#include <QApplication>

#include <QTextDocument>
#include <QTextCursor>
#include <QFontComboBox>

#include <QPainter>

#include <QFrame>
#include <QGridLayout>
#include <QSlider>
#include <QLabel>

#include <QResizeEvent>

class TextWidget: public QWidget
{
  Q_OBJECT
public:
  TextWidget(QWidget *parent = 0): QWidget(parent), scale(1)
  {
    reset(new QTextDocument);
    doc->setDefaultFont(QFont("Calibri", 9));
    doc->setPlainText("viele Expeditionen seit seiner Gründung");
  }

  QTextDocument* document(void) { return doc.data(); }
  void reset(QTextDocument *d)
  {
    doc.reset(d);
    connect(d, &QTextDocument::contentsChanged, this, [this]() { update(); });
  }
  void zoom(qreal z)
  {
    scale = z;
    doc->setTextWidth(width() / scale);
    update();
  }

  virtual QSize sizeHint() const
  { return QSize(512, 128); }

protected:
  virtual void paintEvent(QPaintEvent *ev)
  {
    QPainter painter(this);
    painter.scale(scale, scale);
    doc->drawContents(&painter, QRect(0, 0, width() / scale, height() / scale));
  }
  virtual void resizeEvent(QResizeEvent *ev)
  {
    QWidget::resizeEvent(ev);
    if(ev) doc->setTextWidth(ev->size().width() / scale);
  }
private:
  QScopedPointer<QTextDocument> doc;
  qreal scale;
};

void findSizes(const QFont &font, QComboBox *sizeCombo)
{
  QFontDatabase fontDatabase;
  QString currentSize = sizeCombo->currentText();

  {
    const QSignalBlocker blocker(sizeCombo);
    // sizeCombo signals are now blocked until end of scope
    sizeCombo->clear();

    int size;
    if (fontDatabase.isSmoothlyScalable(font.family(), fontDatabase.styleString(font))) {
      foreach (size, QFontDatabase::standardSizes()) {
        sizeCombo->addItem(QVariant(size).toString());
        sizeCombo->setEditable(true);
      }

    } else {
      foreach (size, fontDatabase.smoothSizes(font.family(), fontDatabase.styleString(font))) {
        sizeCombo->addItem(QVariant(size).toString());
        sizeCombo->setEditable(false);
      }
    }
  }

  int sizeIndex = sizeCombo->findText(currentSize);

  if(sizeIndex == -1)
    sizeCombo->setCurrentIndex(qMax(0, sizeCombo->count() / 3));
  else
    sizeCombo->setCurrentIndex(sizeIndex);
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QFrame view;
    QGridLayout *pL;
    QSlider *pSl;
    QLabel *pLbl;
    QFontComboBox *pFontCombo;
    QComboBox *pSizeCombo;
    TextWidget *pTextWidget;
    view.setLayout(pL = new QGridLayout);
    pL->addWidget(pSl = new QSlider(Qt::Horizontal), 0, 0);
    pSl->setRange(1, 2048);
    pL->addWidget(pLbl = new QLabel, 0, 1);
    pL->addWidget(pFontCombo = new QFontComboBox, 0, 2);
    pL->addWidget(pSizeCombo = new QComboBox, 0, 3);
    pL->addWidget(pTextWidget = new TextWidget, 1, 0, 1, 4);
    QFont f = pTextWidget->document()->defaultFont();
    pFontCombo->setCurrentFont(f);
    findSizes(f, pSizeCombo);
    pSizeCombo->setCurrentText(QString::number(f.pointSize()));

    QObject::connect(pFontCombo, &QFontComboBox::currentFontChanged,
                     pTextWidget, [pTextWidget, pSizeCombo](const QFont &f)
    {
      findSizes(f, pSizeCombo);
      QTextCursor cursor(pTextWidget->document());
      cursor.select(QTextCursor::Document);
      QTextCharFormat fmt = cursor.charFormat();
      fmt.setFontFamily(f.family());
      cursor.setCharFormat(fmt);
    });

    QObject::connect(pSizeCombo, &QComboBox::currentTextChanged,
                     pTextWidget, [pTextWidget](const QString &s)
    {
      QTextCursor cursor(pTextWidget->document());
      cursor.select(QTextCursor::Document);
      QTextCharFormat fmt = cursor.charFormat();
      bool ok = false;
      if(s.toDouble(&ok) > 0 && ok)
      {
        fmt.setFontPointSize(s.toDouble());
        cursor.setCharFormat(fmt);
      }
    });


    QObject::connect(pSl, &QSlider::valueChanged,
                     pLbl, [pLbl, pTextWidget, &view](int val)
    {
      int dpix = view.logicalDpiX();
      int dpiy = view.logicalDpiY();
      pLbl->setText(QString("zoom: %1%; dpi: %2")
                    .arg(val).arg((dpix + dpiy) / 2));
      pTextWidget->zoom(val / 100.);
    });

    pSl->setValue(300);
    view.show();

    return a.exec();
}

#include "main.moc"