feat: add Coupon base class

src/Coupons/Coupon.php

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wearepixel\Cart\Coupons;
+
+use Wearepixel\Cart\CartCondition;
+use Wearepixel\Cart\Contracts\CartConditionable;
+use Wearepixel\Cart\Exceptions\InvalidCouponException;
+
+abstract class Coupon implements CartConditionable
+{
+    protected string $code;
+
+    protected string $value;
+
+    protected string $target = 'subtotal';
+
+    protected ?float $minimum = null;
+
+    protected ?float $maximum = null;
+
+    abstract public function isValid(): bool;
+
+    public function getCode(): string
+    {
+        return $this->code;
+    }
+
+    public function toCondition(): CartCondition
+    {
+        if (! $this->isValid()) {
+            throw new InvalidCouponException("Coupon [{$this->code}] is not valid.");
+        }
+
+        $data = [
+            'name'   => $this->code,
+            'type'   => 'coupon',
+            'value'  => $this->value,
+            'target' => $this->target,
+        ];
+
+        if ($this->minimum !== null) {
+            $data['minimum'] = $this->minimum;
+        }
+
+        if ($this->maximum !== null) {
+            $data['maximum'] = $this->maximum;
+        }
+
+        return new CartCondition($data);
+    }
+}