Add GncDateTime constructor taking a GncDate as parameter

As a GncDate doesn't have any time information, this has to be made up.
GnuCash uses 3 times-of-day quite a lot:
- start-of-day (00:00 local time)
- end-of-day (23:59 local time)
- neutral time (10:59 utc, chosen to minimize
  day offsetting when converting to/from localtime)

A second parameter to the new constructor will tell it to use one of these presets.

src/libqof/qof/gnc-datetime.cpp

@@ -100,6 +100,7 @@ public:
     GncDateTimeImpl() : m_time(boost::local_time::local_sec_clock::local_time(tzp.get(boost::gregorian::day_clock::local_day().year()))) {}
     GncDateTimeImpl(const time64 time) : m_time(LDT_from_unix_local(time)) {}
     GncDateTimeImpl(const struct tm tm) : m_time(LDT_from_struct_tm(tm)) {}
+    GncDateTimeImpl(const GncDateImpl& date, DayPart part = DayPart::neutral);
     GncDateTimeImpl(const std::string str);
     GncDateTimeImpl(PTime&& pt) : m_time(pt, tzp.get(pt.date().year())) {}
     GncDateTimeImpl(LDT&& ldt) : m_time(ldt) {}
@@ -132,10 +133,46 @@ public:
     std::string format_zulu(const char* format) const;
 private:
     Date m_greg;
+
+    friend GncDateTimeImpl::GncDateTimeImpl(const GncDateImpl&, DayPart);
 };
 
 /* Member function definitions for GncDateTimeImpl.
  */
+GncDateTimeImpl::GncDateTimeImpl(const GncDateImpl& date, DayPart part) :
+    m_time(unix_epoch, utc_zone)
+{
+    using TD = boost::posix_time::time_duration;
+    static const TD start(0, 0, 0);
+    static const TD neutral(10, 59, 0);
+    static const TD end(23,59, 0);
+    TD time_of_day;
+    switch (part)
+    {
+        case DayPart::start:
+            time_of_day = start;
+            break;
+        case DayPart::neutral:
+            time_of_day = neutral;
+            break;
+        case DayPart::end:
+            time_of_day = end;
+            break;
+    }
+
+    try
+    {
+        auto tz = utc_zone;
+        if (part != DayPart::neutral)
+            tz = tzp.get(date.m_greg.year());
+        m_time = LDT(date.m_greg, time_of_day, tz, LDT::EXCEPTION_ON_ERROR);
+    }
+    catch(boost::gregorian::bad_year)
+    {
+        throw(std::invalid_argument("Time value is outside the supported year range."));
+    }
+}
+
 GncDateTimeImpl::GncDateTimeImpl(const std::string str) :
     m_time(unix_epoch, utc_zone)
 {
@@ -286,6 +323,9 @@ GncDateTime::GncDateTime(const std::string str) :
     m_impl(new GncDateTimeImpl(str)) {}
 GncDateTime::~GncDateTime() = default;
 
+GncDateTime::GncDateTime(const GncDate& date, DayPart part) :
+    m_impl(new GncDateTimeImpl(*(date.m_impl), part)) {}
+
 void
 GncDateTime::now()
 {

src/libqof/qof/gnc-datetime.hpp

@@ -36,6 +36,12 @@ typedef struct
     int day; //1-31
 } ymd;
 
+enum class DayPart {
+    start,  // 00:00
+    neutral,  // 10:59
+    end,  // 23:59
+};
+
 class GncDateTimeImpl;
 class GncDateImpl;
 class GncDate;
@@ -77,6 +83,21 @@ public:
  * @exception std::invalid_argument if the year is outside the constraints.
  */
     GncDateTime(const struct tm tm);
+/** Construct a GncDateTime from a GncDate. As a GncDate doesn't contain time
+ * information, the time will be set depending on the second parameter
+ * to start of day, neutral or end of day.
+ * @param date: A GncDate representing a date.
+ * @param part: An optinoal DayPart indicating which time to use in the conversion.
+ * This can be "DayPart::start" for start of day (00:00 local time),
+ *             "DayPart::neutral" for a neutral time (10:59 UTC, chosen to have the
+ *              least chance of date changes when crossing timezone borders),
+ *             "DayPart::end" for end of day (23:59 local time).
+ * If omitted part defaults to DayPart::neutral.
+ * Note the different timezone used for DayPart::neutral compared to the other
+ * two options!
+ * @exception std::invalid_argument if the year is outside the constraints.
+ */
+    GncDateTime(const GncDate& date, DayPart part = DayPart::neutral);
 /** Construct a GncDateTime
  * @param str: A string representing the date and time in some
  * recognizable format. Note that if a timezone is not specified the
@@ -174,6 +195,8 @@ class GncDate
 
 private:
     std::unique_ptr<GncDateImpl> m_impl;
+
+    friend GncDateTime::GncDateTime(const GncDate&, DayPart);
 };
 
 #endif // __GNC_DATETIME_HPP__

src/libqof/qof/test/gtest-gnc-datetime.cpp

@@ -71,6 +71,35 @@ TEST(gnc_datetime_constructors, test_struct_tm_constructor)
     EXPECT_EQ(tm1.tm_min, tm.tm_min);
 }
 
+/* Note: the following tests for the constructor taking a GncDate as input parameter
+ * use GncDateTime's format() member function to simplify the result checking.
+ * If there's a bug in this member function, these tests may fail in addition
+ * to the format test later in the test suite. Be sure to check that later
+ * test as well in case any of the below constructor tests fails. */
+
+TEST(gnc_datetime_constructors, test_gncdate_start_constructor)
+{
+    const ymd aymd = { 2017, 04, 20 };
+    GncDateTime atime(GncDate(aymd.year, aymd.month, aymd.day), DayPart::start);
+    //Skipping timezone information as this can't be controlled.
+    EXPECT_EQ(atime.format("%d-%m-%Y %H:%M:%S"), "20-04-2017 00:00:00");
+}
+
+TEST(gnc_datetime_constructors, test_gncdate_end_constructor)
+{
+    const ymd aymd = { 2046, 11, 06 };
+    GncDateTime atime(GncDate(aymd.year, aymd.month, aymd.day), DayPart::end);
+    //Skipping timezone information as this can't be controlled.
+    EXPECT_EQ(atime.format("%d-%m-%Y %H:%M:%S"), "06-11-2046 23:59:00");
+}
+
+TEST(gnc_datetime_constructors, test_gncdate_neutral_constructor)
+{
+    const ymd aymd = { 2017, 04, 20 };
+    GncDateTime atime(GncDate(aymd.year, aymd.month, aymd.day), DayPart::neutral);
+    EXPECT_EQ(atime.format("%d-%m-%Y %H:%M:%S %z"), "20-04-2017 10:59:00 UTC");
+}
+
 TEST(gnc_datetime_functions, test_format)
 {
     GncDateTime atime(2394187200); //2045-11-13 12:00:00 Z