Show appropriate error dialog for free users when sharing is disabled

lib/services/collections_service.dart

@@ -145,21 +145,27 @@ class CollectionsService {
     });
   }
 
-  Future<void> share(int collectionID, String email, String publicKey) {
+  Future<void> share(int collectionID, String email, String publicKey) async {
     final encryptedKey = CryptoUtil.sealSync(
         getCollectionKey(collectionID), Sodium.base642bin(publicKey));
-    return _dio
-        .post(
-          Configuration.instance.getHttpEndpoint() + "/collections/share",
-          data: {
-            "collectionID": collectionID,
-            "email": email,
-            "encryptedKey": Sodium.bin2base64(encryptedKey),
-          },
-          options: Options(
-              headers: {"X-Auth-Token": Configuration.instance.getToken()}),
-        )
-        .then((value) => SyncService.instance.syncWithRemote(silently: true));
+    try {
+      await _dio.post(
+        Configuration.instance.getHttpEndpoint() + "/collections/share",
+        data: {
+          "collectionID": collectionID,
+          "email": email,
+          "encryptedKey": Sodium.bin2base64(encryptedKey),
+        },
+        options: Options(
+            headers: {"X-Auth-Token": Configuration.instance.getToken()}),
+      );
+    } on DioError catch (e) {
+      if (e.response.statusCode == 402) {
+        throw SharingNotPermittedForFreeAccountsError();
+      }
+      throw e;
+    }
+    SyncService.instance.syncWithRemote(silently: true);
   }
 
   Future<void> unshare(int collectionID, String email) {
@@ -434,3 +440,5 @@ class AddFilesRequest {
   @override
   int get hashCode => collectionID.hashCode ^ files.hashCode;
 }
+
+class SharingNotPermittedForFreeAccountsError extends Error {}

lib/ui/share_collection_widget.dart

@@ -13,6 +13,7 @@ import 'package:photos/services/sync_service.dart';
 import 'package:photos/services/user_service.dart';
 import 'package:photos/ui/common_elements.dart';
 import 'package:photos/ui/loading_widget.dart';
+import 'package:photos/ui/subscription_page.dart';
 import 'package:photos/utils/dialog_util.dart';
 import 'package:photos/utils/email_util.dart';
 import 'package:photos/utils/share_util.dart';
@@ -212,7 +213,42 @@ class _SharingDialogState extends State<SharingDialog> {
         });
       } catch (e) {
         await dialog.hide();
-        showGenericErrorDialog(context);
+        if (e is SharingNotPermittedForFreeAccountsError) {
+          AlertDialog alert = AlertDialog(
+            title: Text("sorry"),
+            content: Text(
+                "sharing is not permitted for free accounts, please subscribe"),
+            actions: [
+              FlatButton(
+                child: Text("subscribe"),
+                onPressed: () {
+                  Navigator.of(context).pushReplacement(
+                    MaterialPageRoute(
+                      builder: (BuildContext context) {
+                        return SubscriptionPage();
+                      },
+                    ),
+                  );
+                },
+              ),
+              FlatButton(
+                child: Text("ok"),
+                onPressed: () {
+                  Navigator.of(context).pop();
+                },
+              ),
+            ],
+          );
+
+          showDialog(
+            context: context,
+            builder: (BuildContext context) {
+              return alert;
+            },
+          );
+        } else {
+          showGenericErrorDialog(context);
+        }
       }
     }
   }