#include <QtCore/QCoreApplication>
#include <QStringList>
#include <QFile>

bool isBeginning(QFile& f, qint64 offset)
{
    qDebug("offset: 0x%x", offset);
    int size = f.size();
    int dataSize = size - offset;

    f.seek(offset - 12);
    QByteArray data = f.read(12);

    quint32* d = (quint32*)data.data();

    if(d[0] == d[1])
    {
        int dataSize2 = d[0] * d[0] * d[2] / 8;
        return (dataSize == dataSize2);
    }
    else
    {
        return false;
    }
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QStringList args = a.arguments();
    if(args.size() != 3)
    {
        qCritical("Usage: %s <infile.L15> <outfile.pgm>", argv[0]);
        return 1;
    }

    QString finame = args[1];
    QString foname = args[2];

    QFile fi(finame);
    QFile fo(foname);

    if(!fi.open(QFile::ReadOnly))
    {
        qCritical("Can't open file %s", qPrintable(finame));
        return 1;
    }
    if(!fo.open(QFile::WriteOnly))
    {
        fi.close();
        qCritical("Can't open file %s", qPrintable(foname));
        return 1;
    }

    qint64 size = fi.size();

    qDebug("File size: %ld", size);

    int k = 0;
    if(size>(11136*11136*2))
    {
        k = 11136;
    }
    else if(size>(2784*2784*2))
    {
        k = 2784;
    }

    qDebug("Data size: %ld", k*k*2);
    qDebug("k=%d", k);

    qint64 offset = 0;
    if(k>0)
    {
        if(isBeginning(fi, size - (k*k*2)))
        {
            offset = size - (k*k*2);
            qDebug("Found");
        }
    }

    if(offset==0)
    {
        for(qint64 i=0; i<size-20; i++)
        {
            if(isBeginning(fi, i))
            {
                offset = i;
                break;
            }
        }
    }

    if(offset==0)
    {
        fi.close();
        fo.close();
        qCritical("Header not found");
        return 1;
    }

    fi.seek(offset-12);
    QByteArray header = fi.read(16);
    quint32* headPtr = (quint32*)header.data();
    quint32 w = headPtr[0];
    quint32 h = headPtr[1];
    quint32 d = headPtr[2];
    Q_ASSERT(d==16);

    QString pgmHeader = QString("P5\n%1 %2\n65535\n").arg(w).arg(h);

    fo.write(qPrintable(pgmHeader));

    fi.seek(offset);
    while(offset < size)
    {
        QByteArray data = fi.read(1024);
        quint8* ptr = (quint8*)data.data();
        for(int i=0; i<data.size(); i+=2, ptr+=2)
        {
            quint8 t = ptr[0];
            ptr[0] = ptr[1];
            ptr[1] = t;
        }
        fo.write(data);
        offset += 1024;
    }

    fi.close();
    fo.close();

    return 0;
}