add_action( 'wpf_meta_box_content', 'cea_wpf_ld_meta_box', 40, 2 );

function cea_wpf_ld_meta_box( $post, $settings ) {

    if($post->post_type != 'sfwd-lessons')
        return;

    echo '<p><label for="link_tag_lesson"><small>Mark lesson complete when this tag is applied:</small></label>';

    wpf_render_tag_multiselect( $settings['link_tag_lesson'], 'wpf-settings', 'link_tag_lesson', null, false, 'Select Tag', 1 );

    echo '</p>';


}

add_action( 'wpf_tags_modified', 'cea_mark_lessons_complete', 10, 2 );

function cea_mark_lessons_complete( $user_id, $user_tags ) {

    $lessons = get_posts( array(
        'post_type'  => 'sfwd-lessons',
        'nopaging'   => true,
        'meta_query' => array(
            array(
                'key'     => 'wpf-settings-learndash',
                'compare' => 'EXISTS'
            ),
        ),
        'fields'     => 'ids'
    ) );

    foreach( $lessons as $lesson_id ) {

        $settings = get_post_meta( $lesson_id, 'wpf-settings-learndash', true );

        if ( empty( $settings ) || empty( $settings['link_tag_lesson'] ) ) {
            continue;
        }

        $tag_id = $settings['link_tag_lesson'][0];

        if ( in_array( $tag_id, $user_tags ) ) {

            // Prevent "lesson complete" tag from being applied
            remove_action( 'learndash_lesson_completed', array( wp_fusion()->integrations->learndash, 'apply_tags_learndash_complete' ) );

            // Mark lesson complete
            learndash_process_mark_complete( $user_id, $lesson_id );

        }

    }

}