fix: parse subscriptionOffers for iOS subscription products

- Add _parseSubscriptionOffersIOS helper function
- Parse subscriptionOffers from native iOS data in ProductSubscriptionIOS
- Add unit test for subscriptionOffers parsing

Fixes #616

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: hyochan

lib/helpers.dart

@@ -121,6 +121,9 @@ gentype.ProductCommon parseProductFromNative(
         subscriptionInfoIOS: _parseSubscriptionInfoIOS(
           json['subscriptionInfoIOS'] ?? json['subscription'],
         ),
+        subscriptionOffers: _parseSubscriptionOffersIOS(
+          json['subscriptionOffers'],
+        ),
         subscriptionPeriodNumberIOS:
             json['subscriptionPeriodNumberIOS']?.toString(),
         subscriptionPeriodUnitIOS: _parseSubscriptionPeriod(
@@ -635,6 +638,103 @@ gentype.SubscriptionInfoIOS? _parseSubscriptionInfoIOS(dynamic value) {
   return null;
 }
 
+/// Parse standardized SubscriptionOffer list from iOS native data.
+List<gentype.SubscriptionOffer>? _parseSubscriptionOffersIOS(dynamic json) {
+  if (json == null) return null;
+  if (json is! List) return null;
+
+  final offers = <gentype.SubscriptionOffer>[];
+  for (final item in json) {
+    final map = normalizeDynamicMap(item);
+    if (map == null) continue;
+
+    // Parse payment mode
+    gentype.PaymentMode? paymentMode;
+    final paymentModeRaw = map['paymentMode']?.toString().toUpperCase();
+    if (paymentModeRaw != null) {
+      try {
+        paymentMode = gentype.PaymentMode.fromJson(paymentModeRaw);
+      } catch (_) {
+        // Fallback mapping
+        switch (paymentModeRaw) {
+          case 'FREE_TRIAL':
+          case 'FREETRIAL':
+            paymentMode = gentype.PaymentMode.FreeTrial;
+            break;
+          case 'PAY_UP_FRONT':
+          case 'PAYUPFRONT':
+            paymentMode = gentype.PaymentMode.PayUpFront;
+            break;
+          case 'PAY_AS_YOU_GO':
+          case 'PAYASYOUGO':
+            paymentMode = gentype.PaymentMode.PayAsYouGo;
+            break;
+        }
+      }
+    }
+
+    // Parse offer type
+    gentype.DiscountOfferType type = gentype.DiscountOfferType.Introductory;
+    final typeRaw = map['type']?.toString().toUpperCase();
+    if (typeRaw != null) {
+      try {
+        type = gentype.DiscountOfferType.fromJson(typeRaw);
+      } catch (_) {
+        switch (typeRaw) {
+          case 'PROMOTIONAL':
+          case 'WIN_BACK':
+          case 'WINBACK':
+          case 'CODE':
+            type = gentype.DiscountOfferType.Promotional;
+            break;
+          case 'ONE_TIME':
+          case 'ONETIME':
+            type = gentype.DiscountOfferType.OneTime;
+            break;
+        }
+      }
+    }
+
+    // Parse period
+    gentype.SubscriptionPeriod? period;
+    final periodMap = normalizeDynamicMap(map['period']);
+    if (periodMap != null) {
+      final unitRaw = periodMap['unit']?.toString().toUpperCase();
+      final value = (periodMap['value'] as num?)?.toInt() ?? 1;
+      gentype.SubscriptionPeriodUnit? unit;
+      if (unitRaw != null) {
+        try {
+          unit = gentype.SubscriptionPeriodUnit.fromJson(unitRaw);
+        } catch (_) {
+          // ignore
+        }
+      }
+      if (unit != null) {
+        period = gentype.SubscriptionPeriod(unit: unit, value: value);
+      }
+    }
+
+    offers.add(gentype.SubscriptionOffer(
+      id: map['id']?.toString() ?? '',
+      displayPrice: map['displayPrice']?.toString() ?? '',
+      price: (map['price'] as num?)?.toDouble() ?? 0,
+      currency: map['currency']?.toString(),
+      type: type,
+      paymentMode: paymentMode,
+      period: period,
+      periodCount: (map['periodCount'] as num?)?.toInt(),
+      keyIdentifierIOS: map['keyIdentifierIOS']?.toString(),
+      nonceIOS: map['nonceIOS']?.toString(),
+      signatureIOS: map['signatureIOS']?.toString(),
+      timestampIOS: (map['timestampIOS'] as num?)?.toDouble(),
+      numberOfPeriodsIOS: (map['numberOfPeriodsIOS'] as num?)?.toInt(),
+      localizedPriceIOS: map['localizedPriceIOS']?.toString(),
+    ));
+  }
+
+  return offers.isEmpty ? null : offers;
+}
+
 /// Parse standardized SubscriptionOffer list from subscription offer details.
 /// Converts legacy subscriptionOfferDetailsAndroid to cross-platform SubscriptionOffer.
 List<gentype.SubscriptionOffer> _parseSubscriptionOffers(

test/helpers_unit_test.dart

@@ -43,6 +43,74 @@ void main() {
       expect(subscription.type, types.ProductType.Subs);
     });
 
+    test(
+      'parseProductFromNative parses subscriptionOffers for iOS subscription',
+      () {
+        final product = parseProductFromNative(
+          <String, dynamic>{
+            'platform': 'ios',
+            'id': 'premium_yearly',
+            'title': 'Premium Yearly',
+            'description': 'Yearly plan',
+            'currency': 'USD',
+            'displayPrice': '\$49.99',
+            'price': 49.99,
+            'isFamilyShareableIOS': true,
+            'jsonRepresentationIOS': '{}',
+            'typeIOS': 'AUTO_RENEWABLE_SUBSCRIPTION',
+            'subscriptionOffers': <Map<String, dynamic>>[
+              <String, dynamic>{
+                'id': 'intro_offer',
+                'displayPrice': 'Free',
+                'price': 0.0,
+                'type': 'INTRODUCTORY',
+                'paymentMode': 'FREE_TRIAL',
+                'periodCount': 1,
+                'period': <String, dynamic>{
+                  'unit': 'WEEK',
+                  'value': 1,
+                },
+              },
+              <String, dynamic>{
+                'id': 'promo_offer',
+                'displayPrice': '\$29.99',
+                'price': 29.99,
+                'type': 'PROMOTIONAL',
+                'paymentMode': 'PAY_AS_YOU_GO',
+                'periodCount': 3,
+                'numberOfPeriodsIOS': 3,
+                'localizedPriceIOS': '\$29.99/month',
+              },
+            ],
+          },
+          'subs',
+          fallbackIsIOS: true,
+        );
+
+        expect(product, isA<types.ProductSubscriptionIOS>());
+        final subscription = product as types.ProductSubscriptionIOS;
+        expect(subscription.subscriptionOffers, isNotNull);
+        expect(subscription.subscriptionOffers, hasLength(2));
+
+        final introOffer = subscription.subscriptionOffers!.first;
+        expect(introOffer.id, 'intro_offer');
+        expect(introOffer.type, types.DiscountOfferType.Introductory);
+        expect(introOffer.paymentMode, types.PaymentMode.FreeTrial);
+        expect(introOffer.price, 0.0);
+        expect(introOffer.period, isNotNull);
+        expect(introOffer.period!.unit, types.SubscriptionPeriodUnit.Week);
+        expect(introOffer.period!.value, 1);
+
+        final promoOffer = subscription.subscriptionOffers![1];
+        expect(promoOffer.id, 'promo_offer');
+        expect(promoOffer.type, types.DiscountOfferType.Promotional);
+        expect(promoOffer.paymentMode, types.PaymentMode.PayAsYouGo);
+        expect(promoOffer.price, 29.99);
+        expect(promoOffer.numberOfPeriodsIOS, 3);
+        expect(promoOffer.localizedPriceIOS, '\$29.99/month');
+      },
+    );
+
     test(
       'parseProductFromNative creates Android in-app product with string offers',
       () {