using Ryujinx.Graphics.GAL;
using SharpMetal.Metal;
using System;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;
using System.Threading;

namespace Ryujinx.Graphics.Metal
{
    [SupportedOSPlatform("macos")]
    public class BufferHolder : IDisposable
    {
        public int Size { get; }

        private readonly IntPtr _map;
        private readonly MetalRenderer _renderer;
        private readonly Pipeline _pipeline;

        private readonly MultiFenceHolder _waitable;
        private readonly Auto<DisposableBuffer> _buffer;

        private readonly ReaderWriterLockSlim _flushLock;
        private FenceHolder _flushFence;
        private int _flushWaiting;

        public BufferHolder(MetalRenderer renderer, Pipeline pipeline, MTLBuffer buffer, int size)
        {
            _renderer = renderer;
            _pipeline = pipeline;
            _map = buffer.Contents;
            _waitable = new MultiFenceHolder(size);
            _buffer = new Auto<DisposableBuffer>(new(buffer), _waitable);

            _flushLock = new ReaderWriterLockSlim();

            Size = size;
        }

        public Auto<DisposableBuffer> GetBuffer()
        {
            return _buffer;
        }

        public Auto<DisposableBuffer> GetBuffer(bool isWrite)
        {
            if (isWrite)
            {
                SignalWrite(0, Size);
            }

            return _buffer;
        }

        public Auto<DisposableBuffer> GetBuffer(int offset, int size, bool isWrite)
        {
            if (isWrite)
            {
                SignalWrite(offset, size);
            }

            return _buffer;
        }

        public void SignalWrite(int offset, int size)
        {
            if (offset == 0 && size == Size)
            {
                // TODO: Cache converted buffers
            }
            else
            {
                // TODO: Cache converted buffers
            }
        }

        private void ClearFlushFence()
        {
            // Assumes _flushLock is held as writer.

            if (_flushFence != null)
            {
                if (_flushWaiting == 0)
                {
                    _flushFence.Put();
                }

                _flushFence = null;
            }
        }

        private void WaitForFlushFence()
        {
            if (_flushFence == null)
            {
                return;
            }

            // If storage has changed, make sure the fence has been reached so that the data is in place.
            _flushLock.ExitReadLock();
            _flushLock.EnterWriteLock();

            if (_flushFence != null)
            {
                var fence = _flushFence;
                Interlocked.Increment(ref _flushWaiting);

                // Don't wait in the lock.

                _flushLock.ExitWriteLock();

                fence.Wait();

                _flushLock.EnterWriteLock();

                if (Interlocked.Decrement(ref _flushWaiting) == 0)
                {
                    fence.Put();
                }

                _flushFence = null;
            }

            // Assumes the _flushLock is held as reader, returns in same state.
            _flushLock.ExitWriteLock();
            _flushLock.EnterReadLock();
        }

        public PinnedSpan<byte> GetData(int offset, int size)
        {
            _flushLock.EnterReadLock();

            WaitForFlushFence();

            Span<byte> result;

            if (_map != IntPtr.Zero)
            {
                result = GetDataStorage(offset, size);

                // Need to be careful here, the buffer can't be unmapped while the data is being used.
                _buffer.IncrementReferenceCount();

                _flushLock.ExitReadLock();

                return PinnedSpan<byte>.UnsafeFromSpan(result, _buffer.DecrementReferenceCount);
            }

            throw new InvalidOperationException("The buffer is not mapped");
        }

        public unsafe Span<byte> GetDataStorage(int offset, int size)
        {
            int mappingSize = Math.Min(size, Size - offset);

            if (_map != IntPtr.Zero)
            {
                return new Span<byte>((void*)(_map + offset), mappingSize);
            }

            throw new InvalidOperationException("The buffer is not mapped.");
        }

        public unsafe void SetData(int offset, ReadOnlySpan<byte> data, CommandBufferScoped? cbs = null, Action endRenderPass = null, bool allowCbsWait = true)
        {
            int dataSize = Math.Min(data.Length, Size - offset);
            if (dataSize == 0)
            {
                return;
            }

            if (_map != IntPtr.Zero)
            {
                // If persistently mapped, set the data directly if the buffer is not currently in use.
                bool isRented = _buffer.HasRentedCommandBufferDependency(_renderer.CommandBufferPool);

                // If the buffer is rented, take a little more time and check if the use overlaps this handle.
                bool needsFlush = isRented && _waitable.IsBufferRangeInUse(offset, dataSize, false);

                if (!needsFlush)
                {
                    WaitForFences(offset, dataSize);

                    data[..dataSize].CopyTo(new Span<byte>((void*)(_map + offset), dataSize));

                    SignalWrite(offset, dataSize);

                    return;
                }
            }

            if (allowCbsWait)
            {
                _renderer.BufferManager.StagingBuffer.PushData(_renderer.CommandBufferPool, cbs, endRenderPass, this, offset, data);
            }
            else
            {
                bool rentCbs = cbs == null;
                if (rentCbs)
                {
                    cbs = _renderer.CommandBufferPool.Rent();
                }

                if (!_renderer.BufferManager.StagingBuffer.TryPushData(cbs.Value, endRenderPass, this, offset, data))
                {
                    // Need to do a slow upload.
                    BufferHolder srcHolder = _renderer.BufferManager.Create(dataSize);
                    srcHolder.SetDataUnchecked(0, data);

                    var srcBuffer = srcHolder.GetBuffer();
                    var dstBuffer = this.GetBuffer(true);

                    Copy(_pipeline, cbs.Value, srcBuffer, dstBuffer, 0, offset, dataSize);

                    srcHolder.Dispose();
                }

                if (rentCbs)
                {
                    cbs.Value.Dispose();
                }
            }
        }

        public unsafe void SetDataUnchecked(int offset, ReadOnlySpan<byte> data)
        {
            int dataSize = Math.Min(data.Length, Size - offset);
            if (dataSize == 0)
            {
                return;
            }

            if (_map != IntPtr.Zero)
            {
                data[..dataSize].CopyTo(new Span<byte>((void*)(_map + offset), dataSize));
            }
        }

        public void SetDataUnchecked<T>(int offset, ReadOnlySpan<T> data) where T : unmanaged
        {
            SetDataUnchecked(offset, MemoryMarshal.AsBytes(data));
        }

        public static void Copy(
            Pipeline pipeline,
            CommandBufferScoped cbs,
            Auto<DisposableBuffer> src,
            Auto<DisposableBuffer> dst,
            int srcOffset,
            int dstOffset,
            int size,
            bool registerSrcUsage = true)
        {
            var srcBuffer = registerSrcUsage ? src.Get(cbs, srcOffset, size).Value : src.GetUnsafe().Value;
            var dstbuffer = dst.Get(cbs, dstOffset, size, true).Value;

            pipeline.GetOrCreateBlitEncoder().CopyFromBuffer(
                srcBuffer,
                (ulong)srcOffset,
                dstbuffer,
                (ulong)dstOffset,
                (ulong)size);
        }

        public void WaitForFences()
        {
            _waitable.WaitForFences();
        }

        public void WaitForFences(int offset, int size)
        {
            _waitable.WaitForFences(offset, size);
        }

        public void Dispose()
        {
            _buffer.Dispose();

            _flushLock.EnterWriteLock();

            ClearFlushFence();

            _flushLock.ExitWriteLock();
        }
    }
}