feat(curator): curate update keeps a server's dictionaries current

EDRDG's licence asks of servers showing its dictionaries that they update
them at least monthly. `curate update --into <folder>` downloads EDRDG's
files of the day (JMdict with Tatoeba's sentences, KANJIDIC2), converts
them with the JLPT levels the curator now brings along (yomitan-jlpt-vocab's
lists, CC BY-SA 4.0, and the kanji levels of kanji-data's kanji.json: both
static, in data/ with their origin), and puts each file in place at once
(written beside it as .part, then renamed over it), so the server never
reads half a file; a failure leaves the files as they were. With --every 7
it keeps running and updates whenever the files are a week old, as their
dates say, so a restart doesn't download again; after a failure it tries
again in six hours. A real update takes some 50 seconds and 400 MB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMm7usAo6q9ZZRoPkWjoxi
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_curator/test/update_test.dart

@@ -0,0 +1,84 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:halkyon_learn_curator/src/update.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late Directory into;
+
+  setUp(() => into = Directory.systemTemp.createTempSync('dictionaries'));
+  tearDown(() => into.deleteSync(recursive: true));
+
+  /// Fetches the samples in place of EDRDG's files of the day.
+  Future<void> samples(Uri uri, File file) async {
+    final sample = uri == jmdictSource
+        ? 'test/fixtures/jmdict-e-examp-sample.xml'
+        : 'test/fixtures/kanjidic2-sample.xml';
+    await file.writeAsBytes(gzip.encode(await File(sample).readAsBytes()));
+  }
+
+  /// The header of the dictionary file [name] in [into].
+  Map<String, Object?> header(String name) => jsonDecode(
+    utf8
+        .decode(gzip.decode(File('${into.path}/$name').readAsBytesSync()))
+        .split('\n')
+        .first,
+  ) as Map<String, Object?>;
+
+  test("writes JMdict and KANJIDIC2 from EDRDG's files, the JLPT levels from "
+      "the curator's data", () async {
+    final written = await updateDictionaries(
+      into: into,
+      data: Directory('data'),
+      fetch: samples,
+    );
+
+    expect(
+      [for (final file in written) file.uri.pathSegments.last],
+      ['jmdict-en.jsonl.gz', 'kanjidic-en.jsonl.gz'],
+    );
+    expect(header('jmdict-en.jsonl.gz')['sourceVersion'], '2026-10-09');
+    expect(
+      [
+        for (final credit in header('jmdict-en.jsonl.gz')['credits']! as List)
+          (credit as Map)['name'],
+      ],
+      ['JMdict', 'JLPT vocabulary lists', 'Tatoeba'],
+    );
+    expect(header('kanjidic-en.jsonl.gz')['kind'], 'characters');
+    // Nothing half-written left behind.
+    expect(
+      [for (final entity in into.listSync()) entity.uri.pathSegments.last]
+        ..sort(),
+      ['jmdict-en.jsonl.gz', 'kanjidic-en.jsonl.gz'],
+    );
+    expect(lastUpdated(into), isNotNull);
+  });
+
+  test('a download that fails leaves the files there as they were', () async {
+    await updateDictionaries(
+      into: into,
+      data: Directory('data'),
+      fetch: samples,
+    );
+    final before = File('${into.path}/jmdict-en.jsonl.gz').readAsBytesSync();
+
+    await expectLater(
+      updateDictionaries(
+        into: into,
+        data: Directory('data'),
+        fetch: (uri, file) => uri == kanjidicSource
+            ? Future.error(const HttpException('EDRDG answered 503.'))
+            : samples(uri, file),
+      ),
+      throwsA(isA<HttpException>()),
+    );
+
+    expect(File('${into.path}/jmdict-en.jsonl.gz').readAsBytesSync(), before);
+  });
+
+  test('a folder missing a file was never brought up to date', () {
+    expect(lastUpdated(into), isNull);
+  });
+}