#!/usr/bin/perl
use strict;
use warnings;

my $match45 = isCorrectPath (0, 0, 10, 10);

for my $pair ([0, 0], [-1, 0], [-4, 0], [5, 5], [1, 5]) {
    if ($match45->(@$pair)) {
        print "Match 45 for @$pair\n";
    } else {
        print "Fail 45 for @$pair\n";
    }
}

my $match0 = isCorrectPath (0, 0, 10, 0);

for my $pair ([0, 0], [0, -1], [0, -4], [5, 5], [100, 2]) {
    if ($match0->(@$pair)) {
        print "Match 0 for @$pair\n";
    } else {
        print "Fail 0 for @$pair\n";
    }
}

my $match90 = isCorrectPath (0, 0, 0, 10);

for my $pair ([0, 0], [-1, -0], [-4, 0], [5, 5], [2, 100]) {
    if ($match90->(@$pair)) {
        print "Match 90 for @$pair\n";
    } else {
        print "Fail 90 for @$pair\n";
    }
}


sub isCorrectPath {
    my ($x1, $y1, $x2, $y2) = @_;
    my $difx = ($x2 - $x1);
    my $slope = $difx ? ($y2 - $y1) / $difx : undef;

    return sub {
        my ($x, $y) = @_;
        my $xmin = ($x - $x1);

        return abs($x - $x1) < 3    # Vertical line: allow 3 units either side
            if !defined $slope;

        return abs($y - $y1) < 3    # Horizontal line: allow 3 units either side
            if !$slope;

        return abs(($slope * ($x - $x1)) - ($y - $y1)) < 3;
    };
}

##</code><code>##

Match 45 for 0 0
Match 45 for -1 0
Fail 45 for -4 0
Match 45 for 5 5
Fail 45 for 1 5
Match 0 for 0 0
Match 0 for 0 -1
Fail 0 for 0 -4
Fail 0 for 5 5
Match 0 for 100 2
Match 90 for 0 0
Match 90 for -1 0
Fail 90 for -4 0
Fail 90 for 5 5
Match 90 for 2 100