feat: Add package:cedar (#63)

Adds `package:cedar` which includes Dart representations of the Cedar policy language and shared interfaces which will be implemented in `package:cedar_ffi`.

packages/cedar/.gitignore

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+# https://dart.dev/guides/libraries/private-files
+# Created by `dart pub`
+.dart_tool/
+
+# Avoid committing pubspec.lock for library packages; see
+# https://dart.dev/guides/libraries/private-files#pubspeclock.
+pubspec.lock

packages/cedar/CHANGELOG.md

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+## 0.1.0
+
+- Initial version.

packages/cedar/README.md

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+# cedar
+
+Core types and interfaces of the [Cedar](https://www.cedarpolicy.com/en) policy language in Dart.
+
+Cedar is a policy language for defining and enforcing access control policies in a declarative way. It is used in [Celest](https://celest.dev) for ensuring that only authorized users meeting certain criteria can access your backend.
+
+The actual implementation of the Cedar engine is in [cedar_ffi](https://pub.dev/packages/cedar_ffi), which uses FFI and Dart's native assets feature to bind to the Rust implementation of Cedar. This package only holds the Dart AST representation and is separate from `package:cedar_ffi` so that the types can be used without bundling the native assets of `package:cedar_ffi`.

packages/cedar/analysis_options.yaml

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+include: package:lints/recommended.yaml

packages/cedar/lib/cedar.dart

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+/// Core types and interfaces of the [Cedar](https://www.cedarpolicy.com/en)
+/// policy language in Dart.
+///
+/// Cedar is a policy language for defining and enforcing access control
+/// policies in a declarative way. It is used in [Celest](https://celest.dev)
+/// for ensuring that only authorized users meeting certain criteria can access
+/// your backend.
+///
+/// The actual implementation of the Cedar engine is in
+/// [cedar_ffi](https://pub.dev/packages/cedar_ffi), which uses FFI and Dart's
+/// native assets feature to bind to the Rust implementation of Cedar. This
+/// package only holds the Dart AST representation and is separate from
+/// `package:cedar_ffi` so that the types can be used without bundling the
+/// native assets of `package:cedar_ffi`.
+library;
+
+export 'src/ast/cedar_entity.dart';
+export 'src/ast/cedar_entity_id.dart';
+export 'src/ast/cedar_schema.dart';
+export 'src/authorization/cedar_authorization_request.dart';
+export 'src/authorization/cedar_authorization_response.dart';
+export 'src/authorization/cedar_authorizer.dart';
+export 'src/policy/cedar_policy.dart';
+export 'src/policy/cedar_policy_set.dart';
+export 'src/policy/json_expr.dart';
+export 'src/serializers.dart';

packages/cedar/lib/src/ast/cedar_entity.dart

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+import 'package:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+import 'package:built_value/serializer.dart';
+import 'package:cedar/src/ast/cedar_entity_id.dart';
+import 'package:cedar/src/policy/json_expr.dart';
+
+part 'cedar_entity.g.dart';
+
+/// Dart representation of a Cedar [entity](https://docs.cedarpolicy.com/policies/syntax-entity.html).
+///
+/// Conforms to the entity [JSON format](https://docs.cedarpolicy.com/auth/entities-syntax.html#entities).
+abstract class CedarEntity implements Built<CedarEntity, CedarEntityBuilder> {
+  factory CedarEntity({
+    required CedarEntityId id,
+    List<CedarEntityId> parents = const [],
+    Map<String, CedarValueJson> attributes = const {},
+  }) {
+    return _$CedarEntity._(
+      id: id,
+      parents: parents.build(),
+      attributes: attributes.build(),
+    );
+  }
+
+  factory CedarEntity.build([
+    void Function(CedarEntityBuilder) updates,
+  ]) = _$CedarEntity;
+
+  factory CedarEntity.fromJson(Map<String, Object?> json) => CedarEntity(
+        id: CedarEntityId.fromJson(json['uid'] as Map<String, Object?>),
+        parents: (json['parents'] as List<Object?>)
+            .map((e) => CedarEntityId.fromJson(e as Map<String, Object?>))
+            .toList(),
+        attributes: (json['attrs'] as Map<Object?, Object?>)
+            .cast<String, Object?>()
+            .map((key, value) => MapEntry(key, CedarValueJson.fromJson(value))),
+      );
+
+  const CedarEntity._();
+
+  CedarEntityId get id;
+  BuiltList<CedarEntityId> get parents;
+  BuiltMap<String, CedarValueJson> get attributes;
+
+  Map<String, Object?> toJson() => {
+        'uid': id.toJson(),
+        'parents': parents.map((e) => e.toJson()).toList(),
+        'attrs': attributes
+            .map((key, value) => MapEntry(key, value.toJson()))
+            .asMap(),
+      };
+
+  static Serializer<CedarEntity> get serializer => _$cedarEntitySerializer;
+}

packages/cedar/lib/src/ast/cedar_entity_id.dart

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+import 'package:built_value/built_value.dart';
+import 'package:built_value/serializer.dart';
+
+part 'cedar_entity_id.g.dart';
+
+abstract class CedarEntityId
+    implements Built<CedarEntityId, CedarEntityIdBuilder> {
+  factory CedarEntityId(String type, String id) =>
+      _$CedarEntityId._(type: type, id: id);
+
+  factory CedarEntityId.build([
+    void Function(CedarEntityIdBuilder) updates,
+  ]) = _$CedarEntityId;
+
+  factory CedarEntityId.fromJson(Map<String, Object?> json) {
+    switch (json) {
+      case {'type': final String type, 'id': final String id} ||
+            {'__entity': {'type': final String type, 'id': final String id}}:
+        return CedarEntityId(type, id);
+      default:
+        throw FormatException('Invalid entity ID JSON: $json');
+    }
+  }
+
+  const CedarEntityId._();
+
+  String get type;
+  String get id;
+
+  /// Returns a normalized version of this entity ID.
+  ///
+  /// Cedar prohibits whitespace in entity IDs, so this method removes all
+  /// whitespace from the [type] and [id].
+  ///
+  /// See Cedar [RFC 9](https://github.com/cedar-policy/rfcs/blob/main/text/0009-disallow-whitespace-in-entityuid.md)
+  /// for more information.
+  CedarEntityId get normalized => CedarEntityId(
+        type,
+        String.fromCharCodes(
+          id.runes.expand((char) {
+            return switch (char) {
+              0 => '\\0'.codeUnits,
+              0x9 => '\\t'.codeUnits,
+              0xa => '\\n'.codeUnits,
+              0xd => '\\r'.codeUnits,
+              0x22 => '\\"'.codeUnits,
+              0x27 => "\\'".codeUnits,
+              < 0x20 ||
+              0x7f || // Delete
+              0x96 || // Non-breaking space
+              > 0xffff =>
+                '\\u{${char.toRadixString(16)}}'.codeUnits,
+              _ => [char],
+            };
+          }),
+        ),
+      );
+
+  @override
+  String toString() => '$type::"$id"';
+
+  Map<String, Object?> toJson() => {
+        'type': type,
+        'id': id,
+      };
+
+  static Serializer<CedarEntityId> get serializer => _$cedarEntityIdSerializer;
+}