add refund logic and fix books inventory logic

tests/app/Services/FeeCalculationServiceTest.php

@@ -5,8 +5,51 @@ namespace Tests\App\Services;
 use App\Services\FeeCalculationService;
 use CodeIgniter\Test\CIUnitTestCase;
 
+class FeeCalculationServiceRefundAdapterHarness extends FeeCalculationService
+{
+    public array $previewedEnrollmentIds = [];
+
+    public function __construct(private array $latestByEnrollment, private array $previewByEnrollment)
+    {
+    }
+
+    protected function latestWithdrawalCalculation(int $enrollmentId): ?array
+    {
+        return $this->latestByEnrollment[$enrollmentId] ?? null;
+    }
+
+    protected function previewWithdrawalCalculation(int $enrollmentId): array
+    {
+        $this->previewedEnrollmentIds[] = $enrollmentId;
+        return $this->previewByEnrollment[$enrollmentId] ?? ['new_refund_request_cents' => 0];
+    }
+}
+
 class FeeCalculationServiceTest extends CIUnitTestCase
 {
+    public function testRefundAdapterUsesWithdrawalFinancialPreviewAmounts(): void
+    {
+        $service = new FeeCalculationServiceRefundAdapterHarness(
+            latestByEnrollment: [
+                10 => ['status' => 'preview', 'new_refund_request_cents' => 12345],
+                11 => ['status' => 'superseded', 'new_refund_request_cents' => 99999],
+            ],
+            previewByEnrollment: [
+                11 => ['status' => 'preview', 'new_refund_request_cents' => 500],
+            ]
+        );
+
+        $refund = $service->calculateRefund([
+            ['id' => 10, 'parent_id' => 8, 'enrollment_status' => 'withdraw under review'],
+            ['id' => 11, 'parent_id' => 8, 'enrollment_status' => 'refund pending'],
+            ['id' => 12, 'parent_id' => 8, 'enrollment_status' => 'enrolled'],
+            ['id' => 13, 'parent_id' => 9, 'enrollment_status' => 'refund pending'],
+        ], 8);
+
+        $this->assertSame(128.45, $refund);
+        $this->assertSame([11], $service->previewedEnrollmentIds);
+    }
+
     public function testRefundReversesLatestTuitionTierFirst(): void
     {
         $fees = $this->refundFeeStack(3, 2, 380.0, 280.0);