private static function update_quiz( $quiz_data, $lesson ) {

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

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

			$quiz = new LLMS_Quiz( 'new' );

			// Update existing quiz.
		} else {

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

		}

		$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.
			foreach ( $properties as $prop ) {
				if ( isset( $quiz_data[ $prop ] ) ) {
					$quiz->set( $prop, $quiz_data[ $prop ] );
				}
			}

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

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

		}

		return $res;

	}