fix: account for discounts applied by bpn api in validation request

src/BusProNet/Model/BookingResponse.php

@@ -102,4 +102,45 @@ class BookingResponse
             2
         );
     }
+
+    /**
+     * Gets API-applied discounts that cannot be predicted by the local price calculator.
+     *
+     * The BusProNet API may apply automatic discounts based on business rules that
+     * are not known to the local application, such as:
+     * - ERM/GRU: Gruppenrabatt (group discount for large bookings)
+     * - Other ERM subtypes: Various automatic discounts
+     *
+     * These discounts appear as negative price items and must be accounted for when
+     * comparing the API total price against the locally calculated price.
+     *
+     * Note: Voucher discounts (AKTION, KULANZGUTSCHEIN) are handled separately via
+     * getVoucherDiscountFromPrices() as they are user-initiated, not automatic.
+     *
+     * @return array<PriceItem> Price items representing API-applied automatic discounts
+     */
+    public function getApiAppliedDiscounts(): array
+    {
+        return array_filter(
+            $this->priceItems,
+            fn (PriceItem $item) => $item->totalPrice < 0
+                && false === \in_array($item->type, ['AKTION', 'KULANZGUTSCHEIN'], true)
+        );
+    }
+
+    /**
+     * Gets total discount from API-applied automatic discounts.
+     *
+     * Returns the absolute sum of negative price items that represent automatic
+     * discounts applied by the API (excluding voucher discounts which are handled separately).
+     */
+    public function getApiAppliedDiscountTotal(): float
+    {
+        $discount = 0.0;
+        foreach ($this->getApiAppliedDiscounts() as $item) {
+            $discount += abs($item->totalPrice);
+        }
+
+        return round($discount, 2);
+    }
 }

src/Controller/Booking/Create/Step3Controller.php

@@ -115,12 +115,15 @@ class Step3Controller extends AbstractController
                 }
 
                 // Validate price match (rounded to cent precision to avoid floating-point errors)
-                // API gesamtpreis includes promotional/goodwill voucher discounts (negative price items),
+                // API gesamtpreis includes:
-                // but NOT purchase vouchers (those reduce restzahlung, not gesamtpreis)
+                // - Promotional/goodwill voucher discounts (negative price items with art=AKTION/KULANZGUTSCHEIN)
+                // - API-applied automatic discounts (e.g., Gruppenrabatt with art=ERM)
+                // - NOT purchase vouchers (those reduce restzahlung, not gesamtpreis)
                 $apiTotal = round($inquiryResponse->totalPrice ?? 0.0, 2);
                 $calculatedSubtotal = round($this->priceCalculator->calculateGrandTotal($bookingCreateDto), 2);
                 $promoGoodwillDiscount = round($inquiryResponse->getVoucherDiscountFromPrices(), 2);
-                $expectedTotal = round($calculatedSubtotal - $promoGoodwillDiscount, 2);
+                $apiAppliedDiscount = round($inquiryResponse->getApiAppliedDiscountTotal(), 2);
+                $expectedTotal = round($calculatedSubtotal - $promoGoodwillDiscount - $apiAppliedDiscount, 2);
 
                 if ((int) round($apiTotal * 100) !== (int) round($expectedTotal * 100)) {
                     return $this->handleApiError(
@@ -129,6 +132,7 @@ class Step3Controller extends AbstractController
                             'apiTotal' => $apiTotal,
                             'calculatedSubtotal' => $calculatedSubtotal,
                             'promoGoodwillDiscount' => $promoGoodwillDiscount,
+                            'apiAppliedDiscount' => $apiAppliedDiscount,
                             'expectedTotal' => $expectedTotal,
                             'difference' => abs($apiTotal - $expectedTotal),
                         ],

tests/BusProNet/XmlParser/BookingResponseParserTest.php

@@ -209,4 +209,107 @@ class BookingResponseParserTest extends TestCase
         $this->assertEquals(125.0, $response->paymentTerms->getPurchaseVoucherDiscount()); // 50 + 75
         $this->assertEquals(125.0, $response->getTotalVoucherDiscount());
     }
+
+    public function testParseBookingResponseWithGruppenrabatt(): void
+    {
+        $xmlContent = '<?xml version="1.0" encoding="utf-8"?>
+<ergebnis>
+    <satz typ="BUCHUNG" />
+    <buchung>möglich</buchung>
+    <vorgang>321530</vorgang>
+    <preise>
+        <preis position="1" art="UNT" unterart="ZIM" bezeichnung="Doppelzimmer Dusche/WC" terminvon="27.03.2026" terminbis="29.03.2026" anzahl="6" zuordnung="1,2,3,4,5,6,7,8,9,10,11,12" preis="229,00" gesamtpreis="2748,00" />
+        <preis position="2" art="UNT" unterart="ZIM" bezeichnung="3er Zimmer Dusche/WC" terminvon="27.03.2026" terminbis="29.03.2026" anzahl="2" zuordnung="13,14,15,16,17,18" preis="219,00" gesamtpreis="1314,00" />
+        <preis position="3" art="ERM" unterart="GRU" bezeichnung="Gruppenrabatt" anzahl="1" preis="-90,00" gesamtpreis="-90,00" />
+    </preise>
+    <gesamtpreis>3972,00</gesamtpreis>
+    <zahlungsbedingungen>
+        <restzahlung betrag="3972,00" termin="02.12.2029"></restzahlung>
+    </zahlungsbedingungen>
+</ergebnis>';
+
+        $crawler = new Crawler($xmlContent);
+        $response = $this->parser->parse($crawler->filter('ergebnis'));
+
+        $this->assertTrue($response->isInquiryValid());
+        $this->assertEquals(3972.0, $response->totalPrice);
+
+        // Verify Gruppenrabatt is NOT counted as voucher discount
+        $this->assertCount(0, $response->getVoucherDiscountsFromPrices());
+        $this->assertEquals(0.0, $response->getVoucherDiscountFromPrices());
+
+        // Verify Gruppenrabatt IS counted as API-applied discount
+        $apiAppliedDiscounts = $response->getApiAppliedDiscounts();
+        $this->assertCount(1, $apiAppliedDiscounts);
+
+        $gruppenrabatt = array_values($apiAppliedDiscounts)[0];
+        $this->assertEquals('ERM', $gruppenrabatt->type);
+        $this->assertEquals('GRU', $gruppenrabatt->subType);
+        $this->assertEquals('Gruppenrabatt', $gruppenrabatt->label);
+        $this->assertEquals(-90.0, $gruppenrabatt->totalPrice);
+
+        $this->assertEquals(90.0, $response->getApiAppliedDiscountTotal());
+    }
+
+    public function testParseBookingResponseWithGruppenrabattAndVouchers(): void
+    {
+        $xmlContent = '<?xml version="1.0" encoding="utf-8"?>
+<ergebnis>
+    <satz typ="BUCHUNG" />
+    <buchung>möglich</buchung>
+    <vorgang>321530</vorgang>
+    <preise>
+        <preis position="1" art="UNT" unterart="ZIM" bezeichnung="Doppelzimmer" preis="500,00" gesamtpreis="500,00" />
+        <preis position="2" art="AKTION" unterart="" bezeichnung="PROMO20" anzahl="1" zuordnung="1" preis="-20,00" gesamtpreis="-20,00" />
+        <preis position="3" art="ERM" unterart="GRU" bezeichnung="Gruppenrabatt" anzahl="1" preis="-50,00" gesamtpreis="-50,00" />
+    </preise>
+    <gesamtpreis>430,00</gesamtpreis>
+    <zahlungsbedingungen>
+        <restzahlung betrag="430,00" termin="02.12.2029"></restzahlung>
+    </zahlungsbedingungen>
+</ergebnis>';
+
+        $crawler = new Crawler($xmlContent);
+        $response = $this->parser->parse($crawler->filter('ergebnis'));
+
+        // Voucher discount should only include AKTION
+        $this->assertEquals(20.0, $response->getVoucherDiscountFromPrices());
+
+        // API-applied discount should only include ERM (Gruppenrabatt)
+        $this->assertEquals(50.0, $response->getApiAppliedDiscountTotal());
+
+        // Verify they are separate and don't overlap
+        $voucherDiscounts = $response->getVoucherDiscountsFromPrices();
+        $apiDiscounts = $response->getApiAppliedDiscounts();
+
+        $this->assertCount(1, $voucherDiscounts);
+        $this->assertCount(1, $apiDiscounts);
+
+        $this->assertEquals('AKTION', array_values($voucherDiscounts)[0]->type);
+        $this->assertEquals('ERM', array_values($apiDiscounts)[0]->type);
+    }
+
+    public function testParseBookingResponseWithNoApiAppliedDiscounts(): void
+    {
+        $xmlContent = '<?xml version="1.0" encoding="utf-8"?>
+<ergebnis>
+    <satz typ="BUCHUNG" />
+    <buchung>möglich</buchung>
+    <vorgang>321530</vorgang>
+    <preise>
+        <preis position="1" art="UNT" unterart="ZIM" bezeichnung="Bett im Mehrbettzimmer" preis="679,00" gesamtpreis="679,00" />
+    </preise>
+    <gesamtpreis>679,00</gesamtpreis>
+    <zahlungsbedingungen>
+        <restzahlung betrag="679,00" termin="02.12.2029"></restzahlung>
+    </zahlungsbedingungen>
+</ergebnis>';
+
+        $crawler = new Crawler($xmlContent);
+        $response = $this->parser->parse($crawler->filter('ergebnis'));
+
+        // Verify no API-applied discounts
+        $this->assertCount(0, $response->getApiAppliedDiscounts());
+        $this->assertEquals(0.0, $response->getApiAppliedDiscountTotal());
+    }
 }