//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="MatrixParallel.cs"
// Project: StgSharp
// AuthorGroup: Nitload Space
// Copyright (c) Nitload Space. All rights reserved.
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using StgSharp.HighPerformance;
using StgSharp.HighPerformance.Memory;

using System;
using System.Collections.Generic;
using System.IO.Pipes;
using System.Linq;
using System.Reflection.Metadata;
using System.Runtime.CompilerServices;
using System.Runtime.ExceptionServices;
using System.Text;
using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;

namespace StgSharp.Mathematics
{
    /*
    * Thread wrapping to accelerate matrix operations by dividing threads into groups (wraps).
    * For M wraps, each containing an average of N threads, we satisfy the condition M * N = T - 4,
    * where T is the total thread count of the CPU. Typically, for modern consumer CPUs, T is around 16.
    * For simplicity, let M * N = 16.
    *
    * The total time complexity for publishing tasks is O(M + N):
    * - O(M) accounts for distributing tasks across M wraps.
    * - O(N) accounts for threads within each wrap fetching tasks from the wrap queue.
    *
    * Using the inequality Sqrt(M * N) <= (M + N) / 2 (derived from the arithmetic-geometric mean inequality),
    * the optimal configuration occurs when M = N. For M * N = 16, this gives M = N = 4.
    * 
    * To ensure compatibility across a wide range of CPU architectures, 
    * we allow each wrap to contain either 3 or 4 threads, providing flexibility while maintaining efficiency.
    */

    internal static class MatrixParallel
    {

        private static Thread[] _threads;
        private static MatrixParallelWrap[] _wraps;
        private static readonly (int a, int b)[] LookupTable =
        [(1, 1), (0, 2), (3, 0), (2, 1),
         (1, 2), (0, 3), (3, 1), (2, 2), (1, 3),
         (0, 4), (3, 2), (2, 3), (1, 4), (0, 5),];
        private static volatile int RemainThreadCount = 0;

        private static readonly ManualResetEventSlim _restartEvent = new(false);
        private static readonly ManualResetEventSlim _startEvent = new(false);

        private static MatrixParallelTaskPackage _totalTask;
        private static readonly object _lock = new();
        private static ThreadPriority _AfterWork = ThreadPriority.Lowest;

        public static ref MatrixParallelTaskPackage TotalTask => ref _totalTask;

        public static bool SupportParallel { get; } = Environment.ProcessorCount > 6;

        public static bool IsParallelMeaningful { get; } = Environment.ProcessorCount > 6;

        internal static MatrixParallelWrap.Handle LeaderHandle { get; private set; }

        public static void EndParallel()
        {
            Monitor.Exit(_lock);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static (int a, int b) FastDecompose(int c)
        {
            if (c < 7) {
                return (0, 0);
            }
            c -= 7;
            int c_prime = c / 14;
            int d = c % 14;

            (int a_prime, int b_prime) = LookupTable[d];

            return (a_prime + c_prime, b_prime + c_prime);
        }

        public static void Init()
        {
            int count = Environment.ProcessorCount - 4;
            count = count == 5 ? 4 : count;
            int _3wrap = 0, _4wrap = 0;
            _threads = new Thread[count];
            if (count < 6) { } else if (count == 6) { } else { }
            LeaderHandle = new MatrixParallelWrap.Handle(0, _wraps[0]);
        }

        public static void LaunchParallel(SleepMode afterWork)
        {
            _startEvent.Set();
            _restartEvent.Reset();
            RemainThreadCount = _threads.Length;
            _AfterWork = (ThreadPriority)afterWork;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void LeadParallel()
        {
            Monitor.Enter(_lock);
        }

        public static void PublishTask() { }

        public unsafe class MatrixParallelWrap
        {

            private Queue<IntPtr>[] _cache;
            private Thread[] _threads;
            private MatrixParallelTaskPackage _wrapTask;

            public MatrixParallelWrap(int id, int wrapSize, bool isFirst)
            {
                ID = id;
                _cache = new Queue<IntPtr>[wrapSize];
                for (int i = 0; i < _cache.Length; i++) {
                    _cache[i] = new Queue<IntPtr>(8);
                }
                _threads = new Thread[wrapSize];
                int begin = isFirst ? 0 : 1,end = wrapSize - 1;
                for (int i = 0; i < end; i++)
                {
                    _threads[i] = new Thread(CommonMatrixParallelCycle)
                    {
                        IsBackground = true,
                        Priority = ThreadPriority.BelowNormal,
                        Name = $"MPT#{ID}_{i}"
                    };
                    _threads[i].Start(new Handle(i, this));
                }
                _threads[end] = new Thread(SchedulerMatrixParallelCycle)
                {
                    IsBackground = true,
                    Priority = ThreadPriority.BelowNormal,
                    Name = $"MPT#{ID}_{end}*"
                };
                _threads[end].Start(new Handle(end, this));
            }

            public ref MatrixParallelTaskPackage WrapTask => ref _wrapTask;

            public int ID { get; init; }

            public Span<IntPtr> EnqueuePackage(Span<IntPtr> packageSpan)
            {
                int idx = 0;
                for (; idx < _cache.Length; idx++) {
                    _cache[idx].Enqueue(packageSpan[idx]);
                }
                return packageSpan[idx..];
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public bool TryGetNextWrapTask(int idInWrap, out IntPtr handle)
            {
                return _cache[idInWrap].TryDequeue(out handle);
            }

            public record class Handle(int InWrapIndex, MatrixParallelWrap Wrap);

        }

        #region ThreadOperation

        private static unsafe void CommonMatrixParallelCycle(object obj)
        {
            MatrixParallelWrap.Handle handle = (obj as MatrixParallelWrap.Handle)!;
            MatrixParallelWrap wrap = handle.Wrap;
            int inWrapIndex = handle.InWrapIndex;
            Thread self = Thread.CurrentThread;
            while (true)
            {
                self.Priority = ThreadPriority.Highest;
                while (wrap.TryGetNextWrapTask(inWrapIndex, out IntPtr ptr)) {
                    ExecuteTaskPackage((MatrixParallelTaskPackage*)ptr);
                }
                _ = Interlocked.Decrement(ref RemainThreadCount);
                self.Priority = _AfterWork;
                _restartEvent.Wait();
            }
        }

        private static unsafe void ExecuteTaskPackage(MatrixParallelTaskPackage* p)
        {
            MatrixKernel* left = p->left, right = p->left, result = p->result;
            int count = p->count;
            ScalarDataPacket* scalar = p->scalerPacket;
            switch (p->ComputeMode)
            {
                case 0:
                    delegate*<MatrixKernel*, MatrixKernel*, void> op_0 = (delegate*<MatrixKernel*, MatrixKernel*, void>)p->executionHandle;
                    for (int i = 0; i < count; i++)
                    {
                        op_0(left, result);
                        left += p->leftStride;
                        result += p->resultStride;
                    }
                    break;
                case 1:
                    delegate*<MatrixKernel*, MatrixKernel*, ScalarDataPacket*, void> op_1 = (delegate*<MatrixKernel*, MatrixKernel*, ScalarDataPacket*, void>)p->executionHandle;
                    for (int i = 0; i < count; i++)
                    {
                        op_1(left, result, scalar);
                        left += p->leftStride;
                        result += p->resultStride;
                    }
                    break;
                case 2:
                    delegate*<MatrixKernel*, MatrixKernel*, MatrixKernel*, void> op_2 = (delegate*<MatrixKernel*, MatrixKernel*, MatrixKernel*, void>)p->executionHandle;
                    for (int i = 0; i < count; i++)
                    {
                        op_2(left, right, result);
                        right += p->rightStride;
                        left += p->leftStride;
                        result += p->resultStride;
                    }
                    break;
                case 3:
                    delegate*<MatrixKernel*, MatrixKernel*, MatrixKernel*, ScalarDataPacket*, void> op_3 = (delegate*<MatrixKernel*, MatrixKernel*, MatrixKernel*, ScalarDataPacket*, void>)p->executionHandle;
                    for (int i = 0; i < count; i++)
                    {
                        op_3(left, right, result, scalar);
                        right += p->rightStride;
                        left += p->leftStride;
                        result += p->resultStride;
                    }
                    break;
                default:
                    break;
            }
        }

        private static unsafe void SchedulerMatrixParallelCycle(object obj)
        {
            MatrixParallelWrap.Handle handle = (obj as MatrixParallelWrap.Handle)!;
            MatrixParallelWrap wrap = handle.Wrap;
            int inWrapIndex = handle.InWrapIndex;
            Thread self = Thread.CurrentThread;
            ref MatrixParallelTaskPackage wt = ref wrap.WrapTask, tt = ref TotalTask;
            int l1 = wt

            while (true)
            {
                self.Priority = ThreadPriority.Highest;
                while (wrap.TryGetNextWrapTask(inWrapIndex, out IntPtr ptr)) {
                    ExecuteTaskPackage((MatrixParallelTaskPackage*)ptr);
                }
                _ = Interlocked.Decrement(ref RemainThreadCount);
                self.Priority = _AfterWork;
                _restartEvent.Wait();
            }
        }

        #endregion
    }

    public enum SleepMode
    {

        QuickWakeup = ThreadPriority.AboveNormal,
        NormalSleep = ThreadPriority.BelowNormal,
        DeepSleep = ThreadPriority.Lowest,

    }
}