protected function add_course_terms( $course_id, $raw_terms ) {

		$taxes = array(
			'course_cat'        => 'categories',
			'course_difficulty' => 'difficulty',
			'course_tag'        => 'tags',
			'course_track'      => 'tracks',
		);

		foreach ( $taxes as $tax => $key ) {

			if ( ! empty( $raw_terms[ $key ] ) && is_array( $raw_terms[ $key ] ) ) {

				// We can only have one difficulty at a time.
				$append = ( 'difficulty' === $key ) ? false : true;

				$terms = array();

				// Find term id or create it.
				foreach ( $raw_terms[ $key ] as $term_name ) {

					if ( empty( $term_name ) ) {
						continue;
					}

					$term_id = $this->get_term_id( $term_name, $tax );
					if ( $term_id ) {
						$terms[] = $term_id;
					}
				}

				wp_set_post_terms( $course_id, $terms, $tax, $append );

			}
		}

	}