From 73f75393e9f451add7a8bc02739119966c5c4cea Mon Sep 17 00:00:00 2001
From: Martchus <martchus@gmx.net>
Date: Sun, 3 Dec 2017 14:46:10 +0100
Subject: [PATCH] WIP

---
 chrono/datetime.h     | 51 +++++++++++++++++++++++++++++++++++++++++++
 chrono/timespan.h     |  2 ++
 tests/chronotests.cpp |  4 ++++
 3 files changed, 57 insertions(+)

diff --git a/chrono/datetime.h b/chrono/datetime.h
index e461df7..4231843 100644
--- a/chrono/datetime.h
+++ b/chrono/datetime.h
@@ -49,6 +49,8 @@ enum class DatePart {
     Day /**< day */
 };
 
+struct Date;
+
 class CPP_UTILITIES_EXPORT DateTime {
 public:
     explicit constexpr DateTime();
@@ -70,6 +72,7 @@ public:
     int day() const;
     int dayOfYear() const;
     constexpr DayOfWeek dayOfWeek() const;
+    constexpr Date date() const;
     constexpr int hour() const;
     constexpr int minute() const;
     constexpr int second() const;
@@ -505,6 +508,54 @@ inline DateTime &DateTime::operator-=(const TimeSpan &timeSpan)
     m_ticks -= timeSpan.m_ticks;
     return *this;
 }
+
+struct Date {
+    constexpr Date(DateTime dateTime);
+
+    int year;
+    int month;
+    int day;
+};
+
+constexpr Date::Date(DateTime dateTime)
+    : year(0)
+    , month(0)
+    , day(0)
+{
+    const int fullDays = dateTime.totalTicks() / TimeSpan::m_ticksPerDay;
+    const int full400YearBlocks = fullDays / DateTime::m_daysPer400Years;
+    const int daysMinusFull400YearBlocks = fullDays - full400YearBlocks * m_daysPer400Years;
+    int full100YearBlocks = daysMinusFull400YearBlocks / m_daysPer100Years;
+    if (full100YearBlocks == 4) {
+        full100YearBlocks = 3;
+    }
+    const int daysMinusFull100YearBlocks = daysMinusFull400YearBlocks - full100YearBlocks * m_daysPer100Years;
+    const int full4YearBlocks = daysMinusFull100YearBlocks / m_daysPer4Years;
+    const int daysMinusFull4YearBlocks = daysMinusFull100YearBlocks - full4YearBlocks * m_daysPer4Years;
+    int full1YearBlocks = daysMinusFull4YearBlocks / m_daysPerYear;
+    if (full1YearBlocks == 4) {
+        full1YearBlocks = 3;
+    }
+    if (part == DatePart::Year) {
+        return full400YearBlocks * 400 + full100YearBlocks * 100 + full4YearBlocks * 4 + full1YearBlocks + 1;
+    }
+    const int restDays = daysMinusFull4YearBlocks - full1YearBlocks * m_daysPerYear;
+    if (part == DatePart::DayOfYear) { // day
+        return restDays + 1;
+    }
+    const int *const daysToMonth = (full1YearBlocks == 3 && (full4YearBlocks != 24 || full100YearBlocks == 3)) ? m_daysToMonth366 : m_daysToMonth365;
+    int month = 1;
+    while (restDays >= daysToMonth[month]) {
+        ++month;
+    }
+    if (part == DatePart::Month) {
+        return month;
+    } else if (part == DatePart::Day) {
+        return restDays - daysToMonth[month - 1] + 1;
+    }
+    return 0;
+}
+
 } // namespace ChronoUtilities
 
 namespace std {
diff --git a/chrono/timespan.h b/chrono/timespan.h
index 04a2fc4..0b5235e 100644
--- a/chrono/timespan.h
+++ b/chrono/timespan.h
@@ -14,6 +14,7 @@
 namespace ChronoUtilities {
 
 class DateTime;
+struct Date;
 
 /*!
  * \brief Specifies the output format.
@@ -27,6 +28,7 @@ enum class TimeSpanOutputFormat {
 
 class CPP_UTILITIES_EXPORT TimeSpan {
     friend class DateTime;
+    friend struct Date;
 
 public:
     explicit constexpr TimeSpan();
diff --git a/tests/chronotests.cpp b/tests/chronotests.cpp
index cb07ddc..3f6f39d 100644
--- a/tests/chronotests.cpp
+++ b/tests/chronotests.cpp
@@ -105,6 +105,10 @@ void ChronoTests::testDateTime()
     const auto delta = DateTime::gmtNow() - DateTime::exactGmtNow();
     CPPUNIT_ASSERT(delta < TimeSpan::fromSeconds(2) && delta > TimeSpan::fromSeconds(-2));
 #endif
+
+    // test boundaries
+    CPPUNIT_ASSERT_EQUAL("0001-01-01 00:00:00"s, DateTime().toString());
+    CPPUNIT_ASSERT_EQUAL("58456-05-28 05:36:10.955"s, DateTime::eternity().toString());
 }
 
 /*!