Simple regexp router

router.php

<?php declare(strict_types=1);

$routes = [
    ['GET /(?<something_file>[a-z][a-z0-9]{8}\.[a-z0-9]{3,4})', '...meta...'],
    ['GET /(?<ok>what|na)', '...meta...'],
    ['POST /', '...meta...'],
];

$regexp = implode('|', array_map(   // could be cached
    static function (int $index, array $values) {
        return sprintf('^(?<_%s>%s)$', $index, str_replace('(?<', "(?<_{$index}_", $values[0]));
    },
    array_keys($routes),
    $routes,
));

$attrs = [];
$routesIndex = matchRoute($regexp, 'GET', '/what', $attrs);

function matchRoute(string $regexp, string $method, string $path, array &$attributes = []): ?int
{
    if (preg_match("#$regexp#i", "$method $path", $matches, PREG_UNMATCHED_AS_NULL) === false) {
        return null;
    }

    $index = null;
    foreach (array_filter($matches) as $key => $value) {
        if (is_numeric($key) || !str_starts_with($key, '_')) {
            continue;
        }
        $i = substr($key, 1);
        if ($index === null && is_numeric($i)) {
            $index = (int)$i;
            continue;
        }
        if ($index === null || empty($value) || !str_starts_with($key, "_{$index}")) {
            continue;
        }

        $attributes[str_replace("_{$index}_", '', $key)] = $value;
    }

    return $index;
}