Add a data store to persist user keys

lib/db/public_keys_db.dart

@@ -0,0 +1,75 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:path/path.dart';
+import 'package:sqflite/sqflite.dart';
+import 'package:path_provider/path_provider.dart';
+
+class PublicKeysDB {
+  static final _databaseName = "ente.public_keys.db";
+  static final _databaseVersion = 1;
+
+  static final table = 'public_keys';
+
+  static final columnEmail = 'email';
+  static final columnPublicKey = 'public_key';
+
+  PublicKeysDB._privateConstructor();
+  static final PublicKeysDB instance = PublicKeysDB._privateConstructor();
+
+  static Database _database;
+  Future<Database> get database async {
+    if (_database != null) return _database;
+    _database = await _initDatabase();
+    return _database;
+  }
+
+  _initDatabase() async {
+    Directory documentsDirectory = await getApplicationDocumentsDirectory();
+    String path = join(documentsDirectory.path, _databaseName);
+    return await openDatabase(
+      path,
+      version: _databaseVersion,
+      onCreate: _onCreate,
+    );
+  }
+
+  Future _onCreate(Database db, int version) async {
+    await db.execute('''
+                CREATE TABLE $table (
+                  $columnEmail TEXT PRIMARY KEY NOT NULL,
+                  $columnPublicKey TEXT NOT NULL
+                )
+                ''');
+  }
+
+  Future<int> setKey(String email, String publicKey) async {
+    final db = await instance.database;
+    return db.insert(table, _getRow(email, publicKey),
+        conflictAlgorithm: ConflictAlgorithm.replace);
+  }
+
+  Future<Map<String, String>> searchByEmail(String email) async {
+    final db = await instance.database;
+    return _convertRows(await db.query(
+      table,
+      where: '$columnEmail LIKE %?%',
+      whereArgs: [email],
+    ));
+  }
+
+  Map<String, dynamic> _getRow(String email, String publicKey) {
+    var row = new Map<String, dynamic>();
+    row[columnEmail] = email;
+    row[columnPublicKey] = publicKey;
+    return row;
+  }
+
+  Map<String, String> _convertRows(List<Map<String, dynamic>> rows) {
+    final keys = Map<String, String>();
+    for (final row in rows) {
+      keys[row[columnEmail]] = row[columnPublicKey];
+    }
+    return keys;
+  }
+}