public function get_sequential_number_store() {
		$reset_number_yearly = isset( $this->settings['reset_number_yearly'] ) ? true : false;
		$method              = WPO_WCPDF()->settings->get_sequential_number_store_method();
		$now                 = new \WC_DateTime( 'now', new \DateTimeZone( 'UTC' ) ); // for settings callback
	
		// reset: on
		if ( $reset_number_yearly ) {
			if ( ! ( $date = $this->get_date() ) ) {
				$date = $now;
			}
			
			// for yearly reset debugging only
			if ( apply_filters( 'wpo_wcpdf_enable_yearly_reset_debug', false ) ) {
				$date = new \WC_DateTime( '1st January Next Year' );
			}
			
			$store_name   = $this->get_sequential_number_store_name( $date, $method, $reset_number_yearly );
			$number_store = new Sequential_Number_Store( $store_name, $method );	
	
			if ( $number_store->is_new ) {
				$number_store->set_next( apply_filters( 'wpo_wcpdf_reset_number_yearly_start', 1, $this ) );
			}
		// reset: off
		} else {
			$store_name   = $this->get_sequential_number_store_name( $now, $method, $reset_number_yearly );
			$number_store = new Sequential_Number_Store( $store_name, $method );
		}
	
		return $number_store;
	}

	/**
	 * Get the name of the Sequential Number Store, based on the date ('now' or 'document date')
	 * and whether the number should be reset yearly. When the number is reset yearly, numbered
	 * stores are used for non-current years, adding the year as the suffix
	 * 
	 * @return string $number_store_name
	 */
	public function get_sequential_number_store_name( $date, $method, $reset_number_yearly ) {
		$store_base_name    = $this->order ? apply_filters( 'wpo_wcpdf_document_sequential_number_store', "{$this->slug}_number", $this ) : "{$this->slug}_number";
		$default_table_name = $this->get_number_store_table_default_name( $store_base_name, $method );
		$current_store_year = $this->get_number_store_year( $default_table_name );
		$requested_year     = intval( $date->date_i18n( 'Y' ) );

		// if we don't reset the number yearly, the store name is always the same
		if ( ! $reset_number_yearly ) {
			$number_store_name = $store_base_name;
		} else {
			// if the current store year doesn't match the year requested, check if we need to retire the store
			// (meaning that we have entered a new year)
			if( $requested_year !== $current_store_year ) {
				$current_store_year = $this->maybe_retire_number_store( $date, $store_base_name, $method );
			}

			// If it's a non-current year (future or past), append the year to the store name, otherwise use default
			if( $requested_year !== $current_store_year ) {
				$number_store_name = "{$store_base_name}_{$requested_year}";
			} else {
				$number_store_name = $store_base_name;
			}
		}
	
		return apply_filters( "wpo_wcpdf_{$this->slug}_number_store_name", $number_store_name, $store_base_name, $date, $method, $this );
	}

	/**
	 * Get the default table name of the Sequential Number Store
	 * @param  string $store_base_name
	 * @param  string $method
	 * 
	 * @return string $table_name
	 */
	public function get_number_store_table_default_name( $store_base_name, $method ) {
		global $wpdb;
		return apply_filters( "wpo_wcpdf_number_store_table_name", "{$wpdb->prefix}wcpdf_{$store_base_name}", $store_base_name, $method );
	}

	/**
	 * Takes care of the rotation of database tables for the number store, used when 'reset yearly' is enabled:
	 * 
	 * The table name for the current year is _always_ "{$wpdb->prefix}wcpdf_{$store_base_name}", e.g. wp_wcpdf_invoice_number
	 * 
	 * when a year lapses, the existing table ('last year') is 'retired' by renaming it with the year appended,
	 * e.g. wp_wcpdf_invoice_number_2021 (when the current/new year is 2022). If there was a table for the new year,
	 * this will be renamed to the default store name (e.g. wp_wcdpdf_invoice_number)
	 * 
	 * returns requested year if any error occurs, so that the current store table will be used
	 * 
	 * @return int $year year of the current number store
	 */
	public function maybe_retire_number_store( $date, $store_base_name, $method ) {
		global $wpdb;
		$was_showing_errors = $wpdb->hide_errors(); // if we encounter errors, we'll log them instead
		
		$default_table_name = $this->get_number_store_table_default_name( $store_base_name, $method );
		$now                = new \WC_DateTime( 'now', new \DateTimeZone( 'UTC' ) );
		
		// for yearly reset debugging only
		if ( apply_filters( 'wpo_wcpdf_enable_yearly_reset_debug', false ) ) {
			$now = new \WC_DateTime( '1st January Next Year' );
		}
		
		$current_year       = intval( $now->date_i18n( 'Y' ) );
		$current_store_year = intval( $this->get_number_store_year( $default_table_name ) );
		$requested_year     = intval( $date->date_i18n( 'Y' ) );

		// nothing to retire if requested year matches current store year or if current store year is not in the past
		if ( empty( $current_store_year ) || $requested_year == $current_store_year || ! ( $current_store_year < $current_year ) ) {
			return $current_store_year;
		}
		
		// current store year is in the past: rename table so that we can replace it with the current year

		$retired_table_name      = "{$default_table_name}_{$current_store_year}";
		$current_year_table_name = "{$default_table_name}_{$current_year}";

		// first, remove last year if it already exists
		$retired_exists = $wpdb->get_var( "SHOW TABLES LIKE '{$retired_table_name}'" ) == $retired_table_name; 
		if( $retired_exists ) {
			$table_removed = $wpdb->query( "DROP TABLE IF EXISTS {$retired_table_name}" );

			if( ! $table_removed ) {
				wcpdf_log_error( sprintf( 'An error occurred while trying to remove the duplicate number store %s: %s', $retired_table_name, $wpdb->last_error ) );
				return $requested_year;
			}
		}

		// rename current to last year
		$default_exists = $wpdb->get_var( "SHOW TABLES LIKE '{$default_table_name}'" ) == $default_table_name;
		if( $default_exists ) {
			$table_renamed = $wpdb->query( "ALTER TABLE {$default_table_name} RENAME {$retired_table_name}" );
			
			if( ! $table_renamed ) {
				wcpdf_log_error( sprintf( 'An error occurred while trying to rename the number store from %s to %s: %s', $default_table_name, $retired_table_name, $wpdb->last_error ) );
				return $requested_year;
			}
		}
		
		// if the current year table name already exists (created earlier as a 'future' year), rename that to default
		$current_year_exists = $wpdb->get_var( "SHOW TABLES LIKE '{$current_year_table_name}'" ) == $current_year_table_name;
		if( $current_year_exists ) {
			$table_renamed = $wpdb->query( "ALTER TABLE {$current_year_table_name} RENAME {$default_table_name}" );

			if( ! $table_renamed ) {
				wcpdf_log_error( sprintf( 'An error occurred while trying to rename the number store from %s to %s: %s', $current_year_table_name, $default_table_name, $wpdb->last_error ) );
				return $requested_year;
			}
		}

		if( $was_showing_errors ) {
			$wpdb->show_errors();
		}

		// current store year has been updated to current year, returning this means no year suffix has to be used
		return $current_year;
	}

	/**
	 * Gets the year from the last row of a number store table
	 * @param  string $table_name
	 * 
	 * @return string
	 */
	public function get_number_store_year( $table_name ) {
		global $wpdb;
		$was_showing_errors = $wpdb->hide_errors(); // if we encounter errors, we'll log them instead

		$current_year = date_i18n( 'Y' );
		
		// for yearly reset debugging only
		if ( apply_filters( 'wpo_wcpdf_enable_yearly_reset_debug', false ) ) {
			$next_year    = new \WC_DateTime( '1st January Next Year' );
			$current_year = intval( $next_year->date_i18n( 'Y' ) );
		}
		
		$table_exists = $wpdb->get_var( "SHOW TABLES LIKE '{$table_name}'") == $table_name; 
		if( $table_exists ) {
			// get year for the last row
			$year = $wpdb->get_var( "SELECT YEAR(date) FROM {$table_name} ORDER BY id DESC LIMIT 1" );
			// default to current year if no results
			if( ! $year ) {
				$year = $current_year;
				// if we don't get a result, this could either mean there's an error,
				// OR that the first number simply has not been created yet (=no rows)
				// we only log when there's an actual error
				if( ! empty( $wpdb->last_error ) ) {
					wcpdf_log_error( sprintf( 'An error occurred while trying to get the current year from the %s table: %s', $table_name, $wpdb->last_error ) );
				}
			}
		} else {
			$year = $current_year;
		}

		if( $was_showing_errors ) {
			$wpdb->show_errors();
		}

		return intval( $year );
	}

	protected function add_filters( $filters ) {
		foreach ( $filters as $filter ) {
			$filter = $this->normalize_filter_args( $filter );
			add_filter( $filter['hook_name'], $filter['callback'], $filter['priority'], $filter['accepted_args'] );
		}
	}

	protected function remove_filters( $filters ) {
		foreach ( $filters as $filter ) {
			$filter = $this->normalize_filter_args( $filter );
			remove_filter( $filter['hook_name'], $filter['callback'], $filter['priority'] );
		}
	}

	protected function normalize_filter_args( $filter ) {
		$filter = array_values( $filter ); 
		$hook_name = $filter[0];
		$callback = $filter[1];
		$priority = isset( $filter[2] ) ? $filter[2] : 10;
		$accepted_args = isset( $filter[3] ) ? $filter[3] : 1;
		return compact( 'hook_name', 'callback', 'priority', 'accepted_args' );
	}

}

endif; // class_exists