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/******************************************************************************/
/* Metaboxes */

function add_banner_link_metabox(){
    $id = "link";
    $title = "Link do Banner";
    $callback = "add_banner_link_inner_metabox";
    $post_types = array("slide");

    foreach($post_types as $post_type) {
        add_meta_box(
            $id,
            $title,
            $callback,
            $post_type
        );
    }
}

add_action('add_meta_boxes', 'add_banner_link_metabox');

function add_banner_link_inner_metabox($post) {

  wp_nonce_field('add_banner_link_inner_metabox', 'add_banner_link_inner_metabox_nonce');

  $value = get_post_meta($post->ID, 'link', true);

  echo '<label for="link">';
       _e( "Link do Banner", 'textdomain' );
  echo '</label> ';
  echo '<input type="text" id="link" name="link" value="' . esc_attr($value) . '" size="44" />';

}

function add_banner_link_save_postdata( $post_id ) {

  if ( ! isset( $_POST['add_banner_link_inner_metabox_nonce'] ) )
    return $post_id;

  $nonce = $_POST['add_banner_link_inner_metabox_nonce'];

  if ( ! wp_verify_nonce( $nonce, 'add_banner_link_inner_metabox' ) )
      return $post_id;

  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) 
      return $post_id;

  if ( 'page' == $_POST['superbanner'] ) {

    if ( ! current_user_can( 'edit_page', $post_id ) )
        return $post_id;
  
  } else {

    if ( ! current_user_can( 'edit_post', $post_id ) )
        return $post_id;
  }

  $mydata = sanitize_text_field( $_POST['link'] );
  update_post_meta( $post_id, 'link', $mydata );
}

add_action( 'save_post', 'add_banner_link_save_postdata' );