Improve Google Play subscription offer handling

Platforms/Android/AndroidPlayBillingService.cs

@@ -9,6 +9,7 @@ public sealed class AndroidPlayBillingService : Java.Lang.Object, IPlayBillingSe
     private readonly SemaphoreSlim _connectionLock = new(1, 1);
     private readonly BillingClient _client;
     private TaskCompletionSource<PlayBillingResult>? _purchaseCompletion;
+    private string? _lastCatalogFailure;
 
     public AndroidPlayBillingService()
     {
@@ -31,7 +32,12 @@ public sealed class AndroidPlayBillingService : Java.Lang.Object, IPlayBillingSe
         {
             var details = await GetProductDetailsAsync(cancellationToken);
             return details?.GetSubscriptionOfferDetails()?
-                .Where(item => string.IsNullOrEmpty(item.OfferId))
+                .Where(item => !string.IsNullOrWhiteSpace(item.BasePlanId)
+                    && !string.IsNullOrWhiteSpace(item.OfferToken))
+                .GroupBy(item => item.BasePlanId, StringComparer.Ordinal)
+                .Select(group => group
+                    .OrderBy(item => string.IsNullOrEmpty(item.OfferId) ? 0 : 1)
+                    .First())
                 .Select(item =>
                 {
                     var phase = item.PricingPhases.PricingPhaseList.LastOrDefault();
@@ -99,13 +105,25 @@ public sealed class AndroidPlayBillingService : Java.Lang.Object, IPlayBillingSe
 
             var details = await GetProductDetailsAsync(cancellationToken);
             var offer = details?.GetSubscriptionOfferDetails()?
-                .FirstOrDefault(item => item.BasePlanId == basePlanId
-                    && string.IsNullOrEmpty(item.OfferId)
-                    && !string.IsNullOrWhiteSpace(item.OfferToken));
-            if (details is null || offer is null)
+                .Where(item => item.BasePlanId == basePlanId
+                    && !string.IsNullOrWhiteSpace(item.OfferToken))
+                .OrderBy(item => string.IsNullOrEmpty(item.OfferId) ? 0 : 1)
+                .FirstOrDefault();
+            if (details is null)
             {
-                return PlayBillingResult.Failed(
-                    $"Piano {basePlanId} non disponibile su Google Play. Verifica che l'abbonamento lme_pro e il piano siano attivi per il tuo Paese.");
+                return PlayBillingResult.Failed(_lastCatalogFailure
+                    ?? "Google Play non ha restituito l'abbonamento lme_pro.");
+            }
+
+            if (offer is null)
+            {
+                var availablePlans = string.Join(", ", details.GetSubscriptionOfferDetails()?
+                    .Select(item => item.BasePlanId)
+                    .Where(item => !string.IsNullOrWhiteSpace(item))
+                    .Distinct(StringComparer.Ordinal) ?? []);
+                return PlayBillingResult.Failed(string.IsNullOrWhiteSpace(availablePlans)
+                    ? $"Google Play ha restituito lme_pro senza offerte acquistabili per il piano {basePlanId}."
+                    : $"Piano {basePlanId} non restituito da Google Play. Piani ricevuti: {availablePlans}.");
             }
 
             var productParams = BillingFlowParams.ProductDetailsParams.NewBuilder()
@@ -191,7 +209,18 @@ public sealed class AndroidPlayBillingService : Java.Lang.Object, IPlayBillingSe
             throw new InvalidOperationException(ToMessage(result.Result));
         }
 
-        return result.ProductDetailsList?.FirstOrDefault();
+        var details = result.ProductDetailsList?.FirstOrDefault();
+        if (details is not null)
+        {
+            _lastCatalogFailure = null;
+            return details;
+        }
+
+        var unfetched = result.UnfetchedProductList?.FirstOrDefault();
+        _lastCatalogFailure = unfetched is null
+            ? "Google Play ha restituito un catalogo vuoto per lme_pro. Verifica account Play Store, adesione al test e origine dell'installazione."
+            : $"Google Play non ha caricato lme_pro (codice catalogo {unfetched.StatusCodeValue}).";
+        return null;
     }
 
     private async Task EnsureConnectedAsync(CancellationToken cancellationToken)