#!/bin/sh

# Helper script to start/lock the screen with an available screen locker.

# Copyright (C) 2015  Simon Ruderich
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

set -eu


usage() {
    printf 'usage: %s start <lock time (min)> <lock binary>\n' "$0"
    printf '       %s lock\n' "$0"
    exit 1
}

installed() {
    type "$1" >/dev/null 2>&1
}


if test $# -eq 0; then
    usage
fi

if test x"$1" = xstart; then
    if test $# -ne 3; then
        usage
    fi
    lock_time_minutes="$2"
    lock_binary="$3"

    # NOTE: We must redirect stdout of the spawned background processes to
    # /dev/null or a potential caller which uses our output will wait forever
    # on the inherited stdin (and we become a zombie)! Thanks to Beano on [1]
    # for the idea, read on 2015-08-23.
    #
    # [1]: https://stackoverflow.com/questions/3748432/insane-crond-behavior-keeps-making-defunct-bash-processes/3750028#3750028

    if installed xscreensaver; then
        printf 'xscreensaver.timeout: %d
                xscreensaver.lock: True
                xscreensaver.lockTimeout: 0
               ' "$lock_time_minutes" | xrdb -merge
        xscreensaver >/dev/null &
        echo xscreensaver
    elif installed xautolock; then
        if installed "$lock_binary"; then
            # Terminate a running xautolock because we might have to replace
            # its timeout and other settings with our values.
            pkill -u "$USER" xautolock || true

            xautolock -secure -time "$lock_time_minutes" \
                      -locker "$lock_binary" \
                      >/dev/null &
            echo xautolock
        else
            echo "Locker '$lock_binary' not installed. Auto lock won't work!"
            exit 1
        fi
    else
        echo "No locker found. Auto lock won't work!"
        exit 1
    fi

elif test x"$1" = xlock; then
    if test $# -ne 1; then
        usage
    fi

    if installed xscreensaver; then
        # Start xscreensaver if it's not already running. xscreensaver-command
        # ensures xscreensaver is available for the current X session.
        xscreensaver-command -time >/dev/null 2>&1 || xscreensaver &

        # It can take a while for xscreensaver to start, wait until it's
        # ready. a || b && c behaves like (a || b) && c.
        while :; do
            xscreensaver-command -lock || test $? -ne 255 && break
        done
    elif installed xtrlock; then
        # Sleep is necessary to allow xtrlock to grab the keyboard input.
        sleep 1
        exec xtrlock
    elif installed xlock; then
        exec xlock
    elif installed i3lock; then
        exec i3lock
    else
        echo 'No screen locker found!'
        exit 1
    fi

else
    usage
fi