db: Write a first Drift schema

Also add a .gitattributes file, excluding `*.g.dart` files from
diffs.  We didn't really need this when the only such files were
the JSON serialization/deserialization files in the API bindings,
because those are pretty compact; but this generated ORM code is
much longer and makes it more necessary.

Author: gnprice

.gitattributes

@@ -0,0 +1,9 @@
+# Suppress noisy generated files in diffs.
+
+# Dart files generated from the files next to them:
+*.g.dart -diff
+
+# On the other hand, keep diffs for pubspec.lock.  It contains
+# information independent of any non-generated file in the tree.
+# And thankfully it's much less verbose than, say, a yarn.lock.
+#pubspec.lock -diff

lib/model/database.dart

@@ -0,0 +1,58 @@
+import 'dart:io';
+
+import 'package:drift/drift.dart';
+import 'package:drift/native.dart';
+import 'package:path/path.dart' as path;
+import 'package:path_provider/path_provider.dart';
+
+part 'database.g.dart';
+
+// TODO unify with Account in store.dart
+class Accounts extends Table {
+  Column<int>    get id => integer().autoIncrement()();
+
+  Column<String> get realmUrl => text().map(const UriConverter())();
+  Column<int>    get userId => integer()();
+
+  Column<String> get email => text()();
+  Column<String> get apiKey => text()();
+
+  Column<String> get zulipVersion => text()();
+  Column<String> get zulipMergeBase => text().nullable()();
+  Column<int>    get zulipFeatureLevel => integer()();
+
+  @override
+  List<Set<Column<Object>>> get uniqueKeys => [
+    {realmUrl, userId},
+    {realmUrl, email},
+  ];
+}
+
+class UriConverter extends TypeConverter<Uri, String> {
+  const UriConverter();
+  @override String toSql(Uri value) => value.toString();
+  @override Uri fromSql(String fromDb) => Uri.parse(fromDb);
+}
+
+LazyDatabase _openConnection() {
+  return LazyDatabase(() async {
+    // TODO decide if this path is the right one to use
+    final dbFolder = await getApplicationDocumentsDirectory();
+    final file = File(path.join(dbFolder.path, 'db.sqlite'));
+    return NativeDatabase.createInBackground(file);
+  });
+}
+
+@DriftDatabase(tables: [Accounts])
+class AppDatabase extends _$AppDatabase {
+  AppDatabase(QueryExecutor e) : super(e);
+
+  AppDatabase.live() : this(_openConnection());
+
+  @override
+  int get schemaVersion => 1; // TODO migrations
+
+  Future<int> createAccount(AccountsCompanion values) {
+    return into(accounts).insert(values);
+  }
+}