Method updateNavButtons

pj_widgets/src/DateRangePicker.cpp:778–824

}

void DualCalendarWidget::updateNavButtons() {
  int ln_y = left_year_, ln_m = left_month_;
  advanceMonth(ln_y, ln_m, 1);
  bool at_max = ln_y > left_max_year_ || (ln_y == left_max_year_ && ln_m > left_max_month_);
  bool at_right = ln_y > right_year_ || (ln_y == right_year_ && ln_m >= right_month_);
  left_next_->setEnabled(!at_max && !at_right);

  int rp_y = right_year_, rp_m = right_month_;
  advanceMonth(rp_y, rp_m, -1);
  const bool currently_ge_min =
      right_year_ > right_min_year_ || (right_year_ == right_min_year_ && right_month_ >= right_min_month_);
  bool at_minimum =
      currently_ge_min && (rp_y < right_min_year_ || (rp_y == right_min_year_ && rp_m < right_min_month_));
  bool at_left = rp_y < left_year_ || (rp_y == left_year_ && rp_m <= left_month_);
  right_prev_->setEnabled(!at_minimum && !at_left);

  left_prev_->setEnabled(true);
  right_next_->setEnabled(true);

  // Direction hint: color the arrow text green/red when clicking it would
  // reveal the start/end date (currently outside both calendars' views).
  const int from_l = monthCmp(range_from_, left_year_, left_month_);
  const int from_r = monthCmp(range_from_, right_year_, right_month_);
  const int to_l = monthCmp(range_to_, left_year_, left_month_);
  const int to_r = monthCmp(range_to_, right_year_, right_month_);

  const bool from_before_l = from_l < 0;
  const bool from_in_gap = from_l > 0 && from_r < 0;
  const bool from_after_r = from_r > 0;
  const bool to_before_l = to_l < 0;
  const bool to_in_gap = to_l > 0 && to_r < 0;
  const bool to_after_r = to_r > 0;

  // Direction hint: recolor the chevron green/red when clicking it would reveal the
  // start/end date (currently outside both calendars' views); resting state is the
  // theme ink. The flat-button stylesheet set in the ctor is left untouched.
  const QColor ink = pickerTokens().text;
  auto apply_hint = [ink](QPushButton* btn, bool left, bool hint_from, bool hint_to) {
    const QColor c = hint_from ? kFromHintColor : (hint_to ? kToHintColor : ink);
    btn->setIcon(renderChevronIcon(left, c, kNavChevronPx));
  };

  apply_hint(left_prev_, /*left=*/true, from_before_l, to_before_l);
  apply_hint(left_next_, /*left=*/false, from_in_gap, to_in_gap);
  apply_hint(right_prev_, /*left=*/true, from_in_gap, to_in_gap);
  apply_hint(right_next_, /*left=*/false, from_after_r, to_after_r);
}

void DualCalendarWidget::onDateClicked(const QDate& date) {
  if (!selecting_) {