class FormattedLabel : public QLabel
{
    Q_OBJECT
public:
    using FormatCallback = std::function<QString(const QString&)>;

    FormattedLabel(const FormatCallback& format_callback = FormatCallback(), QWidget* parent = nullptr)
        : QLabel(parent), m_format_callback(format_callback) {}

    void set_format_callback(const FormatCallback& format_callback)
    {
        m_format_callback = format_callback;
        update_text();
    }
protected:
    void paintEvent(QPaintEvent* event) override
    {
        const QString& current_text = text();
        if (current_text != m_formatted_text)
        {
            m_plain_text = current_text;
            update_text();
        }

        QLabel::paintEvent(event);
    }
    void resizeEvent(QResizeEvent* event) override
    {
        QLabel::resizeEvent(event);
        const QString& current_text = text();
        if (current_text != m_formatted_text)
        {
            m_plain_text = current_text;
        }
        update_text();
    }
private:
    void update_text()
    {
        if (!m_format_callback)
        {
            return;
        }

        m_formatted_text = m_format_callback(m_plain_text);
        setText(m_formatted_text);
    }

    QString m_formatted_text;
    QString m_plain_text;
    FormatCallback m_format_callback;
};