//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="MatrixParallel.Await"
// Project: StgSharp
// AuthorGroup: Nitload
// Copyright (c) Nitload. All rights reserved.
//     
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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//     
// -----------------------------------------------------------------------
// -----------------------------------------------------------------------
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace StgSharp.Mathematics.Numeric
{
    public static partial class MatrixParallel
    {

        private static ConcurrentQueue<WaitHandle> _awaitingLeaderHandle;

        private static volatile int _createGeneration = 0;
        private static int _sortState;

        public static MatrixParallelThread[] LeadParallel(int recommendCount)
        {
            int min = int.Min(recommendCount, _threads.Capacity);
            min /= 2;
            MatrixParallelThread[] ret;
            if (_threads.Count < min)
            {
                WaitHandle handle = new WaitHandle
                {
                    CreateGeneration = _createGeneration,
                    LeastCount = min,
                    BestCount = recommendCount
                };
                _awaitingLeaderHandle.Enqueue(handle);
                int cycleGeneration = _createGeneration;
                while (true)
                {
                    // TODO 排队等待，对前八个按照优先级排序，优先级最高的独占进行等待，其他继续排队
                    if (_createGeneration != cycleGeneration)
                    {
                        if (Interlocked.Exchange(ref _sortState, 1) == 0)
                        {
                            // TODO 排序
                            _ = Interlocked.Exchange(ref _sortState, 0);
                        } else
                        {
                            cycleGeneration = _createGeneration;
                            continue;
                        }
                    }
                    if (_awaitingLeaderHandle.TryPeek(out WaitHandle? p) && p == handle)
                    {
                        // get the leader
                        ret = _threads.PopRange(recommendCount);
                        _awaitingLeaderHandle.TryDequeue(out _);
                        break;
                    }
                    Thread.Sleep(0);
                }
            } else
            {
                // directly get the leader
                ret = _threads.PopRange(recommendCount);
            }
            _ = Interlocked.Increment(ref _createGeneration);
            return ret;
        }

        public static void ReturnParallelResources(ref MatrixParallelThread[] pool)
        {
            _threads.PushRange(pool);
            pool = null!;
        }

        private record class WaitHandle
        {

            public int CreateGeneration { get; set; }

            public int LeastCount { get; set; }

            public int BestCount { get; set; }

            public int CurrentPriority(int currentGeneration)
            {
                return (currentGeneration - CreateGeneration) * (MatrixParallel._threads.Capacity - LeastCount);
            }

        }

    }
}