//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="HLSFAllocator.SegmentEntry.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 System;
using System.Linq.Expressions;
using System.Reflection.PortableExecutable;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;
using System.Threading;

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

        private static void AcquireEntrySpinLock(Entry* entry)
        {
            // 使用新的双锁设计，获取两个锁
            if (entry != null)
            {
                entry->AcquirePrevLock();
                entry->AcquireNextLock();
            }
        }

        private bool AssertAlignBoundry(ulong current, Entry* target, int level)
        {
            int size = (level * 2) + 6;
            ulong align = current >> size;
            return align == target->Position >> size && align == target->Size;
        }

        /// <summary>
        ///   Determine segment index based on size and originLevel
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private int DetermineSegmentIndex(uint size, int level)
        {
            return (int)size / levelSize[level];
        }

        /// <summary>
        ///   Check if two Entries are adjacent in memory
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsAdjacentTo(Entry* current, Entry* other)
        {
            // Check if this immediately follows other
            return other->Position + other->Size == current->Position ||
                   current->Position + current->Size == other->Position;
        }

        /// <summary>
        ///   Used in Free operations, efficiently remove from buckets and merge adjacent blocks.
        ///   Current Entry will serve as the final merged block. The Merge will be in lazy
        ///   stretagey, any fail in acquiring spin lock will end a merging process.
        /// </summary>
        private Entry* MergeAndRemoveFromBuckets(Entry* entry)
        {
            if (entry == null) {
                return null;
            }

            Entry* result = entry;
            uint size = entry->Size;
            int originLevel = GetLevelFromSize(size);
            int segment = DetermineSegmentIndex(size, originLevel);

            if (!TryAcquireEntrySpinLock(entry))
            {
                return entry; // 无法获取锁，返回原Entry
            }

            try
            {
                // 设置状态为合并中
                entry->TrySetState(EntryState.Empty, EntryState.Merging);


                // current Level merge
                while (originLevel <= entry->Level)
                {
                    ulong offset = entry->Position - (ulong)m_Buffer;


                    // backward merging - 向前合并
                    while (true)
                    {
                        ulong p = entry->PreviousNear;
                        Entry* prev = (Entry*)p;
                        if (prev == null ||
                            prev->GetState() != EntryState.Empty ||
                            !IsAdjacentTo(entry, prev) ||
                            entry->Level != prev->Level ||
                            !AssertAlignBoundry(offset, prev, entry->Level) ||
                            !TryAcquireEntrySpinLock(prev))
                        {
                            break;
                        }

                        try
                        {
                            RemoveFromBucket(originLevel, segment, (BucketNode*)prev->Position);
                            MergeEntry(entry, prev);
                            RecycleEntry(prev);
                        }
                        finally
                        {
                            ReleaseEntrySpinLock(prev);
                        }
                    }

                    // forward merging - 向后合并
                    while (true)
                    {
                        ulong n = entry->NextNear;
                        Entry* next = (Entry*)n;
                        if (next == null ||
                            next->GetState() != EntryState.Empty ||
                            !IsAdjacentTo(entry, next) ||
                            entry->Level != next->Level ||
                            !AssertAlignBoundry(offset, next, entry->Level) ||
                            !TryAcquireEntrySpinLock(next))
                        {
                            break;
                        }

                        try
                        {
                            RemoveFromBucket(originLevel, segment, (BucketNode*)next->Position);
                            MergeEntry(entry, next);
                            RecycleEntry(next);
                        }
                        finally
                        {
                            ReleaseEntrySpinLock(next);
                        }
                    }


                    // 更新level信息
                    originLevel++;
                    if (originLevel > entry->Level)
                    {
                        break;
                    }
                }


                // 恢复状态为空
                entry->TrySetState(EntryState.Merging, EntryState.Empty);
                return entry;
            }
            finally
            {
                ReleaseEntrySpinLock(entry);
            }
        }

        private void MergeEntry(Entry* remain, Entry* other)
        {
            if (other == null) {
                return;
            }

            // Determine merged starting position and size
            nuint newPosition = remain->Position < other->Position ? other->Position : other->Position;
            uint newSize = remain->Size + other->Size;

            // Update current Entry
            remain->Position = newPosition;
            remain->Size = newSize;
        }

        private void RecycleEntry(Entry* entry)
        {
            if (entry is null) {
                return;
            }
            entry-> PreviousNear = EmptyHandle;
            entry-> Position = EmptyHandle;
            _nodes.Free((nuint)entry);
        }

        private static void ReleaseEntrySpinLock(Entry* entry)
        {
            // 使用新的双锁设计，释放两个锁
            if (entry != null)
            {
                entry->ReleaseBothLocks();
            }
        }

        /// <summary>
        ///   Remove node from position linked list
        /// </summary>
        private void RemoveFromPositionChain(Entry* entry)
        {
            AcquireEntrySpinLock(entry);
            try
            {
                Entry* prev = (Entry*)entry->PreviousNear;
                Entry* next = (Entry*)entry->NextNear;

                if (prev != null) {
                    prev->NextNear = entry->NextNear;
                }
                if (next != null) {
                    next->PreviousNear = entry->PreviousNear;
                }

                // Clear node pointers
                entry->NextNear = EmptyHandle;
                entry->PreviousNear = EmptyHandle;
                _nodes.Free((nuint)entry);
            }
            finally
            {
                ReleaseEntrySpinLock(entry);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool TryAcquireEntrySpinLock(Entry* entry)
        {
            // 使用新的双锁设计，尝试获取两个锁
            return entry == null || entry->TryAcquireBothLocks();
        }

        /// <summary>
        ///   Entry structure - streamlined version (only position and state information) Stored in
        ///   external SLAB
        /// </summary>
        [StructLayout(LayoutKind.Explicit, Size = 44)]
        internal struct Entry
        {

            [FieldOffset(28)] internal int Level;           // Level of the block in the allocator
            [FieldOffset(40)] internal int NextLock;        // 后继指针锁（控制NextNear指针操作）

            // 双锁设计：分离前后指针操作（和BucketNode保持一致）
            [FieldOffset(36)] internal int PrevLock;        // 前驱指针锁（控制PreviousNear指针操作）
            [FieldOffset(32)] internal int State;           // Node state (using int for atomic operations)
            [FieldOffset(24)] internal uint Size;           // Block size information
            [FieldOffset(8)]  internal ulong NextNear;      // Position linked list: next pointer
            [FieldOffset(16)] internal ulong PreviousNear;  // Position linked list: previous pointer
            [FieldOffset(0)]  public nuint Position;        // Memory block position

        }

        // 更新后的EntryState常量类 - 使用int类型
        private static class EntryState
        {

            public const int Allocated = 1;       // Already allocated to user
            public const int Empty = 0;           // Free, can be allocated
            public const int Merging = 3;         // Currently being merged
            public const int ThreadOccupied = 2;  // Occupied by thread (being operated on)

        }

    }
}