QSyntaxHighlighter::highlightBlock highlights previous and current block

added

Implementation:

CustomHighlighter::CustomHighlighter(QTextDocument *parent) : QSyntaxHighlighter(parent) {
}
 
void CustomHighlighter::setHighlighterFormat(const QTextCharFormat &format) {
    this->format = format;
}
 
void CustomHighlighter::highlightBlock(const QString &text) {
//    if(text.isEmpty() || currentBlockState() == 1)
//        return;
    setFormat(0, text.length(), format);
//    setCurrentBlockState(1);
}
 
Logger::Logger(QWidget *parent) : QPlainTextEdit(parent) {
    setMaximumBlockCount(50);
    highlighter = new CustomHighlighter(document());
}
 
Logger::~Logger() {
    delete highlighter;
}
 
void Logger::setFormat(const QTextCharFormat &format) {
    highlighter->setHighlighterFormat(format);
}

Next is a timer slot, just for example:

QTextCharFormat format;
format.setFontWeight(250);
int x = random() % 3;
switch(x) {
case 0:
    format.setForeground(Qt::red);
    break;
case 1:
    format.setForeground(Qt::green);
    break;
case 2:
    format.setForeground(Qt::blue);
    break;
}
 
logger->setFormat(format);
QDateTime date = QDateTime::currentDateTime();
logger->appendPlainText(date.toString() + "\n");

This works fine. But if new line character is removed both current appended and previous line (block) are highlighted.

added

So I added enum to check block states:

 enum { FORMATTED = 1, LAST = 2 };

Then made changes in highlightBlock:

void CustomHighlighter::highlightBlock(const QString &text) {
    if(text.isEmpty() || currentBlockState() == LAST)
        return;
    if(currentBlockState() == FORMATTED) {
        setFormat(0, text.length(), previousFormat);
        setCurrentBlockState(LAST);
    } else {
        setFormat(0, text.length(), format);
        previousFormat = format;
        setCurrentBlockState(FORMATTED);
    }
}

This has one problem. After maximum blocks are appended the top most block "looses" format.
But anyway it seems that I am overdoing it. And why is formatted text returned to highlightBlock?

added

Okay, this works:

void CustomHighlighter::highlightBlock(const QString &text) {
    if(text.isEmpty())
        return;
    int start = 0;
    if(currentBlockState() == LAST) {
        BlockFormat block = queue.dequeue();
        QTextCharFormat lastFormat = block.first;
        int length = block.second;
        setFormat(start, length, lastFormat);
    }
    else if(currentBlockState() == FORMATTED) {
        setFormat(start, text.length(), previousFormat);
        setCurrentBlockState(LAST);
        queue.enqueue(BlockFormat(format, text.length()));
    } else {
        setFormat(start, text.length(), format);
        previousFormat = format;
        setCurrentBlockState(FORMATTED);
    }
}

Where BlockFormat is:

typedef QPair<QTextCharFormat, int> BlockFormat;

Question is same, am I overdoing it? Is this the simplest solution?