https://eval.in/74923

kris_kringle.php

<?php

$names = ['Fred', 'Wilma', 'Pebbles', 'Barney', 'Betty', 'Bamm-Bamm'];
$count = count($names);

$count % 2 === 0 || exit('Error! You need an even number of names.');

shuffle($names);

$a = array_slice($names, 0, $count / 2);
$b = array_slice($names, $count / 2, $count);

$match = function($givers, $receivers)
{
    shuffle($receivers);

    return array_map(function($giver, $receiver) {
        return sprintf('%s buys for %s', $giver, $receiver);
    }, $givers, $receivers);
};

echo implode(PHP_EOL, array_merge($match($a, $b), $match($b, $a)));