*
	 * @since 1.0.0-beta.1
	 * @since 1.0.0-beta.7 `access_opens_date`, `access_closes_date`, `enrollment_opens_date`, `enrollment_closes_date`
	 *                     treated in @see `update_additional_object_fields()` method so to better handle the update of the
	 *                     course's properties `time_period` and `enrollment_period` whose values are derived from them and need to be
	 *                     passed to `$course->set_bulk()` only if they differ from their current values, otherwise we'd get a WP_Error
	 *                     which the consumer cannot avoid having no direct control on those properties.
	 *                     Made `access_opens_date`, `access_closes_date`, `enrollment_opens_date`, `enrollment_closes_date` nullable.
	 * @since 1.0.0-beta.8 Renamed `sales_page_page_type` and `sales_page_page_url` properties, respectively to `sales_page_type` and `sales_page_url` according to the specs.
	 * @since 1.0.0-beta.9 Added `llms_rest_pre_insert_course` filter hook.
	 *
	 * @param WP_REST_Request $request Request object.
	 * @return array|WP_Error Array of llms post args or WP_Error.
	 */
	protected function prepare_item_for_database( $request ) {

		$prepared_item = parent::prepare_item_for_database( $request );
		$schema        = $this->get_item_schema();

		// Course Audio embed URL.
		if ( ! empty( $schema['properties']['audio_embed'] ) && isset( $request['audio_embed'] ) ) {
			$prepared_item['audio_embed'] = $request['audio_embed'];
		}

		// Course Video embed URL.
		if ( ! empty( $schema['properties']['video_embed'] ) && isset( $request['video_embed'] ) ) {
			$prepared_item['video_embed'] = $request['video_embed'];
		}

		// Video tile.
		if ( ! empty( $schema['properties']['video_tile'] ) && isset( $request['video_tile'] ) ) {
			$prepared_item['tile_featured_video'] = empty( $request['video_tile'] ) ? 'no' : 'yes';
		}

		// Capacity enabled.
		if ( ! empty( $schema['properties']['capacity_enabled'] ) && isset( $request['capacity_enabled'] ) ) {
			$prepared_item['enable_capacity'] = empty( $request['capacity_enabled'] ) ? 'no' : 'yes';
		}

		// Capacity message.
		if ( ! empty( $schema['properties']['capacity_message'] ) && isset( $request['capacity_message'] ) ) {
			if ( is_string( $request['capacity_message'] ) ) {
				$prepared_item['capacity_message'] = $request['capacity_message'];
			} elseif ( isset( $request['capacity_message']['raw'] ) ) {
				$prepared_item['capacity_message'] = $request['capacity_message']['raw'];
			}
		}

		// Capacity limit.
		if ( ! empty( $schema['properties']['capacity_limit'] ) && isset( $request['capacity_limit'] ) ) {
			$prepared_item['capacity'] = $request['capacity_limit'];
		}

		// Restricted message.
		if ( ! empty( $schema['properties']['restricted_message'] ) && isset( $request['restricted_message'] ) ) {
			if ( is_string( $request['restricted_message'] ) ) {
				$prepared_item['content_restricted_message'] = $request['restricted_message'];
			} elseif ( isset( $request['restricted_message']['raw'] ) ) {
				$prepared_item['content_restricted_message'] = $request['restricted_message']['raw'];
			}
		}

		// Length.
		if ( ! empty( $schema['properties']['length'] ) && isset( $request['length'] ) ) {
			if ( is_string( $request['length'] ) ) {
				$prepared_item['length'] = $request['length'];
			} elseif ( isset( $request['length']['raw'] ) ) {
				$prepared_item['length'] = $request['length']['raw'];
			}
		}

		// Sales page.
		if ( ! empty( $schema['properties']['sales_page_type'] ) && isset( $request['sales_page_type'] ) ) {
			$prepared_item['sales_page_content_type'] = $request['sales_page_type'];
		}

		if ( ! empty( $schema['properties']['sales_page_page_id'] ) && isset( $request['sales_page_page_id'] ) ) {
			$sales_page = get_post( $request['sales_page_page_id'] );
			if ( $sales_page && is_a( $sales_page, 'WP_Post' ) ) {
				$prepared_item['sales_page_content_page_id'] = $request['sales_page_page_id']; // maybe allow only published pages?
			} else {
				$prepared_item['sales_page_content_page_id'] = 0;
			}
		}

		if ( ! empty( $schema['properties']['sales_page_url'] ) && isset( $request['sales_page_url'] ) ) {
			$prepared_item['sales_page_content_url'] = $request['sales_page_url'];