private static function update_quiz( $quiz_data, $lesson, $course_id = 0 ) {

		$res = array_merge(
			$quiz_data,
			array(
				'orig_id' => $quiz_data['id'],
			)
		);

		// Confirm the current user can edit the course this quiz belongs to, independent of earlier checks.
		$authorized_course_id = $course_id ? absint( $course_id ) : absint( $lesson->get( 'parent_course' ) );
		if ( $authorized_course_id && ! current_user_can( 'edit_course', $authorized_course_id ) ) {
			// Translators: %s = Quiz post id.
			$res['error'] = sprintf( esc_html__( 'Unable to update quiz "%s". You are not allowed to edit the parent course.', 'lifterlms' ), $quiz_data['id'] );
			return $res;
		}

		// Create a quiz.
		if ( self::is_temp_id( $quiz_data['id'] ) ) {

			$quiz = new LLMS_Quiz(
				'new',
				array(
					'post_title' => isset( $quiz_data['title'] ) ? $quiz_data['title'] : __( 'New Quiz', 'lifterlms' ),
				)
			);

			// Update existing quiz.
		} else {

			$quiz = llms_get_post( $quiz_data['id'] );

			// Verify the quiz belongs to this course.
			if ( $course_id && $quiz && is_a( $quiz, 'LLMS_Quiz' ) ) {
				$parent = self::get_object_parent_course_id( $quiz->get( 'id' ) );
				if ( $parent && absint( $parent ) !== absint( $course_id ) ) {
					// Translators: %s = Quiz post id.
					$res['error'] = sprintf( esc_html__( 'Unable to update quiz "%s". Invalid quiz ID.', 'lifterlms' ), $quiz_data['id'] );
					return $res;
				}
				if ( ! $parent && ! current_user_can( 'edit_post', $quiz->get( 'id' ) ) ) {
					$res['error'] = sprintf( esc_html__( 'Unable to update quiz "%s". Invalid quiz ID.', 'lifterlms' ), $quiz_data['id'] );
					return $res;
				}
			}
		}

		$lesson->set( 'quiz', $quiz->get( 'id' ) );
		$lesson->set( 'quiz_enabled', 'yes' );

		// We don't have a proper quiz to work with...
		if ( empty( $quiz ) || ! is_a( $quiz, 'LLMS_Quiz' ) ) {

			// Translators: %s = Quiz post id.
			$res['error'] = sprintf( esc_html__( 'Unable to update quiz "%s". Invalid quiz ID.', 'lifterlms' ), $quiz_data['id'] );

		} else {

			// Return the real ID (important when creating a new quiz).
			$res['id'] = $quiz->get( 'id' );

			/**
			 * If the parent lesson was just created the lesson will have a temp id
			 * replace it with the newly created lessons's real ID.
			 */
			if ( ! isset( $quiz_data['lesson_id'] ) || self::is_temp_id( $quiz_data['lesson_id'] ) ) {
				$quiz_data['lesson_id'] = $lesson->get( 'id' );
			}

			$properties = array_merge(
				array_keys( $quiz->get_properties() ),
				array(
					// phpcs:ignore -- commented out code
					// 'content',
					'status',
					'title',
				)
			);

			// Update all updatable properties.
			// Never trust a client-supplied lesson_id; the quiz must belong to the authorized lesson.
			foreach ( $properties as $prop ) {
				if ( isset( $quiz_data[ $prop ] ) && 'lesson_id' !== $prop ) {
					$quiz->set( $prop, $quiz_data[ $prop ] );
				}
			}
			$quiz->set( 'lesson_id', $lesson->get( 'id' ) );
			$res['lesson_id'] = $lesson->get( 'id' );

			// Include permalink and slug in the response so the builder can update the model.
			$res['permalink'] = get_permalink( $quiz->get( 'id' ) );
			$res['name']      = $quiz->get( 'name' );

			if ( isset( $quiz_data['questions'] ) && is_array( $quiz_data['questions'] ) ) {
				$res['questions'] = self::update_questions( $quiz_data['questions'], $quiz, $course_id );
			}

			// Update all custom fields.
			self::update_custom_schemas( 'quiz', $quiz, $quiz_data );

		}

		return $res;
	}