private static function update_questions( $questions, $parent, $course_id = 0 ) {

		$res = array();

		foreach ( $questions as $q_data ) {

			$ret = array_merge(
				$q_data,
				array(
					'orig_id' => $q_data['id'],
				)
			);

			// Remove temp id if we have one so we'll create a new question.
			if ( self::is_temp_id( $q_data['id'] ) ) {
				unset( $q_data['id'] );
			} else {
				// Verify the question belongs to this course.
				$q_parent = $course_id ? self::get_object_parent_course_id( absint( $q_data['id'] ) ) : 0;
				if ( $q_parent && absint( $q_parent ) !== absint( $course_id ) ) {
					// Translators: %s = Question post id.
					$ret['error'] = sprintf( esc_html__( 'Unable to update question "%s". Invalid question ID.', 'lifterlms' ), $q_data['id'] );
					array_push( $res, $ret );
					continue;
				}
				if ( $course_id && ! $q_parent && ! current_user_can( 'edit_post', absint( $q_data['id'] ) ) ) {
					// Translators: %s = Question post id.
					$ret['error'] = sprintf( esc_html__( 'Unable to update question "%s". Invalid question ID.', 'lifterlms' ), $q_data['id'] );
					array_push( $res, $ret );
					continue;
				}
			}

			// Remove choices because we'll add them individually after creation.
			$choices = ( isset( $q_data['choices'] ) && is_array( $q_data['choices'] ) ) ? $q_data['choices'] : false;
			unset( $q_data['choices'] );

			// Remove child questions if it's a question group.
			$questions = ( isset( $q_data['questions'] ) && is_array( $q_data['questions'] ) ) ? $q_data['questions'] : false;
			unset( $q_data['questions'] );

			$question_id = $parent->questions()->update_question( $q_data );

			if ( ! $question_id ) {

				// Translators: %s = Question post id.
				$ret['error'] = sprintf( esc_html__( 'Unable to update question "%s". Invalid question ID.', 'lifterlms' ), $q_data['id'] );

			} else {

				$ret['id'] = $question_id;

				$question = $parent->questions()->get_question( $question_id );

				/**
				 * When saving a question, make sure that it has a question type set
				 * otherwise set it by default to `'choice'`.
				 */
				if ( ! $question->get( 'question_type', true ) ) {
					$question->set( 'question_type', 'choice' );
				}

				if ( $choices ) {

					$ret['choices'] = array();

					foreach ( $choices as $c_data ) {

						$choice_res = array_merge(
							$c_data,
							array(
								'orig_id' => $c_data['id'],
							)
						);

						unset( $c_data['question_id'] );

						// Remove the temp ID so that we create it if it's new.
						if ( self::is_temp_id( $c_data['id'] ) ) {
							unset( $c_data['id'] );
						}

						$choice_id = $question->update_choice( $c_data );
						if ( ! $choice_id ) {
							// Translators: %s = Question choice ID.
							$choice_res['error'] = sprintf( esc_html__( 'Unable to update choice "%s". Invalid choice ID.', 'lifterlms' ), $c_data['id'] );
						} else {
							$choice_res['id'] = $choice_id;

							$choice_media_id = isset( $c_data['choice']['id'] ) ? absint( $c_data['choice']['id'] ) : 0;
							// Only bind the protected-media meta when the current user is allowed to edit that specific media object.
							if ( $choice_media_id && current_user_can( 'edit_post', $choice_media_id ) ) {
								// The quiz IDs are needed for later verification of access by the protected media filters.
								$quiz_ids = get_post_meta( $choice_media_id, '_llms_quiz_id', true );
								if ( ! is_array( $quiz_ids ) ) {
									$quiz_ids = array();
								}
								$quiz_id = $parent->get( 'parent_id' ) ? $parent->get( 'parent_id' ) : $parent->get( 'id' );
								if ( ! in_array( $quiz_id, $quiz_ids ) ) {
									$quiz_ids[] = $quiz_id;
								}
								update_post_meta( $choice_media_id, '_llms_quiz_id', $quiz_ids );
							}
						}

						array_push( $ret['choices'], $choice_res );

					}
				} elseif ( $questions ) {

					$ret['questions'] = self::update_questions( $questions, $question, $course_id );

				}
			}

			array_push( $res, $ret );

		}

		return $res;
	}