#!/bin/bash

message="Valid entries are: <num>-<num>, <num>-,-<num>, <num>, ''"
path=$( readlink -f $0 )
path=${path%/*}
printf '%s\n' "Chapters:"
for num in {0..19}; do
	file="$path/chapter$num.txt"
	(( ${#num} == 1 )) && num="0$num"
	h=$( grep -m1 . $file )
	h=${h:2}                       # rm first 2 chars ('# ')
#	h="${h#"${h%%[![:space:]]*}"}" # rm leading white spaces
	h=${h,,}                       # all to lowercase
	h=${h^}                        # first to uppercase
	printf '%s\n' "$num: $h"
done

re_num='^[0-9]+$'
while true; do
	read -p "Input range: " range
	# echo "you chose $range"
	start=${range%%-*}
	: ${start:=0}
	end=${range##*-}
	: ${end:=19}
	# echo "start is $start and end is $end"
	[[ $start =~ $re_num ]] && [[ $end =~ $re_num ]] && break || echo "Not a valid range. $message"
done

for num in {0..19}; do
	file="$path/chapter$num.txt"
	(( $num >= $start )) && (( $num <= $end )) && pandoc -s --from=markdown --to=pdf $file | zathura -
#	(( $num >= $start )) && (( $num <= $end )) && printf '%s\n' "$file"
done