#include <QApplication>
#include <QScrollArea>
#include <QTabWidget>
#include <QVBoxLayout>
#include <QWidget>

#include <memory>

/*
Creates a widget that contains two children: a green one with a fixed height,
and a red one that expands vertically, with a minimum height of zero.
*/
std::unique_ptr<QWidget> makeTab() {

    auto widget = std::make_unique<QWidget>();

    auto fixedHeightWidget = new QWidget(widget.get());
    fixedHeightWidget->setFixedHeight(100);
    fixedHeightWidget->setStyleSheet("QWidget { background-color: green; }");

    auto spacerWidget = new QWidget(widget.get());
    spacerWidget->setMinimumHeight(0);
    spacerWidget->setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::Expanding);
    spacerWidget->setStyleSheet("QWidget { background-color: red; }");

    auto layout = new QVBoxLayout(widget.get());
    layout->addWidget(fixedHeightWidget);
    layout->addWidget(spacerWidget);

    return widget;
}


/*
Creates a tab widget with n tabs, where each tab is constructed with makeTab()
*/
std::unique_ptr<QWidget> makeTabWidget(int tabCount) {
    auto widget = std::make_unique<QWidget>();

    auto tabWidget = new QTabWidget(widget.get());
    for (int i = 0; i < tabCount; ++i) {
        tabWidget->addTab(makeTab().release(), "Tab");
    }
    tabWidget->setTabBarAutoHide(true);

    auto layout = new QVBoxLayout(widget.get());
    layout->addWidget(tabWidget);

    return widget;

}

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

    // This scroll area does not allow the lone tab to be resized to its actual
    // minimum size, the height of the (invisible) tab bar is still added.
    QScrollArea singleTab;
    singleTab.setWidget(makeTabWidget(1).release());
    singleTab.setWidgetResizable(true);
    singleTab.show();

    // With a visible tab bar, the tabs can be resized to their expected
    // minimum size.
    QScrollArea doubleTab;
    doubleTab.setWidget(makeTabWidget(2).release());
    doubleTab.setWidgetResizable(true);
    doubleTab.show();

    return a.exec();
}