using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace MvvmScaffoldFrame48.DLL.SystemTools
{
    public sealed class LockFreeRingBuffer<T>
    {
        private readonly T[] _buffer;
        private readonly int _mask;
        private volatile int _readIndex;
        private volatile int _writeIndex;
        private readonly int _capacity;

        public LockFreeRingBuffer(int capacity)
        {
            // 容量必须是2的幂次方
            if (!IsPowerOfTwo(capacity))
                capacity = RoundUpToPowerOfTwo(capacity);

            _capacity = capacity;
            _mask = _capacity - 1;
            _buffer = new T[_capacity];
        }

        private static bool IsPowerOfTwo(int x)
        {
            return x > 0 && (x & (x - 1)) == 0;
        }

        private static int RoundUpToPowerOfTwo(int x)
        {
            if (x <= 1) return 1;
            x--;
            x |= x >> 1;
            x |= x >> 2;
            x |= x >> 4;
            x |= x >> 8;
            x |= x >> 16;
            return x + 1;
        }

        public bool TryEnqueue(T item)
        {
            int currentWriteIndex, nextWriteIndex, currentReadIndex;

            do
            {
                currentWriteIndex = _writeIndex;
                currentReadIndex = _readIndex;
                nextWriteIndex = (currentWriteIndex + 1) & _mask;

                // 检查是否已满
                if (nextWriteIndex == currentReadIndex)
                    return false;

            } while (Interlocked.CompareExchange(ref _writeIndex, nextWriteIndex, currentWriteIndex) != currentWriteIndex);

            // 设置值并更新发布标记
            _buffer[currentWriteIndex & _mask] = item;

            return true;
        }

        public bool TryDequeue(out T result)
        {
            result = default(T);
            int currentReadIndex, nextReadIndex, currentWriteIndex;

            do
            {
                currentReadIndex = _readIndex;
                currentWriteIndex = _writeIndex;

                // 检查是否为空
                if (currentReadIndex == currentWriteIndex)
                    return false;

                nextReadIndex = (currentReadIndex + 1) & _mask;

            } while (Interlocked.CompareExchange(ref _readIndex, nextReadIndex, currentReadIndex) != currentReadIndex);

            result = _buffer[currentReadIndex & _mask];
            _buffer[currentReadIndex & _mask] = default(T); // 防止内存泄漏

            return true;
        }

        public int Count
        {
            get
            {
                int read = _readIndex;
                int write = _writeIndex;
                return (write - read) & _mask;
            }
        }
    }
}