tool: begin parsing OpenAPI specification

tool/src/json_map.dart

@@ -0,0 +1,85 @@
+/// Type definition for JSON data.
+typedef JsonMap = Map<String, Object?>;
+
+/// Type definition of a [JsonMap] key.
+typedef JsonMapEntry = MapEntry<String, Object?>;
+
+/// Helpers for accessing JSON data.
+extension JsonMapValue on JsonMap {
+  /// Retrieve a [bool] at the given [key].
+  ///
+  /// Returns [defaultTo] if the [key] is not present.
+  bool getBool(String key, {bool defaultTo = false}) =>
+      this[key] as bool? ?? defaultTo;
+
+  /// Retrieve a [String] at the given [key].
+  ///
+  /// Returns [defaultTo] if the [key] is not present.
+  String getString(String key, {String defaultTo = ''}) =>
+      this[key] as String? ?? defaultTo;
+
+  /// Retrieves a [List] at the given [key].
+  ///
+  /// Single values of [T] are turned into a [List] containing a single value.
+  /// If the [key] is not present an empty [List] is returned.
+  List<T> getList<T>(String key, {List<T> defaultTo = const []}) {
+    final value = this[key];
+
+    if (value == null) {
+      return defaultTo;
+    }
+
+    if (value is List<T>) {
+      return value;
+    }
+
+    return value is List ? value.cast<T>() : <T>[value as T];
+  }
+
+  /// Retrieves a [Map] at the given [key].
+  ///
+  /// If the [key] is not present an empty [Map] is returned.
+  Map<K, V> getMap<K, V>(String key, {Map<K, V> defaultTo = const {}}) {
+    final value = this[key] as Map?;
+
+    if (value == null) {
+      return defaultTo;
+    }
+
+    if (value is Map<K, V>) {
+      return value;
+    }
+
+    return value.cast<K, V>();
+  }
+
+  /// Retrieve a [List] of [Map]s at the given [key].
+  ///
+  /// If the [key] is not present an empty [Map] is returned.
+  List<Map<K, V>> getMapList<K, V>(
+    String key, {
+    List<Map<K, V>> defaultTo = const [],
+  }) {
+    final list = this[key] as List?;
+
+    if (list == null) {
+      return defaultTo;
+    }
+
+    if (list is List<Map<K, V>>) {
+      return list;
+    }
+
+    return list.map((m) => (m as Map).cast<K, V>()).toList();
+  }
+
+  /// Retrieve a [JsonMap] at the given [key].
+  ///
+  /// Uses [getMap] with the expected type parameters.
+  JsonMap getJson(String key) => getMap<String, Object?>(key);
+
+  /// Retrieve a [List] of [JsonMap]s at the given [key].
+  ///
+  /// Uses [getMap] with the expected type parameters.
+  List<JsonMap> getJsonList(String key) => getMapList<String, Object?>(key);
+}

tool/src/schema.dart

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+/// A set of `extension`s over the underlying JSON data that presents a typed
+/// API for the OpenAPI specification.
+library;
+
+import 'json_map.dart';
+
+/// Extension presenting the root of the OpenAPI schema.
+extension OpenApiSchema on JsonMap {
+  static const String _openApi = 'openapi';
+  static const String _info = 'info';
+
+  /// The OpenAPI version.
+  String get openApiVersion => getString(_openApi);
+
+  /// Retrieves the [OpenApiInfoSchema].
+  JsonMap get info => getJson(_info);
+}
+
+/// Extension presenting the `info` schema.
+///
+/// Corresponds to
+///     info:
+extension OpenApiInfoSchema on JsonMap {
+  static const String _title = 'title';
+  static const String _version = 'version';
+
+  /// The title of the schema definition.
+  String get title => getString(_title);
+
+  /// The version of the schema definition.
+  String get version => getString(_version);
+}