using System;
using System.IO;
using System.IO.MemoryMappedFiles;
using System.Runtime.InteropServices;
using System.Threading;
using GpuFanControl.MsiAfterburnerWrap.ShareMemoryStructs;

namespace GpuFanControl.MsiAfterburnerWrap
{
    internal class MsiAfterBurnControlWrap : IDisposable
    {
        //const
        private const string ShareMemoryName = "MACMSharedMemory";

        private const string MutexName = "Global\\Access_MACMSharedMemory";
        private const uint HeaderSignature = ('M' << 24 | ('A' << 16) | ('C' << 8) | ('M'));

        private MemoryMappedFile _hMapFile;
        private MemoryMappedViewStream _pMapAddr;

        private byte[] _bufSnap;

        public void Connect()
        {
            //connect , failure throws FileNotFoundException
            _hMapFile = MemoryMappedFile.OpenExisting(ShareMemoryName, MemoryMappedFileRights.FullControl);
            _pMapAddr = _hMapFile.CreateViewStream();
        }

        public void Disconnect()
        {
            _pMapAddr?.Close();
            _hMapFile?.Dispose();
        }

        public void Refresh()
        {
            using (var m = new Mutex(false, MutexName))
            {
                m.WaitOne();

                var lenHeader = Marshal.SizeOf(typeof(MACM_SHARED_MEMORY_HEADER));
                var bufHeader = new byte[lenHeader];

                _pMapAddr.Seek(0, SeekOrigin.Begin);
                _pMapAddr.Read(bufHeader, 0, lenHeader);

                var stHeader = ByteArrayToStruct<MACM_SHARED_MEMORY_HEADER>(bufHeader);
                if (stHeader.Signature == HeaderSignature)
                {
                    var lenSnap = stHeader.HeaderSize + stHeader.GpuEntryCount * stHeader.GpuEntrySize;

                    var bufSnap = new byte[lenSnap];

                    _pMapAddr.Seek(0, SeekOrigin.Begin);
                    _pMapAddr.Read(bufSnap, 0, (int)lenSnap);
                    _bufSnap = bufSnap;
                }
                m.ReleaseMutex();
            }
        }

        public void Commit()
        {
            using (var m = new Mutex(false, MutexName))
            {
                m.WaitOne();

                _pMapAddr.Seek(0, SeekOrigin.Begin);
                _pMapAddr.Write(_bufSnap, 0, _bufSnap.Length);
                _pMapAddr.Flush();

                _pMapAddr.Seek(0, SeekOrigin.Begin);
                var header = ByteArrayToStruct<MACM_SHARED_MEMORY_HEADER>(_bufSnap);
                header.Command = MACM_SHARED_MEMORY_COMMAND.FLUSH;
                StructToByteArray(header, _bufSnap);

                _pMapAddr.Seek(0, SeekOrigin.Begin);
                _pMapAddr.Write(_bufSnap, 0, _bufSnap.Length);
                _pMapAddr.Flush();

                m.ReleaseMutex();
            }

            Refresh();
        }

        public int GetNumberOfGpu()
        {
            var st = ByteArrayToStruct<MACM_SHARED_MEMORY_HEADER>(_bufSnap);
            return (int)st.GpuEntryCount;
        }

        public MACM_SHARED_MEMORY_GPU_ENTRY? GetGpuEntry(int index, out string error)
        {
            var header = ByteArrayToStruct<MACM_SHARED_MEMORY_HEADER>(_bufSnap);
            if (index > header.GpuEntryCount || index < 0)
            {
                error = "index out of range";
                return null;
            }
            var entry = ByteArrayToStruct<MACM_SHARED_MEMORY_GPU_ENTRY>(_bufSnap, (int)header.HeaderSize + index * (int)header.GpuEntrySize);

            error = null;
            return entry;
        }

        public string SetGpuEntry(MACM_SHARED_MEMORY_GPU_ENTRY entry, int index, bool flush = false)
        {
            var header = ByteArrayToStruct<MACM_SHARED_MEMORY_HEADER>(_bufSnap);
            if (index > header.GpuEntryCount || index < 0) return "index out of range";

            StructToByteArray(entry, _bufSnap, (int)(header.HeaderSize + index * header.GpuEntrySize));

            if (flush) Commit();

            return null;
        }

        private T ByteArrayToStruct<T>(byte[] bytes, int offset = 0)
        {
            GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);
            T stuff;
            try
            {
                stuff = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject() + offset, typeof(T));
            }
            finally
            {
                handle.Free();
            }
            return stuff;
        }

        private static void StructToByteArray<T>(T str, byte[] snap, int offset = 0)
        {
            var h = default(GCHandle);

            try
            {
                h = GCHandle.Alloc(snap, GCHandleType.Pinned);

                Marshal.StructureToPtr<T>(str, h.AddrOfPinnedObject() + offset, false);
            }
            finally
            {
                if (h.IsAllocated)
                {
                    h.Free();
                }
            }
        }

        public void Dispose()
        {
            Disconnect();
        }
    }
}