A function to wrap a string with "A" HTML tag if it's a link

functions.php

<?php

function wrap_with_link( $string ) {
    /**
     * The Regex:
     *
     * From the start of the string we look for http or https protocols or just "://"
     * After that we look for one or more not-whitespace string plus dot in the end
     * After that we look for one not-whitespace-with-2-or-3 string
     * In the end we look for one '?' or '/' character and than zero or more not-whitespace string
     */
    $regex = '/^(?:(?:http(?:s)?)?:\/\/)?(?:[\S]+\.{1})+(?:[\S]{2,3}){1}(?:[?\/]{1}[\S]*)*$/i';

    if ( preg_match( $regex, $string ) ) {
        // The function 'esc_url' is from WordPress: you can remove it or create a URL parser when using it outside WP
        return '<a href="' . esc_url( $string ) . '" target="_blank">' . $string . '</a>';
    }

    return $string;
}