Camel case to underscore with unicode support

camelCaseToUnderscore.php

/**
 * @param string
 * @return string
 */
function camelCaseToUnderscore($string)
{
    // Default patterm
    $pattern = array('#(?<=(?:[A-Z]))([A-Z]+)([A-Z][A-z])#', '#(?<=(?:[a-z0-9]))([A-Z])#');

    // Check fo unicode support
    $unicodeSupportEnabled = (@preg_match('/\pL/u', 'a')) ? true : false;

    if ($unicodeSupportEnabled) {
        // Change pattern for unicode support
        $pattern = array('#(?<=(?:\p{Lu}))(\p{Lu}\p{Ll})#','#(?<=(?:\p{Ll}|\p{Nd}))(\p{Lu})#');
    }
    return preg_replace_callback(
        $pattern,
        function ($match) {
            return '_' . strtolower($match[0]);
        },
        lcfirst($string)
    );
}