Improve period compution

chrono/period.cpp

@@ -35,14 +35,15 @@ namespace ChronoUtilities {
  */
 Period::Period(const DateTime &begin, const DateTime &end)
 {
-    m_years = end.year() - beg.year();
-    m_months = end.month() - beg.month();
-    m_days = end.day() - beg.day();
-    if (end.hour() < beg.hour()) {
-        --m_days;
+    m_years = end.year() - begin.year();
+    m_months = end.month() - begin.month();
+    if (m_months < 0) {
+        m_months += 12;
+        --m_years;
     }
+    m_days = end.day() - begin.day();
     if (m_days < 0) {
-        m_days += DateTime::daysInMonth(beg.year(), beg.month());
+        m_days += end.month() > 1 ? DateTime::daysInMonth(end.year(), end.month() - 1) : 31;
         --m_months;
     }
     if (m_months < 0) {
@@ -50,4 +51,33 @@ Period::Period(const DateTime &begin, const DateTime &end)
         --m_years;
     }
 }
+
+/*!
+ * \brief Adds the specified \a period to the specified date.
+ * \throws Might throw ConversionException if resulting DateTime would be out-of-range.
+ * \remarks
+ * - The order in which the years(), month() and days() are added matters. See the overall class description.
+ * - Since the accuracy of Period is only one day, the DateTime::timeOfDay() of the result always equals begin.timeOfDay().
+ */
+DateTime operator+(DateTime begin, Period period)
+{
+    auto year = begin.year() + period.years();
+    auto month = begin.month() + period.months();
+    if (month > 12) {
+        month -= 12;
+        ++year;
+    }
+    auto day = begin.day() + period.days();
+    const auto maxDays = DateTime::daysInMonth(year, month);
+    if (day > maxDays) {
+        day -= maxDays;
+        ++month;
+    }
+    if (month > 12) {
+        month -= 12;
+        ++year;
+    }
+    return DateTime::fromDate(year, month, day) + begin.timeOfDay();
+}
+
 } // namespace ChronoUtilities

chrono/period.h

@@ -41,6 +41,9 @@ inline int Period::days() const
 {
     return m_days;
 }
+
+DateTime operator+(DateTime begin, Period period);
+
 } // namespace ChronoUtilities
 
 #endif // CHRONO_UTILITIES_PERIOD_H

tests/chronotests.cpp

@@ -29,6 +29,7 @@ class ChronoTests : public TestFixture {
     CPPUNIT_TEST(testDateTime);
     CPPUNIT_TEST(testTimeSpan);
     CPPUNIT_TEST(testOperators);
+    CPPUNIT_TEST(testPeriod);
     CPPUNIT_TEST(testHashing);
     CPPUNIT_TEST_SUITE_END();
 
@@ -43,6 +44,7 @@ public:
     void testDateTime();
     void testTimeSpan();
     void testOperators();
+    void testPeriod();
     void testHashing();
 };
 
@@ -159,7 +161,26 @@ void ChronoTests::testOperators()
     dateTime += TimeSpan::fromDays(365);
     CPPUNIT_ASSERT_EQUAL(2000, dateTime.year());
     CPPUNIT_ASSERT_EQUAL(5, dateTime.day());
-    CPPUNIT_ASSERT_EQUAL(2, Period(dateTime, dateTime + TimeSpan::fromDays(62)).months());
+}
+
+/*!
+ * \brief Tests Period.
+ */
+void ChronoTests::testPeriod()
+{
+    const auto begin(DateTime::fromDateAndTime(1994, 7, 18, 15, 30, 21)), end(DateTime::fromDateAndTime(2017, 12, 2, 15, 30, 21));
+    const Period period(begin, end);
+    CPPUNIT_ASSERT_EQUAL(23, period.years());
+    CPPUNIT_ASSERT_EQUAL(4, period.months());
+    CPPUNIT_ASSERT_EQUAL(14, period.days());
+    CPPUNIT_ASSERT_EQUAL(end.toString(), (begin + period).toString());
+
+    const auto end2(DateTime::fromDateAndTime(2018, 1, 2, 15, 30, 21));
+    const Period period2(begin, end2);
+    CPPUNIT_ASSERT_EQUAL(23, period2.years());
+    CPPUNIT_ASSERT_EQUAL(5, period2.months());
+    CPPUNIT_ASSERT_EQUAL_MESSAGE("one more day, because December has 31 days", 15, period2.days());
+    CPPUNIT_ASSERT_EQUAL(end2.toString(), (begin + period2).toString());
 }
 
 /*!