Provide a way to check if a coupon is valid for a customer/user.

[simeon-smith]

What are you trying to do?
I need to check if a coupon code is valid for a customer/user.

What's your proposed solution?
Provide a twig method either on the customer/user to check a coupon codes validity or provide a way on a coupon to pass a customer/users id or email to check if the coupon is valid for that.

[simeon-smith]

I was able to create a module that does this using a Twig function. This is what that twig extension looks like. @lukeholder

<?php

/**
 * Is Coupon Valid module for Craft CMS 3.x
 *
 * Checks if a commerce coupon is valid. Can be used to check if the coupon is valid for a specific customer or email.
 *
 * @link      https://uxiliary.com
 * @copyright Copyright (c) 2020 Simeon Smith
 */

namespace modules\iscouponvalidmodule\twigextensions;

use modules\iscouponvalidmodule\IsCouponValidModule;
use craft\commerce\records\CustomerDiscountUse as CustomerDiscountUseRecord;
use craft\commerce\records\EmailDiscountUse as EmailDiscountUseRecord;
use craft\commerce\Plugin as Commerce;

use Craft;

use Twig\Extension\AbstractExtension;
use Twig\TwigFilter;
use Twig\TwigFunction;

/**
 * Twig can be extended in many ways; you can add extra tags, filters, tests, operators,
 * global variables, and functions. You can even extend the parser itself with
 * node visitors.
 *
 * http://twig.sensiolabs.org/doc/advanced.html
 *
 * @author    Simeon Smith
 * @package   IsCouponValidModule
 * @since     1.0.0
 */
class IsCouponValidModuleTwigExtension extends AbstractExtension
{
    // Public Methods
    // =========================================================================

    /**
     * Returns the name of the extension.
     *
     * @return string The extension name
     */
    public function getName()
    {
        return 'IsCouponValidModule';
    }

    /**
     * Returns an array of Twig filters, used in Twig templates via:
     *
     *      {{ 'something' | someFilter }}
     *
     * @return array
     */
    public function getFilters()
    {
        return [];
    }

    /**
     * Returns an array of Twig functions, used in Twig templates via:
     *
     *      {% set this = someFunction('something') %}
     *
     * @return array
     */
    public function getFunctions()
    {
        return [
            new TwigFunction('isDiscountValid', [$this, 'isDiscountValid']),
        ];
    }

    /**
     * Our function called via Twig; it can do anything you want
     *
     * @param null $text
     *
     * @return string
     */
    public function isDiscountValid($discountId, $customerId = null)
    {
        if (is_null($customerId)) {
            $customer = Commerce::getInstance()->getCustomers()->getCustomer();
            $customerId = $customer->id;
            $email = $customer->getEmail();
        } else {
            $customer = Commerce::getInstance()->getCustomers()->getCustomerById($customerId);
            $email = $customer->getEmail();
        }

        $discount = Commerce::getInstance()->getDiscounts()->getDiscountById($discountId);

        $discountValid = true;

        if ($discount->perUserLimit) {
            $customerDiscountUseRecord = CustomerDiscountUseRecord::find()->where(['[[customerId]]' => $customer->id, '[[discountId]]' => $discount->id])->select(["discountId", "customerId", "uses"])->asArray()->all();
            if (!is_null($customerDiscountUseRecord) && count($customerDiscountUseRecord) > 0) {
                foreach ($customerDiscountUseRecord as $record) {
                    if ($record["uses"] >= $discount->perUserLimit) {
                        $discountValid = false;
                    }
                }
            }
        }

        if ($discount->perEmailLimit) {
            $emailDiscountUseRecord = EmailDiscountUseRecord::find()->where(['[[email]]' => $email, '[[discountId]]' => $discount->id])->select(["discountId", "email", "uses"])->asArray()->all();

            if (!is_null($emailDiscountUseRecord) && count($emailDiscountUseRecord) > 0) {
                foreach ($emailDiscountUseRecord as $record) {
                    if ($record["uses"] >= $discount->perEmailLimit) {
                        $discountValid = false;
                    }
                }
            }
        }



        return $discountValid;
    }
}