//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="SlabAllocator.Fixed.cs"
// 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 StgSharp.Mathematics.Memory;
using StgSharp.Threading;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace StgSharp.HighPerformance.Memory
{
    internal unsafe class FixedSlabAllocator<T> : SlabAllocator<T> where T: unmanaged
    {

        private Action<nuint> _freeHandle;

        private bool _disposed;
        private CapacityFixedStack<nuint> _recycle;
        private readonly int _elementSize = Unsafe.SizeOf<T>();

        private nuint _buffer;

        private nuint _Capacity, _currentIndex;

        internal FixedSlabAllocator(nuint buffer, nuint count, Action<nuint> freeHandle)
        {
            _freeHandle = freeHandle;
            _buffer = buffer;

            _Capacity = count;
            int initCount = count switch
            {
                <= 4 => 4,
                > 64 => 64,
                _ => (int)count
            };
            Span<nuint> span = stackalloc nuint[initCount];
            for (int i = 0; i < initCount; i++) {
                span[i] = _buffer + (nuint)(i * _elementSize);
            }
            _recycle = CapacityFixedStackBuilder.Create(span);
            _Capacity = count;
            _currentIndex = (nuint)initCount;
        }

        public override nuint Allocate()
        {
            if (_recycle.TryPop(out nuint handle)) {
                return handle;
            }

            // nuint bufferHandle = _currentBuffer;
            nuint curIndex = _currentIndex;
            if (curIndex >= _Capacity) {
                return 0;
            }
            curIndex = _currentIndex;
            _currentIndex += 1;
            return _buffer + ((nuint)_elementSize * curIndex);
        }

        public override void Dispose()
        {
            if (_disposed) {
                return;
            }
            _disposed = true;
            _freeHandle(_buffer);
            _recycle = null!;
            GC.SuppressFinalize(this);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public override void EnterBufferReading() { }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public override void ExitBufferReading() { }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public override void Free(nuint index)
        {
            _recycle.Push(index);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public override SlabAllocationHandle<T> ReadAllocation()
        {
            return new SlabAllocationHandle<T>(this, false);
        }

        ~FixedSlabAllocator()
        {
            Dispose();
        }

    }
}