feat: implement exploreDirectory method

lib/src/core/thing_discovery.dart

@@ -375,3 +375,64 @@ extension _FlatStreamExtension<T> on Stream<Stream<T>> {
     }
   }
 }
+
+/// Implemention of the [scripting_api.ThingDiscoveryProcess] interface.
+class ThingDiscoveryProcess extends Stream<ThingDescription>
+    implements scripting_api.ThingDiscoveryProcess {
+  /// Constructs a new [ThingDiscoveryProcess].
+  ///
+  /// Accepts an [Iterable] of [ThingDescription]s, which are filtered by an
+  /// optional [thingFilter].
+  ThingDiscoveryProcess(
+    Stream<ThingDescription> thingDescriptions,
+    this.thingFilter,
+  ) {
+    _streamController.addStream(thingDescriptions);
+  }
+
+  final _streamController = StreamController<ThingDescription>();
+
+  var _done = false;
+
+  @override
+  bool get done => _done;
+
+  Exception? _error;
+
+  @override
+  Exception? get error => _error;
+
+  @override
+  final scripting_api.ThingFilter? thingFilter;
+
+  @override
+  StreamSubscription<ThingDescription> listen(
+    void Function(ThingDescription event)? onData, {
+    Function? onError,
+    void Function()? onDone,
+    bool? cancelOnError,
+  }) {
+    return _streamController.stream.listen(
+      onData,
+      onError: (error) {
+        if (error is Exception) {
+          _error = error;
+        }
+        // ignore: avoid_dynamic_calls
+        onError?.call(error);
+      },
+      onDone: () {
+        _done = true;
+        onDone?.call();
+      },
+    );
+  }
+
+  @override
+  Future<void> stop() async {
+    if (!_streamController.isClosed) {
+      await _streamController.close();
+    }
+    _done = true;
+  }
+}

lib/src/core/wot.dart

@@ -10,7 +10,8 @@ import '../scripting_api/discovery/discovery_method.dart';
 import 'consumed_thing.dart';
 import 'exposed_thing.dart';
 import 'servient.dart';
-import 'thing_discovery.dart' show ThingDiscovery;
+import 'thing_discovery.dart'
+    show DiscoveryException, ThingDiscovery, ThingDiscoveryProcess;
 
 /// This [Exception] is thrown if an error during the consumption of a
 /// [ThingDescription] occurs.
@@ -95,4 +96,30 @@ class WoT implements scripting_api.WoT {
   Future<ThingDescription> requestThingDescription(Uri url) {
     return _servient.requestThingDescription(url);
   }
+
+  @override
+  Future<scripting_api.ThingDiscoveryProcess> exploreDirectory(
+    Uri url, [
+    scripting_api.ThingFilter? filter,
+  ]) async {
+    // TODO: Could also be moved to the Servient level
+    final directoryThingDescription = await requestThingDescription(url);
+    final consumedDirectoryThing = await consume(directoryThingDescription);
+
+    final interactionOutput =
+        await consumedDirectoryThing.readProperty('things');
+    final rawThingDescriptions = await interactionOutput.value();
+
+    if (rawThingDescriptions is! List<dynamic>) {
+      throw DiscoveryException(
+        'Received an invalid output during Directory discovery.',
+      );
+    }
+
+    final thingDescriptionStream = Stream.fromIterable(
+      rawThingDescriptions.whereType<Map<String, dynamic>>(),
+    ).map(ThingDescription.fromJson);
+
+    return ThingDiscoveryProcess(thingDescriptionStream, filter);
+  }
 }

lib/src/scripting_api/discovery/thing_discovery.dart

@@ -22,3 +22,23 @@ abstract interface class ThingDiscovery implements Stream<ThingDescription> {
   /// Stops the discovery process.
   void stop();
 }
+
+/// Provides the properties and methods controlling the discovery process, and
+/// returning the results.
+abstract interface class ThingDiscoveryProcess
+    implements Stream<ThingDescription> {
+  /// The [thingFilter] that is applied during the discovery process.
+  ThingFilter? get thingFilter;
+
+  /// `true` if the discovery has been stopped or completed with no more results
+  /// to report.
+  bool get done;
+
+  /// Represents the last error that occurred during the discovery process.
+  ///
+  /// Typically used for critical errors that stop discovery.
+  Exception? get error;
+
+  /// Stops the discovery process.
+  void stop();
+}

lib/src/scripting_api/wot.dart

@@ -34,6 +34,14 @@ abstract interface class WoT {
   /// Requests a [ThingDescription] from the given [url].
   Future<ThingDescription> requestThingDescription(Uri url);
 
+  /// Starts the discovery process that given a TD Directory [url], will provide
+  /// [ThingDescription] objects for Thing Descriptions that match an optional
+  /// [filter] argument of type [ThingFilter].
+  Future<ThingDiscoveryProcess> exploreDirectory(
+    Uri url, [
+    ThingFilter? filter,
+  ]);
+
   /// Discovers [ThingDescription]s from a given [url] using the specified
   /// [method].
   ///