# When and where will it become daylight / night time on your next
# flight? Well, just download the previous day's flight's .kml track
# log and compute!
#
# Usage example: Making a .solar.txt out of a .kml present in the directory:
# make FlightAware_UAL872_RCTP_KSFO_20220706.solar.csv
#
# This Makefile you are reading will compute the mean solar time of
# points on a flight, and thus tell you where it will get dark (around
# 18:00), or light (around 06:00). Yes, seasons are disregarded, as so
# is even latitude. Sorry.
#
# Author: Dan Jacobson https://www.jidanni.org/
# Copyright: https://www.gnu.org/licenses/gpl.html
# Created: 2023-03-22T02:39:40+0000
# Last-Updated: 2023-03-27T05:37:46+0000
#     Update #: 118
# https://en.wikipedia.org/wiki/Solar_time#Mean_solar_time
S=sqlite3 -bail
# https://www.sqlite.org/lang_datefunc.html
%.solar.csv:%.sqlite; echo "SELECT Latitude, Longitude,  \
	strftime('%Y-%m-%dT%H:%M:%S', Time, (Longitude / 15 )||' hours') \
	AS 'Mean solar time' FROM t1;"|$S --csv --header $? > $@
%.sqlite:%.csv; echo .import --csv $? t1|$S $@
%.csv:%.kml %.style; TZ= gpsbabel -t -i kml -f $< -x nuketypes,waypoints -o xcsv,style=$*.style -F $@
# https://www.gpsbabel.org/htmldoc-development/style_define.html
%.style:; echo $(style)|perl -pwle 's/\s*\@/\n/g;' > $@
style=\
FIELD_DELIMITER COMMA\
@RECORD_DELIMITER NEWLINE\
@PROLOGUE Latitude,Longitude,Time\
@IFIELD LAT_DECIMAL,"","%f"\
@IFIELD LON_DECIMAL,"","%f"\
@IFIELD ISO_TIME,"","%s"
# Time shifting to mean solar time would be too much to ask
# https://www.gpsbabel.org/htmldoc-development/filter_track.html
# to implement for so few users, so we do it ourselves above!

# One notices at high latitudes, westbound planes can even "turn back
# the hands of time".