#!/usr/bin/perl

# Yevgen Matusevych, 10.12.2018.
# Tested on Scientific Linux 7.5, GNOME version 3.22.2.

# This script monitors locking and unlocking events of xscreensaver.
# Upon locking, the layout map is set to US-only.
# Upon unlocking, the original system layout map (recorded at the script runtime) is recovered.

# In case of problems upon unlocking, run the following shell command:
# setxkbmap -layout $PREFERRED_LAYOUT_MAP
# e.g.:
# setxkbmap -layout gb,ru,us

# Resources:
# https://www.x.org/archive/X11R7.7/doc/man/man1/setxkbmap.1.xhtml
# https://wiki.gentoo.org/wiki/Keyboard_layout_switching

my $system_layout = `setxkbmap -query | grep layout | cut -f6 -d' '`;

my $blanked = 0;
open (IN, "xscreensaver-command -watch |");
while (<IN>) {
    if (m/^(BLANK|LOCK)/) {
        if (!$blanked) {
            system("setxkbmap -layout us");
            $blanked = 1;
        }
    } elsif (m/^UNBLANK/) {
        system("setxkbmap -layout $system_layout");
        $blanked = 0;
    }
}