//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="HLSFAllocator.Alloc"
// 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 System;
using System.Numerics;

using hlsfHandle = StgSharp.HighPerformance.Memory.HybridLayerSegregatedFitAllocationHandle;

namespace StgSharp.HighPerformance.Memory
{
    public unsafe partial class HybridLayerSegregatedFitAllocator
    {

        public hlsfHandle Alloc(uint size)
        {
            ArgumentOutOfRangeException.ThrowIfGreaterThan<nuint>(size, (nuint)levelSizeArray[^1] * 2);
            int level = GetLevelFromSize(size);
            int segmentIndex = DetermineSegmentIndex(size, level);

            int i = level, s = segmentIndex;
            Entry* handle;
            while (!TryPopLevelForAllocation(i, s, out handle))
            {
                if (++s >= 3)
                {
                    s = 0;
                    i++;
                }
                if (i >= levelSizeArray.Length)
                {
                    if (TryAllocateNew16MBBlock(out handle))
                    {
                        break;
                    }
                    throw new OverflowException("Out of memory: Unable to allocate new 16MB block or find suitable bucket for allocation.");
                }
            }

            if (handle != null)
            {
                int requestedOffset = (segmentIndex + 1) * levelSizeArray[level];
                if ((ulong)requestedOffset > handle->Size)
                {
                    // spare返回的块不足以切出目标大小，避免进入切片导致下溢/越界
                    throw new OverflowException("Out of memory: insufficient block size returned from spare memory.");
                }
                Entry* extra = (Entry*)_entries.Allocate();
                extra->Position = handle->Position + (nuint)requestedOffset;
                extra->Size = handle->Size - (uint)requestedOffset;
                extra->State = EntryState.Empty;
                extra->NextNear = handle->NextNear;
                extra->PreviousNear = handle;
                extra->NextNear->PreviousNear = extra;
                extra->PreviousNear->NextNear = extra;
                SliceMemory(extra);
            }
            handle->State = EntryState.Allocated;
            handle->Level = level;
            return new hlsfHandle(handle, size);
        }

        private void SliceMemory(Entry* e)
        {
            Entry* current = e;
            Entry* next = e->NextNear;
            ulong originOffset = e->Position - (ulong)m_Buffer;
            ulong finalOffset = originOffset;
            ulong end = e->Position + e->Size;
            ulong endOffset = end - (ulong)m_Buffer;
            ulong remainSize = e->Size;


            if (finalOffset >= endOffset || remainSize == 0) {
                return;
            }

            // get level of left edge 
            int minLevel = int.Max((BitOperations.TrailingZeroCount(finalOffset) - 6) / 2, 0);
            int i = minLevel >= levelSizeArray.Length ? levelSizeArray.Length - 1 : minLevel;

            for (; i < levelSizeArray.Length; i++)
            {
                int levelSize = levelSizeArray[i];
                ulong levelLong = (ulong)levelSize;
                ulong levelUpper = levelLong * 4;

                // smallest board that is larger than finalOffset
                ulong board = (finalOffset + levelUpper - 1) / levelUpper * levelUpper;
                long span = (long)ulong.Min(board, endOffset) - (long)finalOffset;
                int blockCount = (span <= 0) ? 0 : (int)(span / (long)levelLong);
                if (blockCount == 0)
                {
                    continue;
                }
                int s = blockCount * levelSize;

                // create and init new entry
                Entry* newEntry = (Entry*)_entries.Allocate();
                newEntry->State = EntryState.Empty;
                newEntry->Position = (nuint)m_Buffer + (nuint)finalOffset;
                newEntry->Size = (uint)s;
                BucketNode* bucket = (BucketNode*)newEntry->Position;
                bucket->EntryRef = newEntry;
                newEntry->Level = i;

                // link new entry
                newEntry->PreviousNear = current;
                newEntry->NextNear = next;
                current->NextNear = newEntry;
                next->PreviousNear = newEntry;

                // set new entry
                current = newEntry;

                PushLevel(i, Math.Min(blockCount - 1, 2), bucket);

                finalOffset += (ulong)s;
                remainSize -= (ulong)s;
                if (remainSize <= (ulong)levelSize)
                {
                    break;
                }
                if (remainSize == 0) {
                    return;
                }
            }

            if (i >= 10)
            {
                int levelSize = levelSizeArray[^1] * 4;
                ulong levelLong = (ulong)levelSize;
                ulong board = endOffset / levelLong * levelLong;
                long span = (long)board - (long)finalOffset;
                int blockCount = span > 0 ? (int)(span / (long)levelSize) : 0;
                if (blockCount > 0)
                {
                    int s = blockCount * levelSize;
                    Entry* newEntry = (Entry*)_entries.Allocate();
                    newEntry->State = EntryState.Empty;
                    newEntry->Position = (nuint)((ulong)m_Buffer + finalOffset);
                    newEntry->Size = (uint)s;
                    BucketNode* bucket = (BucketNode*)newEntry->Position;
                    bucket->EntryRef = newEntry;
                    newEntry->Level = 10;

                    // link new entry
                    newEntry->PreviousNear = current;
                    newEntry->NextNear = next;
                    current->NextNear = newEntry;
                    if (next != null) {
                        next->PreviousNear = newEntry;
                    }

                    newEntry->Level = i;
                    PushLevel(i, Math.Min(blockCount - 1, 2), bucket);

                    finalOffset += (ulong)s;
                    remainSize -= (ulong)s;
                }
                if (remainSize == 0) {
                    return;
                }
            }

            for (i -= 1; i >= 0; i--)
            {
                int levelSize = levelSizeArray[i];
                ulong levelLong = (ulong)levelSize;
                ulong board = endOffset / levelLong * levelLong;
                long span = (long)board - (long)finalOffset;
                int blockCount = span > 0 ? (int)(span / levelSize) : 0;
                if (blockCount <= 0)
                {
                    continue;
                }
                int s = blockCount * levelSize;
                System.Diagnostics.Debug.Assert(finalOffset + (ulong)s <= endOffset);

                // create and init new entry
                Entry* newEntry = (Entry*)_entries.Allocate();
                newEntry->State = EntryState.Empty;
                newEntry->Position = (nuint)((ulong)m_Buffer + finalOffset);
                newEntry->Size = (uint)s;
                BucketNode* bucket = (BucketNode*)newEntry->Position;
                bucket->EntryRef = newEntry;

                // link new entry
                newEntry->PreviousNear = current;
                newEntry->NextNear = next;
                current->NextNear = newEntry;
                if (next != null) {
                    next->PreviousNear = newEntry;
                }

                newEntry->Level = i;
                PushLevel(i, Math.Min(blockCount - 1, 2), bucket);

                // set new entry
                current = newEntry;

                // update lock and data
                finalOffset += (ulong)s;
                remainSize -= (ulong)s;
                if (remainSize == 0)
                {
                    break;
                }
            }
            RemoveFromPositionChain(e);
        }

        /// <summary>
        ///   Try to allocate a new 16MB block when all buckets are empty
        /// </summary>
        /// <param name="handle">
        ///   Output handle to the allocated Entry
        /// </param>
        /// <returns>
        ///   True if allocation succeeded
        /// </returns>
        private bool TryAllocateNew16MBBlock(out Entry* handle)
        {
            nuint pos = _spareMemory->Position;
            nuint bufferEnd = (nuint)m_Buffer + _size;

            if (pos >= bufferEnd || _spareMemory->Size == 0)
            {
                handle = null;
                return false; // No spare memory available
            }

            nuint desired = (nuint)levelSizeArray[^1] * 4;
            nuint remain = bufferEnd - pos;
            nuint blockSize = desired <= remain ? desired : remain;
            if (blockSize == 0)
            {
                handle = null;
                return false;
            }

            nuint newPos = pos + blockSize;

            // Try to allocate new Entry from slab allocator
            handle = (Entry*)_entries.Allocate();
            handle->Position = pos;
            handle->Size = (uint)blockSize;
            handle->Level = GetLevelFromSize((uint)blockSize);

            // Update spare memory position & remaining size
            _spareMemory->Position = newPos;
            _spareMemory->Size = (uint)(bufferEnd - newPos);

            BucketNode* b = (BucketNode*)handle->Position;
            b->EntryRef = handle;

            // update position linked list
            Entry* previous = _spareMemory->PreviousNear;
            handle->NextNear = _spareMemory;
            handle->PreviousNear = previous;
            _spareMemory->PreviousNear = handle; // Replace Volatile.Write with direct access
            if (previous != null)
            {
                previous->NextNear = handle;
            } else
            {
                _positionHead = handle;
            }

            return true;
        }

        /// <summary>
        ///   Helper method for allocation - converts BucketNode to Entry
        /// </summary>
        private bool TryPopLevelForAllocation(int levelIndex, int sizeIndex, out Entry* entry)
        {
            if (TryPopLevel(levelIndex, sizeIndex, out BucketNode* bucketNode))
            {
                entry = bucketNode->EntryRef;
                return entry != null;
            }
            entry = null;
            return false;
        }

    }
}