/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the TGA plugin in the Qt ImageFormats module.
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** ensure the GNU Lesser General Public License version 3 requirements
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****************************************************************************/

#include "qtgafile.h"

#include <QtCore/QIODevice>
#include <QtCore/QDebug>
#include <QtCore/QDateTime>
#include <QtGui/QImageIOHandler>

struct TgaReader
{
    Q_DISABLE_COPY(TgaReader)

    TgaReader() = default;

    virtual ~TgaReader() {}
    virtual QRgb operator()(QIODevice *s) const = 0;
};

struct Tga16Reader : public TgaReader
{
    ~Tga16Reader() {}
    QRgb operator()(QIODevice *s) const override
    {
        char ch1, ch2;
        if (s->getChar(&ch1) && s->getChar(&ch2)) {
            quint16 d = (int(ch1) & 0xFF) | ((int(ch2) & 0xFF) << 8);
            QRgb result = (d & 0x8000) ? 0xFF000000 : 0x00000000;
            result |= ((d & 0x7C00) << 6) | ((d & 0x03E0) << 3) | (d & 0x001F);
            return result;
        } else {
            return 0;
        }
    }
};

struct Tga24Reader : public TgaReader
{
    QRgb operator()(QIODevice *s) const override
    {
        char r, g, b;
        if (s->getChar(&b) && s->getChar(&g) && s->getChar(&r))
            return qRgb(uchar(r), uchar(g), uchar(b));
        else
            return 0;
    }
};

struct Tga32Reader : public TgaReader
{
    QRgb operator()(QIODevice *s) const override
    {
        char r, g, b, a;
        if (s->getChar(&b) && s->getChar(&g) && s->getChar(&r) && s->getChar(&a))
            return qRgba(uchar(r), uchar(g), uchar(b), uchar(a));
        else
            return 0;
    }
};

/*!
    \class QTgaFile
    \since 4.8
    \internal

    File data container for a TrueVision Graphics format file.

    Format is as described here:
    http://local.wasp.uwa.edu.au/~pbourke/dataformats/tga/
    http://netghost.narod.ru/gff2/graphics/summary/tga.htm

    Usage is:
    \code
    QTgaFile tga(myFile);
    QImage tgaImage;
    if (tga.isValid())
        tgaImage = tga.readImage();
    \endcode

    The class is designed to handle sequential and non-sequential
    sources, so during construction the mHeader is read.  Then during
    the readImage() call the rest of the data is read.

    After passing myFile to the constructor, if the QIODevice *myFile
    is read, or has seek() called, the results are undefined - so don't
    do that.
*/

/*!
    Construct a new QTgaFile object getting data from \a device.

    The object does not take ownership of the \a device, but until the
    object is destroyed do not do any non-const operations, eg seek or
    read on the device.
*/
QTgaFile::QTgaFile(QIODevice *device)
    : mDevice(device)
{
    ::memset(mHeader, 0, HeaderSize);
    if (!mDevice->isReadable())
    {
        mErrorMessage = tr("Could not read image data");
        return;
    }
    if (mDevice->isSequential())
    {
        mErrorMessage = tr("Sequential device (eg socket) for image read not supported");
        return;
    }
    if (!mDevice->seek(0))
    {
        mErrorMessage = tr("Seek file/device for image read failed");
        return;
    }
    if (device->read(reinterpret_cast<char*>(mHeader), HeaderSize) != HeaderSize) {
        mErrorMessage = tr("Image header read failed");
        return;
    }
    if (mHeader[ImageType] != 2)
    {
        // TODO: should support other image types
        mErrorMessage = tr("Image type not supported");
        return;
    }
    int bitsPerPixel = mHeader[PixelDepth];
    bool validDepth = (bitsPerPixel == 16 || bitsPerPixel == 24 || bitsPerPixel == 32);
    if (!validDepth)
    {
        mErrorMessage = tr("Image depth not valid");
        return;
    }
    if (quint64(width()) * quint64(height()) > (8192 * 8192))
    {
        mErrorMessage = tr("Image size exceeds limit");
        return;
    }
    int curPos = mDevice->pos();
    int fileBytes = mDevice->size();
    if (!mDevice->seek(fileBytes - FooterSize))
    {
        mErrorMessage = tr("Could not seek to image read footer");
        return;
    }
    char footer[FooterSize];
    if (mDevice->read(reinterpret_cast<char*>(footer), FooterSize) != FooterSize) {
        mErrorMessage = tr("Could not read footer");
    }
    if (qstrncmp(&footer[SignatureOffset], "TRUEVISION-XFILE", 16) != 0)
    {
        mErrorMessage = tr("Image type (non-TrueVision 2.0) not supported");
    }
    if (!mDevice->seek(curPos))
    {
        mErrorMessage = tr("Could not reset to read data");
    }
}

/*!
    \internal
    Destroy the device, recovering any resources.
*/
QTgaFile::~QTgaFile()
{
}

/*!
    \internal
    Reads an image file from the QTgaFile's device, and returns it.

    This method seeks to the absolute position of the image data in the file,
    so no assumptions are made about where the devices read pointer is when this
    method is called.  For this reason only random access devices are supported.

    If the constructor completed successfully, such that isValid() returns true,
    then this method is likely to succeed, unless the file is somehow corrupted.

    In the case that the read fails, the QImage returned will be null, such that
    QImage::isNull() will be true.
*/
QImage QTgaFile::readImage()
{
    if (!isValid())
        return QImage();

    int offset = mHeader[IdLength];  // Mostly always zero

    // Even in TrueColor files a color palette may be present so we have to check it here
    // even we only support image type 2 (= uncompressed true-color image)
    if (mHeader[ColorMapType] == 1) {
        int cmapDepth = mHeader[CMapDepth];
        if (cmapDepth == 15)    // 15 bit is stored as 16 bit + ignoring the highest bit (no alpha)
            cmapDepth = 16;
        if (cmapDepth != 16 && cmapDepth != 24 && cmapDepth != 32) {
            mErrorMessage = tr("Invalid color map depth (%1)").arg(cmapDepth);
            return {};
        }
        offset += littleEndianInt(&mHeader[CMapLength]) * cmapDepth / 8;
    }

    mDevice->seek(HeaderSize + offset);

    char dummy;
    for (int i = 0; i < offset; ++i)
        mDevice->getChar(&dummy);

    int bitsPerPixel = mHeader[PixelDepth];
    int imageWidth = width();
    int imageHeight = height();

    unsigned char desc = mHeader[ImageDescriptor];
    //unsigned char xCorner = desc & 0x10; // 0 = left, 1 = right
    unsigned char yCorner = desc & 0x20; // 0 = lower, 1 = upper

    QImage im;
    if (!QImageIOHandler::allocateImage(QSize(imageWidth, imageHeight), QImage::Format_ARGB32, &im))
        return QImage();
    TgaReader *reader = 0;
    if (bitsPerPixel == 16)
        reader = new Tga16Reader();
    else if (bitsPerPixel == 24)
        reader = new Tga24Reader();
    else if (bitsPerPixel == 32)
        reader = new Tga32Reader();
    else
        return QImage();
    TgaReader &read = *reader;

    // For now only deal with yCorner, since no one uses xCorner == 1
    // Also this is upside down, since Qt has the origin flipped
    if (yCorner)
    {
        for (int y = 0; y < imageHeight; ++y)
            for (int x = 0; x < imageWidth; ++x)
                im.setPixel(x, y, read(mDevice));
    }
    else
    {
        for (int y = imageHeight - 1; y >= 0; --y)
            for (int x = 0; x < imageWidth; ++x)
                im.setPixel(x, y, read(mDevice));
    }

    delete reader;

    // TODO: add processing of TGA extension information - ie TGA 2.0 files
    return im;
}
