class Tags

class Tags {
    
    /**
     * Explodes a string of tags into an array.
     *
     * @param string $tags
     *   A string to explode.
     *
     * @return array
     *   An array of tags.
     */
    public static function explode($tags) {
        // This regexp allows the following types of user input:
        // this, "somecompany, llc", "and ""this"" w,o.rks", foo bar
        $regexp = '%(?:^|,\\ *)("(?>[^"]*)(?>""[^"]* )*"|(?: [^",]*))%x';
        preg_match_all($regexp, $tags, $matches);
        $typed_tags = array_unique($matches[1]);
        $tags = [];
        foreach ($typed_tags as $tag) {
            // If a user has escaped a term (to demonstrate that it is a group,
            // or includes a comma or quote character), we remove the escape
            // formatting so to save the term into the database as the user intends.
            $tag = trim(str_replace('""', '"', preg_replace('/^"(.*)"$/', '\\1', $tag)));
            if ($tag != "") {
                $tags[] = $tag;
            }
        }
        return $tags;
    }
    
    /**
     * Encodes a tag string, taking care of special cases like commas and quotes.
     *
     * @param string $tag
     *   A tag string.
     *
     * @return string
     *   The encoded string.
     */
    public static function encode($tag) {
        if (strpos($tag, ',') !== FALSE || strpos($tag, '"') !== FALSE) {
            return '"' . str_replace('"', '""', $tag) . '"';
        }
        return $tag;
    }
    
    /**
     * Implodes an array of tags into a string.
     *
     * @param array $tags
     *   An array of tags.
     *
     * @return string
     *   The imploded string.
     */
    public static function implode($tags) {
        $encoded_tags = [];
        foreach ($tags as $tag) {
            $encoded_tags[] = self::encode($tag);
        }
        return implode(', ', $encoded_tags);
    }

}