// -----------------------------------------------------------------------------
// file="Matrix"
// Project: StgSharp
// Copyright (c) Nitload.
// SPDX-License-Identifier: MIT
// -----------------------------------------------------------------------------

using StgSharp.Mathematics;
using StgSharp.Mathematics.Numeric;
using System;
using System.Numerics;
using System.Runtime.CompilerServices;

// using hlsfHandle = global::StgSharp.HighPerformance.Memory.HybridLayerSegregatedFitAllocationHandle;

namespace StgSharp.Mathematics.Numeric
{
    public unsafe partial class Matrix<T> where T : unmanaged, INumber<T>
    {

        private protected static readonly int t_count = 16 / sizeof(T);

        private protected static readonly int t_size = sizeof(T);
        private readonly MatrixKernelBoarder _boarder;
        private readonly MatrixSize _size;
        private readonly MatrixStorage<T> _buffer;

        private protected Matrix(
                          MatrixKernelBoarder boarder,
                          MatrixSize size,
                          MatrixStorage<T> buffer

        )
        {
            _boarder = boarder;
            _size = size;
            _buffer = buffer;
        }

        public T this[
                 int x,
                 int y
        ]
        {
            get
            {
                if ((y < 0) ||
                    (y > _size.ElementColumnLength) ||
                    (x < 0) ||
                    (x > _size.ElementRowLength)) {
                    throw new ArgumentOutOfRangeException($"Index [{x},{y}] is out of matrix index range.");
                }
                long offset = GetElementOffset(x, y);
                if (offset < 0) {
                    return T.Zero;
                }
                return ((T*)Buffer)[offset];
            }
            set
            {
                if ((y < 0) ||
                    (y > _size.ElementColumnLength) ||
                    (x < 0) ||
                    (x > _size.ElementRowLength)) {
                    throw new ArgumentOutOfRangeException($"Index [{x},{y}] is out of matrix index range.");
                }
                long offset = GetElementOffset(x, y);
                if (offset < 0) {
                    return;
                }
                ((T*)Buffer)[offset] = value;
            }
        }

        /// <summary>
        ///   Matlab style indexer to generate a new matrix
        /// </summary>
        /// <param name="column">
        ///
        /// </param>
        /// <param name="row">
        ///
        /// </param>
        /// <returns>
        ///
        /// </returns>
        /// <exception cref="NotImplementedException">
        ///
        /// </exception>
        public unsafe Matrix<T> this[
                                ReadOnlySpan<MatrixIndex> column,
                                ReadOnlySpan<MatrixIndex> row
        ]
        {
            get => throw new NotImplementedException();
            set => throw new NotImplementedException();
        }

        /// <summary>
        ///   Length of the matrix in columns.
        /// </summary>
        public int ColumnLength => _size.ElementColumnLength;

        /// <summary>
        ///   Length of the matrix in rows.
        /// </summary>
        public int RowLength => _size.ElementRowLength;

        public MatrixLayout Layout { get; init; }

        internal MatrixKernel<T>* Buffer => (MatrixKernel<T>*)_buffer.BufferPointer;

        protected internal int KernelColumnLength => _size.KernelColumnLength;

        protected internal int KernelRowLength => _size.KernelRowLength;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe ref MatrixKernel<T> GetMatrixKernel(
                                          int x,
                                          int y
        )
        {
            return ref (_boarder.IsInBuffer(x, y, in _size) ?
                        ref _buffer[_boarder.GetIndexOffset(x, y, in _size)] :
                        ref Unsafe.NullRef<MatrixKernel<T>>());
        }

        internal long GetElementOffset(
                      int x,
                      int y
        )
        {
            int
                k_c = y / 4,
                c = y % 4,
                k_r = x / 4,
                r = x % 4;
            if (!_boarder.IsInBuffer(k_r, k_c, in _size)) {
                return -1;
            }
            long kernelOffset = _boarder.GetIndexOffset(k_r, k_c, in _size);

            return (kernelOffset * 16) + (4 * r) + c;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal unsafe ref T GetElementUnsafe(
                              int x,
                              int y
        )
        {
            // Caller guarantees: indices in range, layout is dense square.
            int k_c = y / 4;
            int k_r = x / 4;
            int c = y % 4;
            int r = x % 4;

            ref MatrixKernel<T> kernel = ref _buffer[_boarder.GetIndexOffset(k_r, k_c, in _size)];
            return ref kernel[c, r];
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal unsafe MatrixKernel<T>* GetKernelAddressUnsafe(
                                         int x,
                                         int y
        )
        {
            return Buffer + _boarder.GetIndexOffset(x, y, in _size);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal unsafe ref MatrixKernel<T> GetKernelUnsafe(
                                            int x,
                                            int y
        )
        {
            // Caller guarantees: indices in range, layout is dense square.
            int k_c = y / 4;
            int k_r = x / 4;
            return ref _buffer[_boarder.GetIndexOffset(k_c, k_r, in _size)];
        }

    }
}