diff --git a/src/Discount/Service/DiscountEngine.php b/src/Discount/Service/DiscountEngine.php
new file mode 100644
index 00000000..dc36af2f
--- /dev/null
+++ b/src/Discount/Service/DiscountEngine.php
@@ -0,0 +1,150 @@
+<?php
+
+namespace App\Discount\Service;
+
+use App\Discount\Entity\DiscountRule;
+use App\Discount\Repository\DiscountRuleRepository;
+use App\Patient\Entity\PatientSession;
+use App\Patient\Entity\SessionService;
+use App\Patient\Repository\PatientSessionRepository;
+use App\UserProfile\Repository\UserProfileRepository;
+
+/**
+ * موتور تخفیف: برای یک پرونده، قوانین قابل‌اعمالِ owner را ارزیابی و مبلغ تخفیف
+ * هرکدام را محاسبه می‌کند. اعمال نهایی در PatientService::applyDiscount انجام می‌شود.
+ */
+class DiscountEngine
+{
+    public function __construct(
+        private readonly DiscountRuleRepository   $ruleRepo,
+        private readonly PatientSessionRepository $sessionRepo,
+        private readonly UserProfileRepository    $profileRepo,
+    ) {}
+
+    /**
+     * @return array<int, array{rule_uuid: string, rule_name: string, type: string, discount_type: string, value: int, discount_rials: int, combinable: bool, priority: int}>
+     * مرتب بر priority نزولی (از repository). فقط قوانینِ برقرار با discount_rials > 0.
+     */
+    public function evaluate(PatientSession $session): array
+    {
+        $record = $session->getRecord();
+        $rules  = $this->ruleRepo->findActiveForOwner($record->getEntityType(), $record->getEntityId());
+
+        $final     = $session->getFinalPriceRials();
+        $remaining = max(0, $final - $session->getPaidTotalRials());
+        $now       = time();
+
+        $out = [];
+        foreach ($rules as $rule) {
+            if (!$this->withinValidity($rule, $now)) {
+                continue;
+            }
+            $base = $this->applicableBase($rule, $session, $final, $now);
+            if ($base === null) {
+                continue;
+            }
+            $rials = min($this->computeRials($rule, $base), $remaining);
+            if ($rials <= 0) {
+                continue;
+            }
+            $out[] = [
+                'rule_uuid'      => $rule->getUuid(),
+                'rule_name'      => $rule->getName(),
+                'type'           => $rule->getType(),
+                'discount_type'  => $rule->getDiscountType(),
+                'value'          => $rule->getValue(),
+                'discount_rials' => $rials,
+                'combinable'     => $rule->isCombinable(),
+                'priority'       => $rule->getPriority(),
+            ];
+        }
+        return $out;
+    }
+
+    private function withinValidity(DiscountRule $rule, int $now): bool
+    {
+        if ($rule->getValidFrom() !== null && $now < $rule->getValidFrom()) {
+            return false;
+        }
+        if ($rule->getValidTo() !== null && $now > $rule->getValidTo()) {
+            return false;
+        }
+        return true;
+    }
+
+    /**
+     * مبنای محاسبه‌ی تخفیف اگر قانون برقرار باشد؛ null یعنی قانون اعمال نمی‌شود.
+     */
+    private function applicableBase(DiscountRule $rule, PatientSession $session, int $final, int $now): ?int
+    {
+        $record = $session->getRecord();
+
+        return match ($rule->getType()) {
+            DiscountRule::TYPE_PATIENT_TAG => $this->hasTag($session, $rule->getTargetTagId()) ? $final : null,
+
+            DiscountRule::TYPE_INVOICE_AMOUNT => ($rule->getMinAmountRials() !== null && $final >= $rule->getMinAmountRials()) ? $final : null,
+
+            DiscountRule::TYPE_SPECIFIC_PATIENT => ($rule->getTargetRecordId() !== null && $record->getId() === $rule->getTargetRecordId()) ? $final : null,
+
+            DiscountRule::TYPE_OCCASION => $this->occasionMatches($rule, $session, $now) ? $final : null,
+
+            DiscountRule::TYPE_SERVICE => $this->serviceBase($session, $rule->getTargetServiceItemId()),
+
+            DiscountRule::TYPE_VISIT_COUNT => ($rule->getMinVisitCount() !== null
+                && $this->sessionRepo->countByRecord($record) >= $rule->getMinVisitCount()) ? $final : null,
+
+            default => null,
+        };
+    }
+
+    private function hasTag(PatientSession $session, ?int $tagId): bool
+    {
+        if ($tagId === null) {
+            return false;
+        }
+        foreach ($session->getRecord()->getTags() as $tag) {
+            if ($tag->getId() === $tagId) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /** مبنای تخفیف سرویس = جمع خطوطِ همان سرویس؛ null اگر سرویس در پرونده نباشد. */
+    private function serviceBase(PatientSession $session, ?int $serviceItemId): ?int
+    {
+        if ($serviceItemId === null) {
+            return null;
+        }
+        $sum = 0;
+        foreach ($session->getServices() as $line) {
+            /** @var SessionService $line */
+            if ($line->getServiceItem()->getId() === $serviceItemId) {
+                $sum += $line->getLineTotalRials();
+            }
+        }
+        return $sum > 0 ? $sum : null;
+    }
+
+    private function occasionMatches(DiscountRule $rule, PatientSession $session, int $now): bool
+    {
+        if ($rule->getOccasionKind() !== DiscountRule::OCCASION_BIRTHDAY) {
+            // مناسبت مبتنی بر بازه‌ی تاریخی؛ withinValidity قبلاً چک شده.
+            return true;
+        }
+        $profile = $this->profileRepo->findByUser($session->getRecord()->getUser());
+        $dob = $profile?->getDateOfBirth();
+        if ($dob === null) {
+            return false;
+        }
+        return date('m-d', $dob) === date('m-d', $now);
+    }
+
+    private function computeRials(DiscountRule $rule, int $base): int
+    {
+        if ($rule->getDiscountType() === DiscountRule::DISCOUNT_PERCENT) {
+            return (int) round($base * min(100, $rule->getValue()) / 100);
+        }
+        return min($rule->getValue(), $base);
+    }
+}