#!/bin/sh

_printhelp()
{
    cat <<EOF
Usage: ${1##*/} [-m|-e] [-q] FILE

Display packages listed in FILE 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)
            _printhelp "$0"
            exit 1 ;;
        m)
            OPTION_FOREIGN="m" ;;
        q)
            OPTION_LOCAL="-2" ;;
        ?)
            _printhelp "$0"
            exit 1 ;;
    esac
done

shift $(($OPTIND - 1))

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

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

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

## Zsh version.
# comm -3 ${OPTION_LOCAL} <(pacman -Qq${OPTION_FOREIGN}${OPTION_EXPLICIT} | sort) <(sort "$*")