// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Runtime.InteropServices;
 
namespace Windows.Win32.System.Com;
 
internal sealed unsafe class ComManagedStream : IStream.Interface, IManagedWrapper<IStream, ISequentialStream>
{
    private readonly Stream _dataStream;
 
    // To support seeking ahead of the stream length
    private long _virtualPosition = -1;
 
    internal ComManagedStream(Stream stream, bool makeSeekable = false)
    {
        if (makeSeekable && !stream.CanSeek)
        {
            // Copy to a memory stream so we can seek
            MemoryStream memoryStream = new();
            stream.CopyTo(memoryStream);
            _dataStream = memoryStream;
        }
        else
        {
            _dataStream = stream;
        }
    }
 
    private void ActualizeVirtualPosition()
    {
        if (_virtualPosition == -1)
            return;
 
        if (_virtualPosition > _dataStream.Length)
            _dataStream.SetLength(_virtualPosition);
 
        _dataStream.Position = _virtualPosition;
 
        _virtualPosition = -1;
    }
 
    public Stream GetDataStream() => _dataStream;
 
    HRESULT IStream.Interface.Clone(IStream** ppstm)
    {
        if (ppstm is null)
        {
            return HRESULT.E_POINTER;
        }
 
        // The cloned object should have the same current "position"
        *ppstm = ComHelpers.GetComPointer<IStream>(
            new ComManagedStream(_dataStream) { _virtualPosition = _virtualPosition });
 
        return HRESULT.S_OK;
    }
 
    HRESULT IStream.Interface.Commit(uint grfCommitFlags)
    {
        _dataStream.Flush();
 
        // Extend the length of the file if needed.
        ActualizeVirtualPosition();
        return HRESULT.S_OK;
    }
 
    HRESULT IStream.Interface.CopyTo(IStream* pstm, ulong cb, ulong* pcbRead, ulong* pcbWritten)
    {
        if (pstm is null)
        {
            return HRESULT.STG_E_INVALIDPOINTER;
        }
 
        using BufferScope<byte> buffer = new(4096);
 
        ulong remaining = cb;
        ulong totalWritten = 0;
        ulong totalRead = 0;
 
        fixed (byte* b = buffer)
        {
            while (remaining > 0)
            {
                uint read = remaining < (ulong)buffer.Length ? (uint)remaining : (uint)buffer.Length;
 
                ((IStream.Interface)this).Read(b, read, &read);
                remaining -= read;
                totalRead += read;
 
                if (read == 0)
                {
                    break;
                }
 
                uint written;
                pstm->Write(b, read, &written).ThrowOnFailure();
                totalWritten += written;
            }
        }
 
        if (pcbRead is not null)
            *pcbRead = totalRead;
 
        if (pcbWritten is not null)
            *pcbWritten = totalWritten;
 
        return HRESULT.S_OK;
    }
 
    HRESULT ISequentialStream.Interface.Read(void* pv, uint cb, uint* pcbRead)
    {
        if (pv is null)
        {
            return HRESULT.STG_E_INVALIDPOINTER;
        }
 
        ActualizeVirtualPosition();
 
        Span<byte> buffer = new(pv, checked((int)cb));
        int read = _dataStream.Read(buffer);
 
        if (pcbRead is not null)
            *pcbRead = (uint)read;
 
        return HRESULT.S_OK;
    }
 
    HRESULT IStream.Interface.Read(void* pv, uint cb, uint* pcbRead)
        => ((ISequentialStream.Interface)this).Read(pv, cb, pcbRead);
 
    HRESULT IStream.Interface.Seek(long dlibMove, SeekOrigin dwOrigin, ulong* plibNewPosition)
    {
        long position = _virtualPosition == -1 ? _dataStream.Position : _virtualPosition;
        long length = _dataStream.Length;
 
        switch (dwOrigin)
        {
            case SeekOrigin.Begin:
                if (dlibMove <= length)
                {
                    _dataStream.Position = dlibMove;
                    _virtualPosition = -1;
                }
                else
                {
                    _virtualPosition = dlibMove;
                }
 
                break;
            case SeekOrigin.End:
                if (dlibMove <= 0)
                {
                    _dataStream.Position = length + dlibMove;
                    _virtualPosition = -1;
                }
                else
                {
                    _virtualPosition = length + dlibMove;
                }
 
                break;
            case SeekOrigin.Current:
                if (dlibMove + position <= length)
                {
                    _dataStream.Position = position + dlibMove;
                    _virtualPosition = -1;
                }
                else
                {
                    _virtualPosition = dlibMove + position;
                }
 
                break;
        }
 
        if (plibNewPosition is null)
            return HRESULT.S_OK;
 
        *plibNewPosition = _virtualPosition == -1 ? (ulong)_dataStream.Position : (ulong)_virtualPosition;
        return HRESULT.S_OK;
    }
 
    HRESULT IStream.Interface.SetSize(ulong libNewSize)
    {
        _dataStream.SetLength(checked((long)libNewSize));
        return HRESULT.S_OK;
    }
 
    HRESULT IStream.Interface.Stat(STATSTG* pstatstg, uint grfStatFlag)
    {
        if (pstatstg is null)
        {
            return HRESULT.STG_E_INVALIDPOINTER;
        }
 
        *pstatstg = new STATSTG
        {
            cbSize = (ulong)_dataStream.Length,
            type = (uint)STGTY.STGTY_STREAM,
 
            // Default read/write access is READ, which == 0
            grfMode = _dataStream.CanWrite
                ? _dataStream.CanRead
                    ? STGM.STGM_READWRITE
                    : STGM.STGM_WRITE
                : STGM.STGM_READ
        };
 
        if ((STATFLAG)grfStatFlag == STATFLAG.STATFLAG_DEFAULT)
        {
            // Caller wants a name
            pstatstg->pwcsName = (char*)Marshal.StringToCoTaskMemUni(_dataStream is FileStream fs ? fs.Name : _dataStream.ToString());
        }
 
        return HRESULT.S_OK;
    }
 
    /// Returns HRESULT.STG_E_INVALIDFUNCTION as a documented way to say we don't support locking
    HRESULT IStream.Interface.LockRegion(ulong libOffset, ulong cb, uint dwLockType) => HRESULT.STG_E_INVALIDFUNCTION;
 
    // We never report ourselves as Transacted, so we can just ignore this.
    HRESULT IStream.Interface.Revert() => HRESULT.S_OK;
 
    /// Returns HRESULT.STG_E_INVALIDFUNCTION as a documented way to say we don't support locking
    HRESULT IStream.Interface.UnlockRegion(ulong libOffset, ulong cb, uint dwLockType) => HRESULT.STG_E_INVALIDFUNCTION;
 
    HRESULT ISequentialStream.Interface.Write(void* pv, uint cb, uint* pcbWritten)
    {
        if (pv is null)
        {
            return HRESULT.STG_E_INVALIDPOINTER;
        }
 
        ActualizeVirtualPosition();
 
        ReadOnlySpan<byte> buffer = new(pv, checked((int)cb));
        _dataStream.Write(buffer);
 
        if (pcbWritten is not null)
            *pcbWritten = cb;
 
        return HRESULT.S_OK;
    }
 
    HRESULT IStream.Interface.Write(void* pv, uint cb, uint* pcbWritten)
        => ((ISequentialStream.Interface)this).Write(pv, cb, pcbWritten);
}