using System;
using System.Runtime.InteropServices;
using OpenTK.Graphics.OpenGL;
using Ryujinx.Common.Logging;
using Ryujinx.Graphics.GAL;
using Ryujinx.Graphics.OpenGL.Image;

namespace Ryujinx.Graphics.OpenGL
{
    class PersistentBuffers : IDisposable
    {
        private PersistentBuffer _main = new PersistentBuffer();
        private PersistentBuffer _background = new PersistentBuffer();

        public PersistentBuffer Default => BackgroundContextWorker.InBackground ? _background : _main;

        public void Dispose()
        {
            _main?.Dispose();
            _background?.Dispose();
        }
    }

    class PersistentBuffer : IDisposable
    {
        private IntPtr _bufferMap;
        private int _copyBufferHandle;
        private int _copyBufferSize;

        private void EnsureBuffer(int requiredSize)
        {
            if (_copyBufferSize < requiredSize && _copyBufferHandle != 0)
            {
                GL.DeleteBuffer(_copyBufferHandle);

                _copyBufferHandle = 0;
            }

            if (_copyBufferHandle == 0)
            {
                _copyBufferHandle = GL.GenBuffer();
                _copyBufferSize = requiredSize;

                GL.BindBuffer(BufferTarget.CopyWriteBuffer, _copyBufferHandle);
                GL.BufferStorage(BufferTarget.CopyWriteBuffer, requiredSize, IntPtr.Zero, BufferStorageFlags.MapReadBit | BufferStorageFlags.MapPersistentBit);

                _bufferMap = GL.MapBufferRange(BufferTarget.CopyWriteBuffer, IntPtr.Zero, requiredSize, BufferAccessMask.MapReadBit | BufferAccessMask.MapPersistentBit);
            }
        }

        private void Sync()
        {
            GL.MemoryBarrier(MemoryBarrierFlags.ClientMappedBufferBarrierBit);

            IntPtr sync = GL.FenceSync(SyncCondition.SyncGpuCommandsComplete, WaitSyncFlags.None);
            WaitSyncStatus syncResult = GL.ClientWaitSync(sync, ClientWaitSyncFlags.SyncFlushCommandsBit, 1000000000);

            if (syncResult == WaitSyncStatus.TimeoutExpired)
            {
                Logger.Error?.PrintMsg(LogClass.Gpu, $"Failed to sync persistent buffer state within 1000ms. Continuing...");
            }

            GL.DeleteSync(sync);
        }

        public byte[] GetTextureData(TextureView view)
        {
            int size = 0;

            for (int level = 0; level < view.Info.Levels; level++)
            {
                size += view.Info.GetMipSize(level);
            }

            EnsureBuffer(size);

            GL.BindBuffer(BufferTarget.PixelPackBuffer, _copyBufferHandle);

            view.WriteToPbo(0, false);

            GL.BindBuffer(BufferTarget.PixelPackBuffer, 0);

            byte[] data = new byte[size];

            Sync();

            Marshal.Copy(_bufferMap, data, 0, size);

            return data;
        }

        public byte[] GetBufferData(BufferHandle buffer, int offset, int size)
        {
            EnsureBuffer(size);

            GL.BindBuffer(BufferTarget.CopyReadBuffer, buffer.ToInt32());
            GL.BindBuffer(BufferTarget.CopyWriteBuffer, _copyBufferHandle);

            GL.CopyBufferSubData(BufferTarget.CopyReadBuffer, BufferTarget.CopyWriteBuffer, (IntPtr)offset, IntPtr.Zero, size);

            GL.BindBuffer(BufferTarget.CopyWriteBuffer, 0);

            byte[] data = new byte[size];

            Sync();

            Marshal.Copy(_bufferMap, data, 0, size);

            return data;
        }

        public void Dispose()
        {
            if (_copyBufferHandle != 0)
            {
                GL.DeleteBuffer(_copyBufferHandle);
            }
        }
    }
}