Add storage layer for memories

lib/db/memories_db.dart

@@ -0,0 +1,80 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:path/path.dart';
+import 'package:photos/models/memory.dart';
+import 'package:sqflite/sqflite.dart';
+import 'package:path_provider/path_provider.dart';
+
+class MemoriesDB {
+  static final _databaseName = "ente.memories.db";
+  static final _databaseVersion = 1;
+
+  static final table = 'memories';
+
+  static final columnFileId = 'file_id';
+  static final columnSeenTime = 'seen_time';
+
+  MemoriesDB._privateConstructor();
+  static final MemoriesDB instance = MemoriesDB._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 (
+                  $columnFileId INTEGER PRIMARY KEY NOT NULL,
+                  $columnSeenTime TEXT NOT NULL
+                )
+                ''');
+  }
+
+  Future<int> clearMemoriesSeenBeforeTime(int timestamp) async {
+    final db = await instance.database;
+    return db.delete(
+      table,
+      where: '$columnSeenTime < ',
+      whereArgs: [timestamp],
+    );
+  }
+
+  Future<int> markMemoryAsSeen(Memory memory, int timestamp) async {
+    final db = await instance.database;
+    return await db.insert(table, _getRowForSeenMemory(memory, timestamp),
+        conflictAlgorithm: ConflictAlgorithm.replace);
+  }
+
+  Future<List<int>> getSeenFileIDs() async {
+    final db = await instance.database;
+    return _convertToFileIDs(await db.query(table));
+  }
+
+  Map<String, dynamic> _getRowForSeenMemory(Memory memory, int timestamp) {
+    var row = new Map<String, dynamic>();
+    row[columnFileId] = memory.file.generatedId;
+    row[columnSeenTime] = timestamp;
+    return row;
+  }
+
+  _convertToFileIDs(List<Map<String, dynamic>> rows) {
+    final fileIDs = List<int>();
+    for (final row in rows) {
+      fileIDs.add(int.parse(row[columnFileId]));
+    }
+  }
+}

lib/models/memory.dart

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+import 'package:photos/models/file.dart';
+
+class Memory {
+  final File file;
+  bool _isSeen;
+
+  Memory(this.file);
+
+  bool isSeen() {
+    return _isSeen;
+  }
+
+  bool markSeen() {
+    _isSeen = true;
+  }
+}