#Display calendar with arrow key navigation for month and year.

#!/bin/bash
#Display calendar with arrow key navigation for month and year.
# By The Free Thinker, 2020. gopher://aussies.space/1/~freet/
#
#Usage:
# browsecal.sh [cal args] [-m month] [-y year]
#
#See "man cal" for "cal args".
#
# UP = next year, DOWN = last year, RIGHT = next month,
# LEFT = last month, SPACE = current month/year, q = quit.
#
#Example usage:
# browsecal.sh -3 -y 2013 -m 1
# urxvt -geometry 22x9 -title "Calendar" -e browsecal.sh

clear

#Process command-line arguments:
calargs=
until [ -z "$1" ]
do
case "$1" in
"-m") shift; [ ! -z "${1##*[!0-9]*}" ] && month=$1 || month=`date -d "$1 1" +%-m` ;; #https://stackoverflow.com/a/2704760
"-y") shift; year=$1 ;;
*) calargs="$calargs $1" ;;
esac
shift
done

[ -z $month ] && month=`date +%-m`
[ -z $year ] && year=`date +%-Y`

cal $calargs $month $year || exit

oldIFS="$IFS"
IFS=
#Arrow key reading from:
# https://stackoverflow.com/a/46481173
escape_char=$(printf "\u1b")
while true
do
read -rsn1 mode # get 1 character
if [[ $mode == $escape_char ]]; then
read -rsn2 mode # read 2 more chars
fi
case $mode in
#key q
'q') exit ;;

#key SPACE
' ') IFS=" "
month=`date +%-m`
year=`date +%-Y`
clear
cal $calargs $month $year
IFS=
;;

#key UP
'[A') IFS=" "
(( year++ ))
clear
cal $calargs $month $year
IFS=
;;

#key DOWN
'[B') IFS=" "
[ $year -gt 1 ] && (( year-- ))
clear
cal $calargs $month $year
IFS=
;;

#key LEFT
'[D') IFS=" "
if [ $month -gt 1 ]; then
(( month-- ))
else
(( year-- ))
month=12
fi
clear
cal $calargs $month $year
IFS=
;;

#key RIGHT
'[C') IFS=" "
if [ $month -lt 12 ]; then
(( month++ ))
else
(( year++ ))
month=1
fi
clear; cal $calargs $month $year
IFS=
;;
esac
done

IFS="$oldIFS"