feat(coupons): add coupon service and result value object

src/Services/CouponService.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace Bazaar\Services;
+
+use Bazaar\Repositories\CouponRepository;
+
+final class CouponService
+{
+    public function __construct(private readonly CouponRepository $coupons)
+    {
+    }
+
+    public function evaluate(string $code, int $subtotalCents, ?string $now = null): CouponResult
+    {
+        $coupon = $this->coupons->findByCode($code);
+        if ($coupon === null) {
+            return CouponResult::fail(CouponResult::notFound);
+        }
+
+        $now ??= gmdate('c');
+
+        if ((int) $coupon['isActive'] !== 1) {
+            return CouponResult::fail(CouponResult::inactive, $coupon);
+        }
+        if ($coupon['startsAt'] !== null && $coupon['startsAt'] !== '' && $now < $coupon['startsAt']) {
+            return CouponResult::fail(CouponResult::notStarted, $coupon);
+        }
+        if ($coupon['expiresAt'] !== null && $coupon['expiresAt'] !== '' && $now > $coupon['expiresAt']) {
+            return CouponResult::fail(CouponResult::expired, $coupon);
+        }
+        if ($coupon['maxRedemptions'] !== null && (int) $coupon['redeemedCount'] >= (int) $coupon['maxRedemptions']) {
+            return CouponResult::fail(CouponResult::exhausted, $coupon);
+        }
+        if ($subtotalCents < (int) $coupon['minSubtotalCents']) {
+            return CouponResult::fail(CouponResult::belowMinimum, $coupon);
+        }
+
+        return CouponResult::ok($coupon, $this->discountFor($coupon, $subtotalCents));
+    }
+
+    public function discountFor(array $coupon, int $subtotalCents): int
+    {
+        $discount = $coupon['type'] === 'percent'
+            ? (int) floor($subtotalCents * (int) $coupon['value'] / 100)
+            : (int) $coupon['value'];
+
+        return max(0, min($discount, $subtotalCents));
+    }
+
+    public function redeem(int $couponId): void
+    {
+        $this->coupons->recordRedemption($couponId);
+    }
+}