autoredshift

#!/usr/bin/env sh

seconds() {
	# the `while` is only used to capture the variables. It's not expect to loop
	echo $@ | while IFS=: read -r hours minutes seconds;
	do echo "${hours:-0} * 3600 + ${minutes:-0} * 60 + ${seconds:-0}" |
	bc #using bc instead of shell arithmetic to avoid the funny octal bug
	done
}


fadein_start=$(seconds 19:00)
fadein_end=$(seconds 23:00)
fadeout_start=$(seconds 4:00)
fadeout_end=$(seconds 5:00)

max_temp=6500
min_temp=1000

interpolated_temp() {
	local min=$1
	local max=$2
	local val=$3

	echo $((min_temp + (max_temp - min_temp) * (val - min) / (max - min)))
}

set_time=$(seconds ${1:-$(date +%H:%M)})
#NOTE: this assumes fadeout happens earlier in the day than fadein
if test $set_time -lt $fadeout_start;
	then TEMP=$min_temp
elif test $set_time -lt $fadeout_end;
	then TEMP=$(interpolated_temp $fadeout_start $fadeout_end $set_time)
elif test $set_time -lt $fadein_start;
	then TEMP=$max_temp
elif test $set_time -lt $fadein_end;
	then TEMP=$(interpolated_temp $fadein_end $fadein_start $set_time)
else
	TEMP=$min_temp
fi

redshift -PO "$TEMP" >/dev/null
echo $TEMP