//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="HLSFAllocator.BucketNode.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.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Threading;

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

        private static void AcquireBucketNodeSpinLock(BucketNode* node)
        {
            // 使用新的静态方法
            BucketNodeOperations.AcquireBothLocks(node);
        }

        /// <summary>
        ///   Initialize bucket system (called in constructor)
        /// </summary>
        private void InitializeBucketSystem()
        {
            _bucketHeads = new ulong[levelSize.Length * 3];
        }

        private void PushLevel(int levelIndex, int sizeIndex, BucketNode* node)
        {
            if (node == null || node->EntryRef == null) {
                return;
            }

            int index = (3 * levelIndex) + sizeIndex;
            if (Interlocked.CompareExchange(ref _bucketHeads[index], (nuint)node, EmptyHandle) == EmptyHandle)
            {
                node->IsInBucket = true;
                node->Magic = BucketNode.MAGIC_NUMBER;
                return;
            } else
            {
                while (true)
                {
                    // 对新节点只需要获取NextLock，因为我们要设置它的NextLevel
                    node->AcquireNextLock();
                    ulong head = Volatile.Read(ref _bucketHeads[index]);
                    node->NextLevel = head;
                    BucketNode* headNode = (BucketNode*)head;

                    try
                    {
                        if (Interlocked.CompareExchange(ref _bucketHeads[index], (nuint)node, head) == head)
                        {
                            // 对头节点只需要获取PrevLock，因为我们要设置它的PreviousLevel
                            if (headNode != null && !headNode->TryAcquirePrevLock())
                            {
                                // reset state and retry
                                _ = Interlocked.CompareExchange(ref _bucketHeads[index], head, (nuint)node);
                                Thread.Sleep(0);
                                continue;
                            }
                            try
                            {
                                node->IsInBucket = true;
                                node->Magic = BucketNode.MAGIC_NUMBER;
                                if (headNode != null) {
                                    headNode->PreviousLevel = (ulong)node;
                                }
                                return;
                            }
                            finally
                            {
                                if (headNode != null) {
                                    headNode->ReleasePrevLock();
                                }
                            }
                        } else
                        {
                            Thread.Sleep(0);
                            continue;
                        }
                    }
                    finally
                    {
                        node->ReleaseNextLock();
                    }
                }
            }
        }

        private static void ReleaseBucketNodeSpinLock(BucketNode* node)
        {
            // 使用新的静态方法
            BucketNodeOperations.ReleaseBothLocks(node);
        }

        private void RemoveFromBucket(int levelIndex, int sizeIndex, BucketNode* node)
        {
            int index = (3 * levelIndex) + sizeIndex;
            while (true)
            {
                // 检查是否是栈顶节点
                if ((BucketNode*)Volatile.Read(ref _bucketHeads[index]) == node)
                {
                    // 栈顶节点直接使用TryPopLevel
                    if (TryPopLevel(levelIndex, sizeIndex, out _))
                    {
                        return;
                    }
                    continue;
                }


                // 中间或底部节点的删除操作
                // 获取当前节点的前后指针（只读操作，暂时不加锁）
                ulong p = Volatile.Read(ref node->PreviousLevel);
                ulong n = Volatile.Read(ref node->NextLevel);
                BucketNode* previous = (BucketNode*)p;
                BucketNode* next = (BucketNode*)n;


                // 按照地址顺序获取锁，避免死锁
                BucketNode* firstLock = null, secondLock = null, thirdLock = null;
                bool needPrevNextLock = false, needNodeBothLocks = false, needNextPrevLock = false;

                if (previous != null && next != null)
                {
                    // 中间节点：需要修改前驱的next和后继的prev
                    if ((ulong)previous < (ulong)node && (ulong)node < (ulong)next)
                    {
                        firstLock = previous;
                        needPrevNextLock = true;
                        secondLock = node;
                        needNodeBothLocks = true;
                        thirdLock = next;
                        needNextPrevLock = true;
                    } else if ((ulong)previous < (ulong)next && (ulong)next < (ulong)node)
                    {
                        firstLock = previous;
                        needPrevNextLock = true;
                        secondLock = next;
                        needNextPrevLock = true;
                        thirdLock = node;
                        needNodeBothLocks = true;
                    } else // other cases
                    {
                        firstLock = next;
                        needNextPrevLock = true;
                        secondLock = previous;
                        needPrevNextLock = true;
                        thirdLock = node;
                        needNodeBothLocks = true;
                    }
                } else if (previous != null)
                {
                    // 尾节点：只需要修改前驱的next
                    if ((ulong)previous < (ulong)node)
                    {
                        firstLock = previous;
                        needPrevNextLock = true;
                        secondLock = node;
                        needNodeBothLocks = true;
                    } else
                    {
                        firstLock = node;
                        needNodeBothLocks = true;
                        secondLock = previous;
                        needPrevNextLock = true;
                    }
                } else
                {
                    // 应该不会到这里，因为头节点已经在上面处理了
                    Thread.Sleep(0);
                    continue;
                }


                // 按顺序获取锁
                bool acquired = false;
                try
                {
                    if (firstLock != null)
                    {
                        if (firstLock == previous && needPrevNextLock)
                        {
                            if (!firstLock->TryAcquireNextLock())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        } else if (firstLock == next && needNextPrevLock)
                        {
                            if (!firstLock->TryAcquirePrevLock())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        } else if (firstLock == node && needNodeBothLocks)
                        {
                            if (!firstLock->TryAcquireBothLocks())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        }
                    }

                    if (secondLock != null)
                    {
                        if (secondLock == previous && needPrevNextLock)
                        {
                            if (!secondLock->TryAcquireNextLock())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        } else if (secondLock == next && needNextPrevLock)
                        {
                            if (!secondLock->TryAcquirePrevLock())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        } else if (secondLock == node && needNodeBothLocks)
                        {
                            if (!secondLock->TryAcquireBothLocks())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        }
                    }

                    if (thirdLock != null)
                    {
                        if (thirdLock == previous && needPrevNextLock)
                        {
                            if (!thirdLock->TryAcquireNextLock())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        } else if (thirdLock == next && needNextPrevLock)
                        {
                            if (!thirdLock->TryAcquirePrevLock())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        } else if (thirdLock == node && needNodeBothLocks)
                        {
                            if (!thirdLock->TryAcquireBothLocks())
                            {
                                Thread.Sleep(0);
                                continue;
                            }
                        }
                    }

                    acquired = true;


                    // 执行链表操作
                    if (previous != null)
                    {
                        previous->NextLevel = n;
                    }
                    if (next != null) {
                        next->PreviousLevel = p;
                    }
                    node->NextLevel = EmptyHandle;
                    node->PreviousLevel = EmptyHandle;
                    node->IsInBucket = false;
                    return;
                }
                finally
                {
                    if (acquired)
                    {
                        // 释放锁
                        if (thirdLock == previous && needPrevNextLock)
                        {
                            thirdLock->ReleaseNextLock();
                        } else if (thirdLock == next && needNextPrevLock)
                        {
                            thirdLock->ReleasePrevLock();
                        } else if (thirdLock == node && needNodeBothLocks) {
                            thirdLock->ReleaseBothLocks();
                        }

                        if (secondLock == previous && needPrevNextLock)
                        {
                            secondLock->ReleaseNextLock();
                        } else if (secondLock == next && needNextPrevLock)
                        {
                            secondLock->ReleasePrevLock();
                        } else if (secondLock == node && needNodeBothLocks) {
                            secondLock->ReleaseBothLocks();
                        }

                        if (firstLock == previous && needPrevNextLock)
                        {
                            firstLock->ReleaseNextLock();
                        } else if (firstLock == next && needNextPrevLock)
                        {
                            firstLock->ReleasePrevLock();
                        } else if (firstLock == node && needNodeBothLocks) {
                            firstLock->ReleaseBothLocks();
                        }
                    }
                }
            }
        }

        private static bool TryAcquireBucketNodeSpinLock(BucketNode* node)
        {
            // 使用新的静态方法
            return BucketNodeOperations.TryAcquireBothLocks(node);
        }

        private bool TryPopLevel(int levelIndex, int sizeIndex, out BucketNode* node)
        {
            int index = (3 * levelIndex) + sizeIndex;
            while (true)
            {
                ulong h = Volatile.Read(ref _bucketHeads[index]);
                BucketNode* head = (BucketNode*)h;

                if (head == null)
                {
                    node = null;
                    return false;
                }


                // 对头节点获取NextLock，因为我们要读取它的NextLevel
                if (!head->TryAcquireNextLock())
                {
                    Thread.Sleep(0);
                    continue;
                }

                ulong n = Volatile.Read(ref head->NextLevel);
                BucketNode* next = (BucketNode*)n;

                try
                {
                    // 对next节点获取PrevLock，因为我们要修改它的PreviousLevel
                    if (next != null && !next->TryAcquirePrevLock())
                    {
                        Thread.Sleep(0);
                        continue;
                    }

                    try
                    {
                        if (Interlocked.CompareExchange(ref _bucketHeads[index], head->NextLevel, h) == h)
                        {
                            node = head;
                            node->IsInBucket = false;
                            node->NextLevel = EmptyHandle;
                            if (next != null) {
                                next->PreviousLevel = EmptyHandle;
                            }
                            return true;
                        } else
                        {
                            Thread.Sleep(0);
                            continue;
                        }
                    }
                    finally
                    {
                        if (next != null) {
                            next->ReleasePrevLock();
                        }
                    }
                }
                finally
                {
                    head->ReleaseNextLock();
                }
            }
        }

        /// <summary>
        ///   BucketNode structure - specialized node for bucket linked lists Stored in main
        ///   allocation area (user-overwritable region)
        /// </summary>
        [StructLayout(LayoutKind.Explicit, Size = 40)]
        internal struct BucketNode
        {

            public const uint MAGIC_NUMBER = 0xBEEFCAFE; // Magic number for node integrity verification

            [FieldOffset(16)] internal Entry* EntryRef;     // Pointer to corresponding Entry
            [FieldOffset(28)] internal bool IsInBucket;     // Whether in bucket
            [FieldOffset(36)] internal int NextLock;        // 后继指针锁（控制NextLevel指针操作）

            // 双锁设计：分离前后指针操作
            [FieldOffset(32)] internal int PrevLock;        // 前驱指针锁（控制PreviousLevel指针操作）
            [FieldOffset(24)] internal uint Magic;          // Magic number verification

            [FieldOffset(0)]  internal ulong NextLevel;     // Bucket stack linked list: next pointer
            [FieldOffset(8)]  internal ulong PreviousLevel; // Bucket stack linked list: previous pointer

        }

        /// <summary>
        ///   BucketNode操作的静态方法集合
        /// </summary>
        private static class BucketNodeOperations
        {

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool IsNullOrEmpty(BucketNode* node)
            {
                return node == null || node->Magic != BucketNode.MAGIC_NUMBER;
            }

            #region Lock Operations

            // 前驱锁操作（控制PreviousLevel字段）
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool TryAcquirePrevLock(BucketNode* node)
            {
                if (node == null) {
                    return true;
                }

                int thread = Environment.CurrentManagedThreadId;
                return Interlocked.CompareExchange(ref node->PrevLock, thread, 0) == 0;
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static void AcquirePrevLock(BucketNode* node)
            {
                if (node == null) {
                    return;
                }

                int thread = Environment.CurrentManagedThreadId;
                if (Volatile.Read(ref node->PrevLock) != thread)
                {
                    while (Interlocked.CompareExchange(ref node->PrevLock, thread, 0) != 0) {
                        Thread.Sleep(0);
                    }
                }
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static void ReleasePrevLock(BucketNode* node)
            {
                if (node == null) {
                    return;
                }

                int thread = Environment.CurrentManagedThreadId;
                if (Volatile.Read(ref node->PrevLock) == thread) {
                    Volatile.Write(ref node->PrevLock, 0);
                }
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool IsPrevLockHeld(BucketNode* node) => node != null &&
                                                                   Volatile.Read(ref node->PrevLock) != 0;

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool IsPrevLockHeldByCurrentThread(BucketNode* node) => node != null &&
                                                                                  Volatile.Read(ref node->PrevLock) == Environment.CurrentManagedThreadId;

            // 后继锁操作（控制NextLevel字段）
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool TryAcquireNextLock(BucketNode* node)
            {
                if (node == null) {
                    return true;
                }

                int thread = Environment.CurrentManagedThreadId;
                return Interlocked.CompareExchange(ref node->NextLock, thread, 0) == 0;
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static void AcquireNextLock(BucketNode* node)
            {
                if (node == null) {
                    return;
                }

                int thread = Environment.CurrentManagedThreadId;
                if (Volatile.Read(ref node->NextLock) != thread)
                {
                    while (Interlocked.CompareExchange(ref node->NextLock, thread, 0) != 0) {
                        Thread.Sleep(0);
                    }
                }
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static void ReleaseNextLock(BucketNode* node)
            {
                if (node == null) {
                    return;
                }

                int thread = Environment.CurrentManagedThreadId;
                if (Volatile.Read(ref node->NextLock) == thread) {
                    Volatile.Write(ref node->NextLock, 0);
                }
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool IsNextLockHeld(BucketNode* node) => node != null &&
                                                                   Volatile.Read(ref node->NextLock) != 0;

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool IsNextLockHeldByCurrentThread(BucketNode* node) => node != null &&
                                                                                  Volatile.Read(ref node->NextLock) == Environment.CurrentManagedThreadId;

            // 双锁组合操作
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static bool TryAcquireBothLocks(BucketNode* node)
            {
                if (node == null) {
                    return true;
                }

                if (TryAcquirePrevLock(node))
                {
                    if (TryAcquireNextLock(node))
                    {
                        return true;
                    } else
                    {
                        ReleasePrevLock(node); // 回滚
                        return false;
                    }
                }
                return false;
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static void ReleaseBothLocks(BucketNode* node)
            {
                if (node == null) {
                    return;
                }

                ReleasePrevLock(node);
                ReleaseNextLock(node);
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public static void AcquireBothLocks(BucketNode* node)
            {
                if (node == null) {
                    return;
                }

                AcquirePrevLock(node);
                AcquireNextLock(node);
            }

            #endregion
        }

    }
}