Php Function to replace the keywords from text

php_keyword_replacer.php

<?php
public function replace_shortcode( $args, $body ) {

    $tags =  array(
        'email' 	=> "",
        'firstname' 	=> "",
        'lastname' => "",
    );
    $tags = array_merge( $tags, $args );

    extract( $tags );

    $tags 	= array( '{email}',
                    '{firstname}',
                    '{lastname}',
                    );

    $values  = array(   $email, 
                        $firstname ,
                        $lastname,
    );

    $message = str_replace($tags, $values, $body);	

    $message = nl2br($message);
    $message = htmlspecialchars_decode($message,ENT_QUOTES);

    return $message;
}