#!/usr/bin/env perl

use strict;
use warnings;
use 5.010;

use JSON qw( decode_json );     # isn't default module, must be installed via CPAN or your system package manager
use Time::HiRes qw ( usleep );  # for simple delays

my $outputfile = shift;                       # getting output filename from command-line params
my $command    = 'i3-msg -t get_workspaces';  # console command used to get the list of active workspaces
my $fileprefix = '/tmp/i3shot-';              # prefix for temporary screenshots

my $json = `$command`;
my $decoded = decode_json($json);

foreach my $workspace (@{$decoded}) {
    # get the name of current workspace
    my $current = $workspace->{'name'};
    # move there
    `i3-msg workspace $current`;
    # a short delay — some windows couldn't be drawn in a moment, and we get a rubbish
    usleep(200000);
    # and take screenshot of all the display and save it to temporary file
    `import -window root ${fileprefix}${current}.png`;
}

# montage — an utility from ImageMagick to combine multiple images to a single one
# parameters' values: -geometry — we don't need neither resizes nor shifts; -tile — put all images in a single row
`montage ${fileprefix}*.png -geometry +0+0 -tile x1 ${outputfile}`;