArray = GCHandle.Alloc(buffer, GCHandleType.Pinned);
            var pointer = pinnedArray.AddrOfPinnedObject();
            Marshal.Copy(pointer, result, 0, result.Length);
            pinnedArray.Free();

            return result;
        }
        
        static unsafe void ConvertUsingUnsafeCode(byte[] buffer, UnsafeOperation operation)
        {
            fixed (byte* ptr = buffer)
            {
                operation((short*) ptr, buffer.Length / sizeof(short));
            }
        }
    }
}