Add service to view and mark memories as seen

lib/memory_service.dart

@@ -0,0 +1,49 @@
+import 'package:logging/logging.dart';
+import 'package:photos/db/files_db.dart';
+import 'package:photos/db/memories_db.dart';
+import 'package:photos/models/file.dart';
+import 'package:photos/models/memory.dart';
+
+class MemoryService {
+  final _logger = Logger("MemoryService");
+  final _memoriesDB = MemoriesDB.instance;
+  final _filesDB = FilesDB.instance;
+  static final microSecondsInADay = 86400000000;
+  static final daysInAYear = 365;
+  static final daysBefore = 7;
+  static final daysAfter = 1;
+
+  MemoryService._privateConstructor();
+
+  static final MemoryService instance = MemoryService._privateConstructor();
+
+  Future<void> sync() async {
+    await _memoriesDB.clearMemoriesSeenBeforeTime(
+        DateTime.now().microsecondsSinceEpoch - (7 * microSecondsInADay));
+  }
+
+  Future<List<Memory>> getMemories() async {
+    final files = List<File>();
+    for (var yearAgo = 1; yearAgo <= 100; yearAgo++) {
+      var now = DateTime.now().microsecondsSinceEpoch;
+      var checkPointDay = yearAgo * daysInAYear;
+      final startCreationTime =
+          now - ((checkPointDay - daysBefore) * microSecondsInADay);
+      final endCreationTime =
+          now - ((checkPointDay + daysAfter) * microSecondsInADay);
+      files.addAll(await _filesDB.getFilesCreatedWithinDuration(
+          startCreationTime, endCreationTime));
+    }
+    final seenFileIDs = await _memoriesDB.getSeenFileIDs();
+    final memories = List<Memory>();
+    for (final file in files) {
+      memories.add(Memory(file, seenFileIDs.contains(file.generatedId)));
+    }
+    return memories;
+  }
+
+  Future markMemoryAsSeen(Memory memory) async {
+    return _memoriesDB.markMemoryAsSeen(
+        memory, DateTime.now().microsecondsSinceEpoch);
+  }
+}

lib/models/memory.dart

@@ -4,7 +4,7 @@ class Memory {
   final File file;
   bool _isSeen;
 
-  Memory(this.file);
+  Memory(this.file, this._isSeen);
 
   bool isSeen() {
     return _isSeen;