//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="TwoLayerSegregatedFitAllocator"
// 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.HighPerformance.Memory;
using StgSharp.HighPerformance.ProcessorAbstraction;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Numerics;
using System.Reflection.Metadata;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using static StgSharp.HighPerformance.Memory.TwoLayerSegregatedFitAllocator;

namespace StgSharp.HighPerformance.Memory
{
    public unsafe class TwoLayerSegregatedFitAllocator : IDisposable
    {

        private const ulong Mask48Bits = 0x0000FFFFFFFFFFFF;

        private readonly int[] _bucket;
        private readonly Metadata* _spareMemory;
        private readonly Action<nuint> _freeHandle;
        private bool disposedValue;
        private readonly int _align;

        private int _metadataEnd;
        private readonly Ptr64 _basePtr;
        private readonly ulong _maxAllocSize;
        private readonly ulong _totalSize;

        internal TwoLayerSegregatedFitAllocator(
                 nuint byteSize,
                 int align,
                 ulong maxBlockSize,
                 Func<nuint, int, nuint> allocator,
                 Action<nuint> freeHandle
        )
            : this(byteSize, align, maxBlockSize, (void*)allocator(byteSize, align), freeHandle) { }

        internal TwoLayerSegregatedFitAllocator(
                 nuint byteSize,
                 int align,
                 ulong maxBlockSize,
                 void* externalPointer,
                 Action<nuint> freeHandle
        )
        {
            _totalSize = byteSize;
            _basePtr = (Ptr64)(ulong)externalPointer;
            _align = align;
            _maxAllocSize = ulong.Max(64, (~64UL) & (ulong.Min(maxBlockSize + 63, Mask48Bits)));
            _bucket = new int[GetLevel(_maxAllocSize) + 1];
            _spareMemory = &((Metadata*)(ulong)(_basePtr + _totalSize))[-1];
            _freeHandle = freeHandle ?? (static_ => { });
            _metadataEnd = 0;

            // init spare memory node

            _spareMemory->Position = 0UL;
            _spareMemory->Size = _totalSize - Metadata.SizeOf;
            _spareMemory->NextLevel = 0;
            _spareMemory->NextNear = 0;
            _spareMemory->PreviousLevel = 0;
            _spareMemory->PreviousNear = 0;
        }

        public TwoLayerSegregatedFitAllocator(
               nuint byteSize
        )
            : this(byteSize, 16, 32U * 1024U * 1024U, NativeMemory.AlignedAlloc(byteSize, 16),
                   ptr => NativeMemory.AlignedFree((void*)ptr)) { }

        public TwoLayerSegregatedFitAllocator(
               nuint byteSize,
               uint maxBlockSize
        )
            : this(byteSize, 16, maxBlockSize, NativeMemory.AlignedAlloc(byteSize, 16),
                   ptr => NativeMemory.AlignedFree((void*)ptr)) { }

        public TwoLayerSegregatedFitAllocator(
               nuint byteSize,
               int align
        )
            : this(byteSize, align, 32U * 1024U * 1024U, NativeMemory.AlignedAlloc(byteSize, 16),
                   ptr => NativeMemory.AlignedFree((void*)ptr)) { }

        public TwoLayerSegregatedFitAllocator(
               nuint byteSize,
               int align,
               nuint maxBlockSize
        )
            : this(byteSize, align, maxBlockSize, NativeMemory.AlignedAlloc(byteSize, 16),
                   ptr => NativeMemory.AlignedFree((void*)ptr)) { }

        public Handle Alloc(
                      nuint size
        )
        {
            ulong allocSize = ulong.Max(64, (~63UL) & ((ulong)size + 63));
            if (allocSize > _maxAllocSize) {
                throw new OverflowException("Requested allocation size exceeds the maximum block size.");
            }
            int level = GetLevel(allocSize);
            Metadata* entry = null;
            for (int i = level; i < _bucket.Length; i++)
            {
                int idx = _bucket[i];
                if (idx != 0)
                {
                    entry = &_spareMemory[-idx];
                    _bucket[i] = entry->NextLevel;
                    break;
                }
            }
            if (entry is null && !TryAllocNewChunk(allocSize, out entry)) {
                throw new OverflowException("No available ");
            }
            int entryIdx = (int)(_spareMemory - entry);
            ulong entrySize = entry->Size;
            ulong remain = entrySize - allocSize;

            // slice tail
            if (remain > (entrySize >> 7) && TryGetNewMetadata(out Metadata* newEntry))
            {
                int newEntryIdx = (int)(_spareMemory - newEntry);
                newEntry->Position = entry->Position + allocSize;
                newEntry->Size = remain;
                int newLevel = GetLevel(remain);
                int bucketHeadIdx = _bucket[newLevel];
                if (bucketHeadIdx != 0)
                {
                    // if there is already an entry in the bucket, link it to the new entry
                    Metadata* bucketHead = &_spareMemory[-bucketHeadIdx];
                    newEntry->NextLevel = bucketHeadIdx;
                    bucketHead->PreviousLevel = newEntryIdx;
                } else
                {
                    newEntry->NextLevel = 0;
                }
                newEntry->PreviousLevel = 0;
                _bucket[newLevel] = newEntryIdx;

                // push to position chain
                int afterIdx = entry->NextNear;
                Metadata* after = &_spareMemory[-afterIdx];
                newEntry->NextNear = afterIdx;
                after->PreviousNear = newEntryIdx;
                entry->NextNear = newEntryIdx;
                newEntry->PreviousNear = entryIdx;
            }
            return new Handle(entry, _basePtr);
        }

        public void Collect() { }

        public void Dispose()
        {
            Dispose(disposing:true);
            GC.SuppressFinalize(this);
        }

        public void Free(
                    Handle handle,
                    int collectScanWindow = 4
        )
        {
            Metadata* head = handle._meta;
            for (int i = 0; i < collectScanWindow; i++)
            {
                // forward scan
            }
            for (int i = 0; i < collectScanWindow; i++)
            {
                // backward scan
            }
        }

        public bool TryAlloc(
                    nuint size,
                    out Handle h
        )
        {
            throw new NotImplementedException();
        }

        protected virtual void Dispose(
                               bool disposing
        )
        {
            if (!disposedValue)
            {
                if (disposing) {
                    _freeHandle((nuint)_basePtr);
                }

                disposedValue = true;
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static int GetLevel(
                           ulong size
        )
        {
            return 57 - BitOperations.LeadingZeroCount(size);
        }

        private bool TryAllocNewChunk(
                     ulong size,
                     out Metadata* meta
        )
        {
            int idx = _spareMemory->NextLevel;
            if (idx != 0)
            {
                meta = &_spareMemory[-idx];
                _spareMemory->NextLevel = meta->NextLevel;
                return true;
            }
            ulong spareSize = _spareMemory->Size;
            if (spareSize < Metadata.SizeOf + size)
            {
                meta = null;
                return false;
            }
            _metadataEnd++;
            meta = &_spareMemory[-_metadataEnd];
            spareSize -= Metadata.SizeOf + size;
            _spareMemory->Size = spareSize;
            _spareMemory->Position += size;
            meta->Size = size;

            // insert the new chunk to position chain
            int nearIdx = _spareMemory->PreviousNear;
            Metadata* near = &_spareMemory[-nearIdx];
            near->NextNear = _metadataEnd;
            meta->PreviousNear = nearIdx;
            _spareMemory->PreviousNear = _metadataEnd;
            meta->NextNear = 0;
            return true;
        }

        private bool TryGetNewMetadata(
                     out Metadata* meta
        )
        {
            ulong spareSize = _spareMemory->Size;
            if (spareSize < Metadata.SizeOf)
            {
                meta = null;
                return false;
            }
            _metadataEnd++;
            meta = &_spareMemory[-_metadataEnd];
            spareSize -= Metadata.SizeOf;
            _spareMemory->Size = spareSize;
            return true;
        }

        [StructLayout(LayoutKind.Explicit)]
        public readonly struct Handle
        {

            [FieldOffset(0)]internal readonly Metadata* _meta;
            [FieldOffset(8)]public readonly void* Pointer;
            [FieldOffset(16)]public readonly Ptr64 Size;

            internal Handle(
                     Metadata* meta,
                     Ptr64 baseAddress
            )
            {
                _meta = meta;
                Pointer = (void*)(ulong)(meta->Position + baseAddress);
                Size = meta->Size;
            }

            [Obsolete("You should not create instance from default. Alloc from allocator please")]
            public Handle() { }

            public ref byte this[
                            int offset
            ] => ref ((byte*)Pointer)[offset];

            public Span<byte> AsSpan(
                              int range = -1
            )
            {
                return new Span<byte>(Pointer, range < 0 ? (int)(ulong)Size : range);
            }

        }

        internal enum AllocationState : short
        {

            Free = 0,
            Used = 1,
            Split = 2,
            Merged = 3

        }

        [StructLayout(LayoutKind.Explicit, Size = 32)]
        internal struct Metadata
        {

            [FieldOffset(24)] private ulong PositionMask;
            [FieldOffset(16)] private ulong SizeMask;

            [FieldOffset(30)] internal AllocationState State;

            [FieldOffset(0)] public int NextLevel;
            [FieldOffset(4)] public int NextNear;
            [FieldOffset(8)] public int PreviousLevel;
            [FieldOffset(12)] public int PreviousNear;

            public Ptr64 Position
            {
                readonly get => PositionMask;
                set => PositionMask = value;
            }

            public Ptr64 Size
            {
                readonly get => (Ptr64)(SizeMask & Mask48Bits);
                set => SizeMask = (SizeMask & ~Mask48Bits) | ((ulong)value & Mask48Bits);
            }

            public Ptr64 SizeForSpare
            {
                readonly get => SizeMask;
                set => SizeMask = value;
            }

            public static uint SizeOf { get; } = (uint)Unsafe.SizeOf<Metadata>();

        }

    }
}