Improve expanding responses

lib/messages.dart

@@ -1,6 +1,8 @@
 import 'package:json_annotation/json_annotation.dart';
 import 'package:stripe/src/messages/converters.dart';
 import 'package:stripe/src/messages/enums.dart';
+import 'package:stripe/src/resources/payment_intent.dart';
+import 'package:stripe/src/utils/expandable.dart';
 
 export 'package:stripe/src/messages/enums.dart';
 

lib/src/messages/converters.dart

@@ -1,4 +1,5 @@
 import 'package:json_annotation/json_annotation.dart';
+import 'package:stripe/src/utils/expandable.dart';
 
 /// Converts a [DateTime] to a timestamp int and vice versa.
 class TimestampConverter implements JsonConverter<DateTime, int> {
@@ -11,3 +12,61 @@ class TimestampConverter implements JsonConverter<DateTime, int> {
   @override
   int toJson(DateTime type) => type.millisecondsSinceEpoch ~/ 1000;
 }
+
+class ExpandableJsonConverter<T>
+    implements JsonConverter<Expandable<T>, Object> {
+  final T Function(Map<String, dynamic> json) expandedFromJson;
+
+  const ExpandableJsonConverter(this.expandedFromJson);
+
+  @override
+  Expandable<T> fromJson(Object json) {
+    if (json is String) {
+      return Expandable(id: json);
+    }
+
+    if (json is Map<String, dynamic>) {
+      return Expandable(
+        id: json['id'] as String,
+        expanded: expandedFromJson(json),
+      );
+    }
+
+    throw ArgumentError('expected an String or a Map<String, dynamic>');
+  }
+
+  @override
+  Object toJson(Expandable<T> object) {
+    return object.id;
+  }
+}
+
+class ExpandableListJsonConverter<T>
+    implements JsonConverter<ExpandableList<T>, List<dynamic>> {
+  final T Function(Map<String, dynamic> json) expandedFromJson;
+
+  const ExpandableListJsonConverter(this.expandedFromJson);
+
+  @override
+  ExpandableList<T> fromJson(List<dynamic> json) {
+    if (json.isEmpty) {
+      return ExpandableList(ids: [], expanded: []);
+    }
+
+    if (json.first is String) {
+      return ExpandableList(ids: json.cast<String>());
+    }
+
+    // Assuming that json is List<Map<String, dynamic>>.
+    final jsonList = json.cast<Map<String, dynamic>>();
+    final idsList = jsonList.map((element) => element['id'] as String).toList();
+    final parsedList = jsonList.map(expandedFromJson).toList();
+
+    return ExpandableList(ids: idsList, expanded: parsedList);
+  }
+
+  @override
+  List<dynamic> toJson(ExpandableList<T> object) {
+    return object.ids;
+  }
+}

lib/src/messages/discount.dart

@@ -71,3 +71,13 @@ class Discount extends Message {
   @override
   Map<String, dynamic> toJson() => _$DiscountToJson(this);
 }
+
+class ExpandableDiscountJsonConverter
+    extends ExpandableJsonConverter<Discount> {
+  const ExpandableDiscountJsonConverter() : super(Discount.fromJson);
+}
+
+class ExpandableDiscountListJsonConverter
+    extends ExpandableListJsonConverter<Discount> {
+  const ExpandableDiscountListJsonConverter() : super(Discount.fromJson);
+}

lib/src/messages/enums.dart

@@ -1,8 +1,6 @@
-export 'enums/expandable_fields/invoice_expandable_field.dart';
-export 'enums/expandable_fields/subscription_expandable_field.dart';
+export 'enums/pause_collection_behavior.dart';
 export 'enums/payment_behavior.dart';
 export 'enums/proration_behavior.dart';
-export 'enums/stripe_api_error_type.dart';
-export 'enums/pause_collection_behavior.dart';
-export 'enums/source_type.dart';
 export 'enums/source_status.dart';
+export 'enums/source_type.dart';
+export 'enums/stripe_api_error_type.dart';

lib/src/messages/expandable_objects/customer_expandable_object.dart

@@ -0,0 +1,4 @@
+import 'package:stripe/messages.dart';
+import 'package:stripe/src/messages/expandable_objects/expandable_object.dart';
+
+typedef CustomerExpandableObject = SimpleExpandableObject<Customer>;

lib/src/messages/expandable_objects/discount_expandable_object.dart

@@ -0,0 +1,4 @@
+import 'package:stripe/messages.dart';
+import 'package:stripe/src/messages/expandable_objects/expandable_object.dart';
+
+typedef DiscountExpandableObject = SimpleExpandableObject<Discount>;

lib/src/messages/expandable_objects/expandable_object.dart

@@ -0,0 +1,60 @@
+import 'package:stripe/src/utils/map_extension.dart';
+
+/// A class that helps generating queries for expanding API responses.
+/// [expandableFields] must be implemented.
+///
+/// Examples of queries that can be generated by [expandQuery] method:
+/// ```
+/// ["discounts"]
+/// ["latest_invoice.payment_intent", "latest_invoice.payment_intent"]
+/// ```
+///
+/// /// Expanding Stripe API responses: https://docs.stripe.com/expand
+abstract class ExpandableObject<T> {
+  Map<String, ExpandableObject?> get expandableFields;
+
+  Map<String, ExpandableObject> get expand =>
+      expandableFields.whereValueNotNull();
+
+  const ExpandableObject();
+
+  List<String>? expandQuery() {
+    final query = _generateExpandQuery().toList();
+
+    if (query.isEmpty) return null;
+
+    return query.toList();
+  }
+
+  Iterable<String> _generateExpandQuery() sync* {
+    for (final fieldEntry in expand.entries) {
+      final fieldName = fieldEntry.key;
+      final fieldExpandObject = fieldEntry.value;
+      yield* _generateExpandQueryForField(fieldName, fieldExpandObject);
+    }
+  }
+
+  Iterable<String> _generateExpandQueryForField(
+    String name,
+    ExpandableObject<dynamic> object,
+  ) sync* {
+    final innerExpandFields = object.expandQuery();
+
+    if (innerExpandFields == null || innerExpandFields.isEmpty) {
+      yield name;
+    } else {
+      for (final field in innerExpandFields) {
+        yield [name, field].join('.');
+      }
+    }
+  }
+}
+
+/// An implementation of ExpandableObject<T> for objects that don't have any
+/// nested expandable fields.
+class SimpleExpandableObject<T> extends ExpandableObject<T> {
+  @override
+  Map<String, ExpandableObject?> get expandableFields => const {};
+
+  const SimpleExpandableObject();
+}

lib/src/messages/expandable_objects/invoice_expandable_object.dart

@@ -0,0 +1,20 @@
+import 'package:stripe/messages.dart';
+import 'package:stripe/src/messages/expandable_objects/discount_expandable_object.dart';
+import 'package:stripe/src/messages/expandable_objects/expandable_object.dart';
+import 'package:stripe/src/messages/expandable_objects/payment_intent_expandable_object.dart';
+
+class InvoiceExpandableObject extends ExpandableObject<Invoice> {
+  final PaymentIntentExpandableObject? paymentIntent;
+  final DiscountExpandableObject? discounts;
+
+  @override
+  Map<String, ExpandableObject?> get expandableFields => {
+        'payment_intent': paymentIntent,
+        'discounts': discounts,
+      };
+
+  const InvoiceExpandableObject({
+    this.paymentIntent,
+    this.discounts,
+  });
+}

lib/src/messages/expandable_objects/payment_intent_expandable_object.dart

@@ -0,0 +1,4 @@
+import 'package:stripe/messages.dart';
+import 'package:stripe/src/messages/expandable_objects/expandable_object.dart';
+
+typedef PaymentIntentExpandableObject = SimpleExpandableObject<Discount>;