update tags on frontend

//on the fronted, displaying to user, above post, maybe in single.php

<form id="cadastro" name="cadastro" method="post" action="" enctype="multipart/form-data">
<label for="ca_tags">Tags:</label>
<input type="text" id="ca_tags" name="ca_tags" maxlength="254" />

<small>(comma separated)</small>

<input type="hidden" name="page" id="page" value="<?php echo $post->ID; ?>"/>
<?php wp_nonce_field('new-tag','tag-nonce'); ?>
<input type="submit" value="Enviar anúncio para aprovação" />
</form>

//on top of file, the same single.php

if(!empty($_POST) && wp_verify_nonce($_POST['tag-nonce'],'new-tag')) {

if($_POST['ca_tags']){$tags = array('tags' => $_POST['ca_tags']);}
    else{$tags = array('tags' => '');}

wp_set_post_terms($post->ID, $tags, 'tags' );
}