//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="MatrixPanel"
// 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
// 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.Internal;
using System;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace StgSharp.HighPerformance
{
    public unsafe struct MatrixPanel
    {

        private byte Head;

    }

    // Single POD-style panel: ZMM-compatible size. Alignment handled by allocator, not by the struct.
    public unsafe struct MatrixPanel<T> where T : unmanaged, INumber<T>
    {

        public const int AlignmentBytes = 64;

        internal T Head; // first element of the panel buffer

        public ref T this[int column, int row]
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get => ref Unsafe.Add(ref Head, row * ElementSideLength + column);
        }

        public static int ElementSideLength
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get => Math.Max(8, AlignmentBytes / sizeof(T));
        }

        public static int MaxElementCount
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get => ElementSideLength * ElementSideLength;
        }

        public static nuint Size
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get => (nuint)(MaxElementCount * sizeof(T));
        }

        public Span<T> Elements
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get
            {
                ref T first = ref Head;
                unsafe
                {
                    void* p = Unsafe.AsPointer(ref first);
                    return new Span<T>(p, MaxElementCount);
                }
            }
        }

        // Allocate aligned memory for one panel; caller must free via Destroy.
        public static unsafe MatrixPanel<T>* Create()
        {
            return (MatrixPanel<T>*)NativeMemory.AlignedAlloc(Size, AlignmentBytes);
        }

        public static unsafe void Destroy(MatrixPanel<T>* panel)
        {
            NativeMemory.AlignedFree(panel);
        }

        // View an existing pointer; caller guarantees lifetime/alignment.
        public static unsafe MatrixPanel<T>* FromPointer(void* ptr)
        {
            return (MatrixPanel<T>*)Align64(ptr);
        }

        /// <summary>
        ///   Number of 4x4 kernels that fit in a panel for the given ISA and element T.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static int KernelCapacity()
        {
            int perSide = KernelSideCount();
            return perSide * perSide;
        }

        /// <summary>
        ///   How many 4x4 kernels fit along a single panel dimension for the given ISA.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static int KernelSideCount()
        {
            return NativeIntrinsic.IntrinsicLevel switch
            {
                IntrinsicLevel.SSE => KernelSideCountSse(),
                IntrinsicLevel.AVX2 => KernelSideCountAvx2(),
                IntrinsicLevel.AVX512 => KernelSideCountAvx512(),
                _ => 0
            };
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static unsafe nuint Align64(void* p) => ((nuint)p + (AlignmentBytes - 1)) & ~(nuint)(AlignmentBytes - 1);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static int KernelSideCountAvx2()
        {
            const int minQ = 8;
            int lanes = 32 / sizeof(T);
            int side = Math.Max(lanes, minQ);
            return side / 4;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static int KernelSideCountAvx512()
        {
            const int minQ = 8;
            int lanes = 64 / sizeof(T);
            int side = Math.Max(lanes, minQ);
            return side / 4;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static int KernelSideCountSse()
        {
            const int minQ = 4;
            int lanes = 16 / sizeof(T);
            int side = Math.Max(lanes, minQ);
            return side / 4;
        }

    }
}