^^&&^^

Edit File: class-kkart-coupon-data-store-interface.php

<?php
/**
 * Coupon Data Store Interface
 *
 * @version 3.0.0
 * @package Kkart\Interfaces
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * KKART Coupon Data Store Interface
 *
 * Functions that must be defined by coupon store classes.
 *
 * @version  3.0.0
 */
interface KKART_Coupon_Data_Store_Interface {
	/**
	 * Increase usage count for current coupon.
	 *
	 * @param KKART_Coupon $coupon Coupon object.
	 * @param string    $used_by Either user ID or billing email.
	 */
	public function increase_usage_count( &$coupon, $used_by = '' );

/**
	 *  Decrease usage count for current coupon.
	 *
	 * @param KKART_Coupon $coupon Coupon object.
	 * @param string    $used_by Either user ID or billing email.
	 */
	public function decrease_usage_count( &$coupon, $used_by = '' );

/**
	 * Get the number of uses for a coupon by user ID.
	 *
	 * @param KKART_Coupon $coupon Coupon object.
	 * @param int       $user_id User ID.
	 * @return int
	 */
	public function get_usage_by_user_id( &$coupon, $user_id );

/**
	 * Return a coupon code for a specific ID.
	 *
	 * @param int $id Coupon ID.
	 * @return string Coupon Code.
	 */
	public function get_code_by_id( $id );

/**
	 * Return an array of IDs for for a specific coupon code.
	 * Can return multiple to check for existence.
	 *
	 * @param string $code Coupon code.
	 * @return array Array of IDs.
	 */
	public function get_ids_by_code( $code );
}