#!/usr/bin/perl

# Written by Mason Loring Bliss.
# This program is explicitly in the public domain.

use strict;
use warnings;

my $wmctrl = '/usr/bin/wmctrl';
my $xprop = '/usr/bin/xprop';

my $aw;
my $ad;
my @potentials;
my %overlaps;
my %w;

my $command = shift || 'nothing';
if ($command ne "left" && $command ne "right"
    && $command ne "up" && $command ne "down") {
    print "Sorry, need one of 'left', 'right', 'up', or 'down'.\n";
    exit 1;
}

if (! -f $xprop) {
    print "Sorry, we need $xprop to continue.\n";
    exit 1;
}

if (! -f $wmctrl) {
    print "Sorry, we need $wmctrl to continue.\n";
    exit 1;
}

# Find active window.
open my $query, "$xprop -root|";
while (<$query>) {
    last if /_NET_ACTIVE_WINDOW/;
}
(undef, undef, undef, undef, $aw) = split;
close $query;
$aw = sprintf("0x%08x", hex($aw));

# Gather list of desktops, and note active desktop.
open $query, "$wmctrl -d|";
while (<$query>) {
    my ($dnum, $starred, undef) = split;
    if ($starred eq '*') {
        $ad = $dnum;
        last;
    }
}
close $query;

# Gather list of windows on the active desktop, and their geometry.
open $query, "$wmctrl -l -G|";
while (<$query>) {
    my ($win, $desktop, $x, $y, $w, $h, undef) = split;
    next if $desktop ne $ad;
    # XXX possibly consider excluding gnome-panel

    $w{$win}{x} = $x;
    $w{$win}{y} = $y;
    $w{$win}{w} = $w;
    $w{$win}{h} = $h;
}
close $query;

# Identify windows to consider.
if ($command eq 'left') {
    @potentials = grep {$w{$_}{x} < $w{$aw}{x}} keys %w;
} elsif ($command eq 'right') {
    @potentials =
            grep {$w{$_}{x} + $w{$_}{w} > $w{$aw}{x} + $w{$aw}{w}} keys %w;
} elsif ($command eq 'up') {
    @potentials = grep {$w{$_}{y} < $w{$aw}{y}} keys %w;
} else { # $command eq 'down'
    @potentials =
            grep {$w{$_}{y} + $w{$_}{h} > $w{$aw}{y} + $w{$aw}{h}} keys %w;
}
for (@potentials) {
    # Find x overlap.
    if ($w{$_}{x} < $w{$aw}{x}
            && $w{$_}{x} + $w{$_}{w} > $w{$aw}{x} + $w{$aw}{w}) {
        $overlaps{$_}{x} = $w{$aw}{w};
    } elsif ($w{$_}{x} > $w{$aw}{x}
            && $w{$_}{x} + $w{$_}{w} < $w{$aw}{x} + $w{$aw}{w}) {
        $overlaps{$_}{x} = $w{$aw}{w};
    } elsif ($w{$_}{x} < $w{$aw}{x}) {
        $overlaps{$_}{x} = $w{$_}{x} + $w{$_}{w} - $w{$aw}{x};
    } else {
        $overlaps{$_}{x} = $w{$aw}{x} + $w{$aw}{w} - $w{$_}{x};
    }

    # Find y overlap.
    if ($w{$_}{y} < $w{$aw}{y}
            && $w{$_}{y} + $w{$_}{h} > $w{$aw}{y} + $w{$aw}{h}) {
        $overlaps{$_}{y} = $w{$aw}{h};
    } elsif ($w{$_}{y} > $w{$aw}{y}
            && $w{$_}{y} + $w{$_}{h} < $w{$aw}{y} + $w{$aw}{h}) {
        $overlaps{$_}{y} = $w{$aw}{h};
    } elsif ($w{$_}{y} < $w{$aw}{y}) {
        $overlaps{$_}{y} = $w{$_}{y} + $w{$_}{h} - $w{$aw}{y};
    } else {
        $overlaps{$_}{y} = $w{$aw}{y} + $w{$aw}{h} - $w{$_}{y};
    }

    if ($command eq 'left' || $command eq 'right') {
        $overlaps{$_}{value} = $overlaps{$_}{y} * 1.5 + $overlaps{$_}{x};
    } else {
        $overlaps{$_}{value} = $overlaps{$_}{y} + $overlaps{$_}{x} * 1.5;
    }
}

# If there are no potentials, don't move. Otherwise, find the largest value.
if (@potentials) {
    my $winner;
    my $high_water_mark;
    for (@potentials) {
        $winner //= $_;
        $high_water_mark //= $overlaps{$_}{value};
        if ($overlaps{$_}{value} > $high_water_mark) {
            $winner = $_;
            $high_water_mark = $overlaps{$_}{value};
        }
    }
    system("$wmctrl -i -a $winner");
}