GroupStageWithEqualQualityGroups.php

<?php

/**
 * Pool 1: Rank 1, 8, 9, 16, 17
 * Pool 2: Rank 2, 7, 10, 15
 * Pool 3: Rank 3, 6, 11, 14
 * Pool 4: Rank 4, 5, 12, 13
 */
function seed_partition(array $teams, $groups = 1)
{
    $teamCount = count($teams);

    $seeds = range(1, $teamCount);
    $seeds = array_chunk($seeds, $groups);

    $g = 1;
    $orderedList = [];
    foreach ($seeds as $chunk) {
        if ($g % 2 === 0) {
            $chunk = array_reverse($chunk);
        }

        foreach ($chunk as $item => $value) {
            $orderedList[] = $value;
        }

        $g++;
    }

    $divisions = [];
    $r = 1;
    foreach ($orderedList as $seed) {
        $divisions[$r][] = $seed;

        if ($r % $groups !== 0) {
            $r++;
        } else {
            $r = 1;
        }
    }

    return $divisions;
}