gensuntimes

#!/usr/bin/env bash
###########################################################################
# Made by    : E. Dronkert
# Licence    : GNU GPL v3
# Platform   : MacOS, Raspbian
# Requires   : bash, sun, date, uname
# Location   : ~/bin/
# Name       : gensuntimes
# Version    : 1.0.0
# Date       : 2024-03-13
# Purpose    : Calculate local sunrise, sunset times & daylight duration
#              for a whole year for several places, save in text files.
# Parameters : Optional year (default = this year, or next year in Dec.)
# Settings   : Places on line 63.
# Output     : Text files 'sun_<place>_<year>.txt' with output of 'sun' for
#              every day of the year.
# Exit     0 : No errors
#          1 : Companion script 'sun' not found
#          2 : OS is not MacOS or Linux
###########################################################################

app=$(which sun)
if [ ! -x "$app" ]; then
	echo "Program 'sun' not found." >&2
	exit 1
fi

# Darwin (macOS) or Linux (Raspbian)
OS=$(uname)
if [ "$OS" != "Darwin" -a "$OS" != "Linux" ]; then
	echo "Unknown operating system: $OS" >&2
	exit 2
fi

# Is the first argument a year?
y=
if [ -n "$1" ]; then
	if [ ${#1} -eq 4 ]; then
		if (( $1 >= 1900 && $1 < 2200 )); then
			y=$1
		fi
	fi
fi

# No argument or invalid year?
if [ -z "$y" ]; then
	# Use current year, next year if December
	y=$(date +%Y)
	m=$(date +%m)
	[ "$m" -eq "12" ] && (( ++y ))
fi

echo "Calculate sunrise and sunset times for the year $y:"

# Number of days in the year, either 365 or 366
if [ "$OS" = "Darwin" ]; then
	n=$(date -j 12310000$y +%j)
else
	n=$(date -d $y-12-31 +%j)
fi

# For different places
for p in utrecht ouddorp baarn amstelveen; do

	printf '%-15s' "$p"
	f="sun_${p}_${y}.txt"

	# Test if empty file can be created
	if [ -e "$f" ]; then
		if [ ! -f "$f" ]; then
			echo "Exists but not a file: $f" >&2
			continue
		fi
		if [ ! -w "$f" ]; then
			echo "Can't overwrite: $f" >&2
			continue
		fi
	fi

	# Start with empty file with the right permissions
	: 2> /dev/null 1> "$f"
	chmod -f 600 "$f" &> /dev/null

	# Is it safe?
	if [ ! -f "$f" -o ! -w "$f" ]; then
		echo "Could not create: $f" >&2
		continue
	fi

	# For every day in the year
	for (( i = 0; i < n; ++i )); do

		# Date in yyyy-mm-dd format
		if [ "$OS" = "Darwin" ]; then
			d=$(date -j -v +${i}d 01010000$y.00 +%Y-%m-%d)
		else
			d=$(date -d "$y-01-01 +$i day" -I)
		fi

		# Progress report
		[ "${d: -2}" = "01" ] && echo -n '.'

		# sunrise/sunset/daylight times, comma separated
		t=$(sun -csv $p $d)

		# Add to file
		echo "$d,$t" >> "$f"

	done
	echo " $f"
done