Halkyon's shared packages

A pub workspace of the Dart packages Halkyon's apps share: halkyon_ui,
Halkyon's look (the theme, fonts, layout and shared widgets, with texts
in English and German), halkyon_core's low-level primitives and
halkyon_interop's cross-app contracts. Dart 3.13 with LeanCode's lints,
configured once at the root; apps take a package by git, pinned to a
signed commit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_core/lib/src/exceptions.dart

@@ -0,0 +1,11 @@
+/// Marker interface for exceptions originating in Halkyon code.
+///
+/// Implementing this is optional. It exists so callers can distinguish
+/// "this came from Halkyon" from "this came from a library we use" using
+/// `on HalkyonException catch (e)` if they want that granularity.
+///
+/// Most Halkyon exceptions should also extend a more specific type
+/// (e.g., `AuthException`, `SyncException`) defined in the relevant feature.
+abstract class HalkyonException() implements Exception {
+  String get message;
+}

packages/halkyon_core/lib/src/logger.dart

@@ -0,0 +1,54 @@
+/// Severity levels for log messages.
+enum LogLevel() {
+  debug,
+  info,
+  warning,
+  error,
+}
+
+/// A minimal logging interface.
+///
+/// Implementations are injected via the app's `Dependencies` composition root
+/// rather than imported globally, so tests can swap in fakes.
+abstract interface class Logger() {
+  void log(
+    LogLevel level,
+    String message, {
+    Object? error,
+    StackTrace? stackTrace,
+  });
+}
+
+/// A logger that writes to stdout. Suitable for development and tests.
+///
+/// Production apps should use a logger that forwards to Sentry or similar,
+/// configured at the composition root.
+class const ConsoleLogger() implements Logger {
+  @override
+  void log(
+    LogLevel level,
+    String message, {
+    Object? error,
+    StackTrace? stackTrace,
+  }) {
+    final prefix = switch (level) {
+      LogLevel.debug => '[DEBUG]',
+      LogLevel.info => '[INFO]',
+      LogLevel.warning => '[WARN]',
+      LogLevel.error => '[ERROR]',
+    };
+    // Writing to stdout is this logger's whole purpose.
+    // ignore: avoid_print
+    print('$prefix $message');
+    if (error != null) {
+      // As above: stdout is where this logger writes.
+      // ignore: avoid_print
+      print('  error: $error');
+    }
+    if (stackTrace != null) {
+      // As above: stdout is where this logger writes.
+      // ignore: avoid_print
+      print('  stack: $stackTrace');
+    }
+  }
+}

packages/halkyon_core/lib/src/uuid.dart

@@ -0,0 +1,10 @@
+import 'package:uuid/uuid.dart';
+
+const _uuid = Uuid();
+
+/// Generates a v4 (random) UUID as a lowercase hyphenated string.
+///
+/// Thin wrapper over `package:uuid` so Halkyon code doesn't need to import
+/// it directly. If we ever need to swap the UUID library, this is the only
+/// site that changes.
+String generateUuid() => _uuid.v4();