feat(scripting_api)!: clean up Subscription interface

lib/src/scripting_api/subscription.dart

@@ -10,7 +10,7 @@
 
 import '../definitions/form.dart';
 import '../definitions/interaction_affordances/interaction_affordance.dart';
-import 'consumed_thing.dart';
+import 'interaction_options.dart';
 
 /// Indicates the type of the subscription.
 enum SubscriptionType {
@@ -23,11 +23,71 @@ enum SubscriptionType {
 
 /// Represents a subscription to Property change and Event interactions.
 abstract class Subscription {
-  /// Indicates what WoT Interaction this [Subscription] refers to.
-  SubscriptionType? type;
+  /// Denotes whether the subsciption is active, i.e. it is not stopped because
+  /// of an error or because of invocation of the [stop] method.
+  bool get active;
 
-  /// The Property or Event name.
-  String? name;
+  /// Stops delivering notifications for the subscription.
+  /// It takes an optional parameter [options] and returns a [Future].
+  Future<void> stop([InteractionOptions? options]);
+}
+
+/// Finds a matching unsubscribe [Form] for a subscription [form].
+///
+/// Uses either a dedicated [formIndex] or determines the [Form] using
+/// the [interaction] Affordance and the [type] of subscription it belongs to.
+// TODO(JKRhb): Using an index does not seem the best idea to me.
+Form findUnsubscribeForm(InteractionAffordance interaction,
+    SubscriptionType type, Form form, int? formIndex) {
+  if (formIndex != null) {
+    interaction.forms[formIndex];
+  }
+
+  final operationType = _determineOpType(type);
+  final formOperations = form.op;
+
+  // The default op value also contains the unsubscribe/unobserve operation.
+  if (formOperations == null || formOperations.contains(operationType)) {
+    return form;
+  }
+
+  final unsubscribeForm = _findFormByScoring(interaction, form, operationType);
+
+  if (unsubscribeForm == null) {
+    // TODO(JKRhb): Add appropriate Exception type.
+    throw Exception("Could not find matching form for unsubscribe");
+  }
+
+  return unsubscribeForm;
+}
+
+String _determineOpType(SubscriptionType? subscriptionType) {
+  switch (subscriptionType) {
+    case SubscriptionType.event:
+      return "unsubscribeevent";
+    case SubscriptionType.property:
+      return "unobserveproperty";
+    default:
+      throw Exception();
+  }
+}
+
+Form? _findFormByScoring(
+    InteractionAffordance interaction, Form form, String operationType) {
+  int maxScore = 0;
+  Form? foundForm;
+
+  for (Form currentForm in interaction.augmentedForms) {
+    int score;
+    if (form.op!.contains(operationType)) {
+      score = 1;
+    } else {
+      continue;
+    }
+
+    if (Uri.parse(form.href).origin == Uri.parse(currentForm.href).origin) {
+      score++;
+    }
 
   /// The Thing Description fragment that describes the WoT [interaction].
   InteractionAffordance? interaction;