#!/bin/sh
set -eu

usage() {
	cat <<-'EOF'
		Usage:
		  e [FILE]
		  e -h
	EOF
}

help() {
	cat <<-'EOF'

		Options:
		  -h, --help


		Flexibly run a text editor, either directly on in a pipe.

		Examples:

		  Edit "file.txt":

		    $ e file.txt

		  Manipulate the content of a pipe midway:

		    $ seq 10 | e | grep 5

		The editor used is either $VISUAL or $EDITOR, with a fallback to
		vi in case any of those variables aren't defined.
	EOF
}

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

while getopts 'h' flag; do
	case "$flag" in
		h)
			usage
			help
			exit
			;;
		*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))


CMD="${VISUAL:-${EDITOR:-vi}}"

if [ ! -t 0 ]; then
	F="$(mkstemp)"
	cat > "$F"
	exec 0</dev/tty
	exec 3>&1
	exec 1>/dev/tty
	$CMD "$F"
	cat "$F" >&3
else
	$CMD "$@"
fi