calc_sun reported sun trajectory in seconds since the start of a UTC
day, as they would occur for the specified UTC day. The caller would
then add the UTC timestamp for the start of a UTC day to these numbers.
This lead to complications, as e.g. a sunrise in China would be a
negative value, as it occurred in the last UTC day.
Futhermore, the start of a UTC day was used to signal the need for new
sun calculations. This would lead to recalculations to possibly occur
after its results were needed, such as after sunrise when the target
longitude deviated significantly from the prime meridian.
To fix this, we apply longitude time correction to the start of day
calculation. This way recalculation will occur on the start of the
longitude local day, close midnight for the observer.
We also remove the longitude time correction from calc_sun, so that it
simply returning the number of seconds since the start of the local day
of the observer. The caller then adds the start of the longitude local
day to get the final numbers.
The sun trajectory calculation previously emitted garbage if midnight
sun or polar night phenomena was in effect. To fix this, the calculation
is overhauled to report if the computation failed, and if so, which
specific phenomena was the cause.
Timing recalulation uses this information to change out of the normal
state that uses the four sun position timings, into a static state where
wlsunset simply waits a day at a time for a normal sun trajectory
pattern to be restored. In this state, a fixedc high/low temperature is
set as appropriate for the phenomena.
A transition phase replicating the previous day's sunrise is used to
smooth out entry into a midnight sun, which would otherwise cause a
jarring instant-daylight setting.
Kenny Levinsen