#! /usr/bin/perl

=for comment
This is a script to add rotational behavior to the disper nvidia 
display changing utility.

Repeated invocations of this script will do this:
   laptop display only -> external only
   external only -> both displays
   both displays -> laptop display only
   etc..
=cut

use strict;
use warnings;


# Args that are always needed for disper

my $disperArgs = '--scaling native ';


# Use nvidia-settings to get the AssociatedDisplays and TwinView status

my $nvsetQueryOutput = `nvidia-settings --query=AssociatedDisplays --query=TwinView`;

my ($nvsetTwinView) = $nvsetQueryOutput =~
      /Attribute 'TwinView' \(.*\): (\d)\./;

my ($nvsetAssociatedDisplays) = $nvsetQueryOutput =~
      /Attribute 'AssociatedDisplays' \(.*\): 0x\d{7}(\d)\./;


# Configure args for disper

SWITCH: {
   # Laptop display only now, switch to external only
   if ($nvsetTwinView == 0 && $nvsetAssociatedDisplays == 0)
      { $disperArgs .= '--secondary'; last SWITCH; }

   # External monitor only now, switch to both
   if ($nvsetTwinView == 0 && $nvsetAssociatedDisplays == 1)
      { $disperArgs .= '--extend'; last SWITCH; }

   # Both monitors now, switch to laptop only
   if ($nvsetTwinView == 1 && $nvsetAssociatedDisplays == 1)
      { $disperArgs .= '--single'; last SWITCH; }
}


# Perform the switch

system "disper $disperArgs";


# Extra fun stuff

# Screen metrics have possibly (probably?) changed, root window 
# background probably borken now.

# Reinstate my beloved root window image. I use feh for this, so:
my $rootImgSetter = "$ENV{HOME}/.fehbg";
system "eval `cat $rootImgSetter`" if -e $rootImgSetter;