Add free functions isHoliday() to check if the current day is a holiday

and previousDayHoliday() to check if previous day (relative to endtime) is a
holiday.

library/src/configuration.cpp

@@ -1838,3 +1838,42 @@ Configuration::getWeekDayWorkTime(QTime const &time, Qt::DayOfWeek dayOfWeek) {
 
     return value;
 }
+
+bool isHoliday(Configuration const &cfg, QDateTime const &t) {
+    int const weekDay = t.date().dayOfWeek();
+    for (auto[iter, rEnd] = cfg.WeekDays.equal_range(static_cast<Qt::DayOfWeek>(weekDay));
+         iter != rEnd;
+         ++iter) {
+
+        if (iter->second.m_type == ATBWeekDay::WeekDayType::HOLIDAY) {
+            QDate const &d = iter->second.m_date;
+            if (!d.isNull() && d.isValid()) {
+                if (t.date() == d) {
+                    return true;
+                }
+            }
+        }
+    }
+    return false;
+}
+
+bool previousDayHoliday(Configuration const &cfg, QDateTime const &t) {
+    int const weekDay = t.date().dayOfWeek();
+    int const previousWeekDay = (weekDay == static_cast<int>(Qt::Monday)) ?
+                static_cast<int>(Qt::Sunday) : (weekDay - 1);
+
+    for (auto[iter, rEnd] = cfg.WeekDays.equal_range(static_cast<Qt::DayOfWeek>(previousWeekDay));
+         iter != rEnd;
+         ++iter) {
+
+        if (iter->second.m_type == ATBWeekDay::WeekDayType::HOLIDAY) {
+            QDate const &d = iter->second.m_date;
+            if (!d.isNull() && d.isValid()) {
+                if (t.addDays(-1).date() == d) {
+                    return true;
+                }
+            }
+        }
+    }
+    return false;
+}