#!/bin/sh
set -eu

usage() {
	cat <<-'EOF'
		Usage:
		  highlight -n LINE_NUMBER -e PATTERN -f FILENAME
		  highlight -h
	EOF
}

help() {
	cat <<-'EOF'


		Options:
		  -n LINE_NUMBER    the specific line number to highligh
		  -e PATTERN        the pattern to highlight all over the file
		  -f FILENAME       the file to be processed
		  -h, --help        show this message


		Highlight FILENAME:
		  a) with an ANSI background color on LINE_NUMBER;
		  b) with an ANSI foreground color on every occurrence of PATTERN.

		Useful as a tool for development workflow, when one wants to
		show a specific matched line, and at the same time visualize all
		other ocurrences of PATTERN.


		Examples:

		  Highlight the line 10 of Makefile, and all occurences of "lisp":

		    $ highlight -n10 -e 'lisp' -f Makefile
	EOF
}


for flag in "$@"; do
	case "$flag" in
		(--)
			break
			;;
		(--help)
			usage
			help
			exit
			;;
		(*)
			;;
	esac
done

while getopts 'n:e:f:h' flag; do
	case "$flag" in
		(n)
			LINE_NUMBER="$OPTARG"
			;;
		(e)
			PATTERN="$OPTARG"
			;;
		(f)
			FILENAME="$OPTARG"
			;;
		(h)
			usage
			help
			exit
			;;
		(*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))

eval "$(assert-arg -- "${LINE_NUMBER:-}" '-n LINE_NUMBER')"
eval "$(assert-arg -- "${PATTERN:-}"     '-e PATTERN')"
eval "$(assert-arg -- "${FILENAME:-}"    '-f FILENAME')"



graybg="$(printf '\033[7;2;40m')"
end="$(printf '\033[0m')"

grep -E --color=always -e ^ -e "$PATTERN" "$FILENAME" |
	perl -pe "s/\x1b\[m/${end}${graybg}/g if $. == $LINE_NUMBER" |
	sed "${LINE_NUMBER}s|^\(.*\)\$|${graybg}\\1${end}|"
