#!/bin/sh

usage () {
	cat <<EOF>&2
Usage: ${0##*/} [-m] [-e] [-q] FILES...

Display packages listed in FILES but not installed.

  -e:  Compare FILE to explicitly installed packages.
  -h:  Display this help.
  -m:  Compare FILE to foreign installed packages.
  -q:  Display installed packages not included in FILE.
EOF
}

OPTION_EXPLICIT=""
OPTION_FOREIGN=""
OPTION_LOCAL="-1"

while getopts ":hmqe" opt; do
	case $opt in
	e)
		OPTION_EXPLICIT="e" ;;
	h)
		usage
		exit 1 ;;
	m)
		OPTION_FOREIGN="m" ;;
	q)
		OPTION_LOCAL="-2" ;;
	\?)
		usage
		exit 1 ;;
	esac
done

shift $((OPTIND - 1))

if [ $# -eq 0 ]; then
	echo "Missing argument."
	usage
	exit 1
fi

if ! command -v pacman >/dev/null 2>&1; then
	echo >&2 "'pacman' not found"
	exit 1
fi

PKGLIST="$(mktemp)"
FILE="$(mktemp)"
pacman -Qq${OPTION_FOREIGN}${OPTION_EXPLICIT} | LC_ALL=C sort > "$PKGLIST"
LC_ALL=C sort "$@" > "$FILE"
LC_ALL=C comm -3 ${OPTION_LOCAL} "$PKGLIST" "$FILE"
rm -f "$PKGLIST" "$FILE"