#pragma region IInitializeWithStream

// Initializes the thumbnail handler with a stream.
IFACEMETHODIMP ThumbnailProvider::Initialize(IStream *pStream, DWORD grfMode)
{
    std::ofstream st;
    // A handler instance should be initialized only once in its lifetime.
    HRESULT hr = HRESULT_FROM_WIN32(ERROR_ALREADY_INITIALIZED);
    if (m_pStream == NULL)
    {
        // Take a reference to the stream if it has not been initialized yet.
        hr = pStream->QueryInterface(&m_pStream);
    }
    return hr;
}

#pragma endregion


#pragma region IThumbnailProvider

// Gets a thumbnail image and alpha type. The GetThumbnail is called with the
// largest desired size of the image, in pixels. Although the parameter is
// called cx, this is used as the maximum size of both the x and y dimensions.
// If the retrieved thumbnail is not square, then the longer axis is limited
// by cx and the aspect ratio of the original image respected. On exit,
// GetThumbnail provides a handle to the retrieved image. It also provides a
// value that indicates the color at of the image and whether it has
// valid alpha ination.
IFACEMETHODIMP ThumbnailProvider::GetThumbnail(UINT cx, HBITMAP *phbmp,
    WTS_ALPHATYPE *pdwAlpha) {
    stripImage(m_pStream, phbmp, cx);

    *pdwAlpha = WTSAT_UNKNOWN;

    return S_OK;
}

#pragma endregion
#pragma region Helper Functions

// The PNG signature is 137 80 78 71 13 10 26 10. This does not make sense to do backward. I will do it forward.
void ThumbnailProvider::stripImage(IStream *stream, HBITMAP *phbmp, UINT cx) {

    unsigned long numBytes = 0;
    unsigned long *numBytesPtr = &numBytes;
    uint8_t b = 0;
    uint8_t *buff = &b;
    byte vals[8] = { 0 };
    STATSTG stt = {};
    STATSTG *stat = &stt;
    DWORD temp = 1;
    stream->Stat(stat, temp);
    unsigned long long length = stat->cbSize.QuadPart;
    unsigned long long i;
    for (i = 0; i<length; i++) {
        stream->Read(buff, 1, numBytesPtr);

        if (*buff == 137) {
            vals[0] = 1;
        }
        else if (*buff == 80 && vals[0]) {
            vals[1] = 1;
        }
        else if (*buff == 78 && vals[1]) {
            vals[2] = 1;
        }
        else if (*buff == 71 && vals[2]) {
            vals[3] = 1;
        }
        else if (*buff == 13  && vals[3]) {
            vals[4] = 1;
        }
        else if (*buff == 10  && vals[4] && !vals[5]) {
            vals[5] = 1;
        }
        else if (*buff == 26  && vals[5]) {
            vals[6] = 1;
        }
        else if (*buff == 10 && vals[6]) {
            vals[7] = 1;
            i -= 8;
            break;
        }
        else {
            memset(vals, 0, 8 * sizeof(vals[0]));
        }
    }
    if (vals[7]) {
        LARGE_INTEGER t;
        t.QuadPart = i;
        stream->Seek(t, STREAM_SEEK_SET, NULL);
        char * imgbuff = (char *)malloc(length-i);
        stream->Read(imgbuff, length-i, numBytesPtr);
        IStream *istrm = NULL;
        HGLOBAL glob = ::GlobalAlloc(GHND, length - i);
        LPBYTE bt = (LPBYTE)::GlobalLock(glob);
        ::GlobalUnlock(glob);
        if (SUCCEEDED(::CreateStreamOnHGlobal(glob, FALSE, &istrm))) {
            istrm->Write(imgbuff, length - i, numBytesPtr);
            CImage *img = NULL;
            img->Load(istrm);
            *phbmp = (HBITMAP)img->Detach();
        }
        //istrm->Release();
        GlobalFree(glob);

    }
}
#pragma endregion