//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="MatrixParallel"
// Project: StgSharp
// AuthorGroup: Nitload Space
// Copyright (c) Nitload Space. 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
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//     
// -----------------------------------------------------------------------
// -----------------------------------------------------------------------
using StgSharp.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

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

        private const int RESERVED_THREAD_COUNT = 4;

        private static bool _meaningful;

        private static CapacityFixedStack<MatrixParallelThread> _retiredThreads;

        private static CapacityFixedStack<MatrixParallelThread> _threads;

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

        public static bool IsParallelMeaningful => IsParallelSupported && IsInitialized && _meaningful;

        public static int ContextCount { get; private set; }

        private static bool IsInitialized { get; set; }

        internal static void Init()
        {
            Dictionary<ulong, int> contextMap = [];

            if (IsInitialized) {
                return;
            }
            if (!IsParallelSupported)
            {
                IsInitialized = true;
                return;
            }
            contextMap = [];
            int count = Environment.ProcessorCount;
            bool hasGlobalSimd = false;
            SIMDID globalSimd = default;
            _threads = new(count);
            _retiredThreads = new(RESERVED_THREAD_COUNT);
            for (int i = 0; i < count; i++)
            {
                MatrixParallelThread thread = new(i);
                _threads.Push(thread);
                SpinWait.SpinUntil(() => thread.State == MatrixThreadState.Ready);

                SIMDID simd = thread.Simd;
                ulong mask = simd.Mask;
                contextMap[mask] = contextMap.TryGetValue(mask, out int contextCount) ? (contextCount + 1) : 1;
                globalSimd = hasGlobalSimd ? UniteSIMDID(globalSimd, simd) : simd;
                hasGlobalSimd = true;
            }

            IntrinsicContext globalContext = new();
            LoadIntrinsicFunction(&globalContext, globalSimd.Mask);
            NumericalModule.GlobalContext = globalContext;
            NumericalModule.GlobalIntrinsicMask = globalSimd;
            ContextCount = contextMap.Count;
            if (ContextCount == 1)
            {
                int retireCount = Math.Min(RESERVED_THREAD_COUNT, Math.Max(0, _threads.Count));
                for (int i = 0; i < retireCount; i++) {
                    RetireThread(_threads.Pop());
                }
            } else
            {
                MatrixParallelThread[] allThreads = _threads.PopRange(_threads.Count);
                Array.Sort(allThreads, static(left, right) => CompareSIMDID(left.Simd, right.Simd));
                int retireCount = Math.Min(RESERVED_THREAD_COUNT, Math.Max(0, allThreads.Length - 1));
                for (int i = 0; i < retireCount; i++) {
                    RetireThread(allThreads[i]);
                }
                _threads.PushRange(allThreads.AsSpan(retireCount));
            }
            _meaningful = _threads.Count > 1;
            _awaitingLeaderHandle = new AwaitingQueue();
            IsInitialized = true;
        }

        [LibraryImport(Native.LibName, EntryPoint = "sn_compare_simd")]
        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
        [DefaultDllImportSearchPaths(DllImportSearchPath.AssemblyDirectory)]
        private static partial int CompareSIMDID(SIMDID left, SIMDID right);

        [LibraryImport(Native.LibName, EntryPoint = "load_intrinsic_function")]
        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
        [DefaultDllImportSearchPaths(DllImportSearchPath.AssemblyDirectory)]
        private static partial void LoadIntrinsicFunction(IntrinsicContext* context, ulong id);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void RetireThread(MatrixParallelThread thread)
        {
            thread.Retire();
            _retiredThreads.Push(thread);
        }

        [LibraryImport(Native.LibName, EntryPoint = "sn_get_unite_simd")]
        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
        [DefaultDllImportSearchPaths(DllImportSearchPath.AssemblyDirectory)]
        private static partial SIMDID UniteSIMDID(SIMDID left, SIMDID right);

    }
}