Add widget to display the thumbnails of memories

lib/ui/memories_widget.dart

@@ -0,0 +1,110 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+import 'package:photos/memory_service.dart';
+import 'package:photos/models/memory.dart';
+import 'package:photos/ui/thumbnail_widget.dart';
+
+class MemoriesWidget extends StatefulWidget {
+  MemoriesWidget({Key key}) : super(key: key);
+
+  @override
+  _MemoriesWidgetState createState() => _MemoriesWidgetState();
+}
+
+class _MemoriesWidgetState extends State<MemoriesWidget> {
+  @override
+  Widget build(BuildContext context) {
+    return FutureBuilder<List<Memory>>(
+      future: MemoryService.instance.getMemories(),
+      builder: (context, snapshot) {
+        if (snapshot.hasError ||
+            !snapshot.hasData ||
+            snapshot.data.length == 0) {
+          return Container();
+        } else {
+          return _buildMemories(snapshot.data);
+        }
+      },
+    );
+  }
+
+  Widget _buildMemories(List<Memory> memories) {
+    final collatedMemories = _collateMemories(memories);
+    final memoryWidgets = List<Widget>();
+    for (final memories in collatedMemories) {
+      memoryWidgets.add(MemoryWidget(memories: memories));
+    }
+    return Row(children: memoryWidgets);
+  }
+
+  List<List<Memory>> _collateMemories(List<Memory> memories) {
+    final yearlyMemories = List<Memory>();
+    final collatedMemories = List<List<Memory>>();
+    for (int index = 0; index < memories.length; index++) {
+      if (index > 0 &&
+          !_areMemoriesFromSameYear(memories[index - 1], memories[index])) {
+        final collatedYearlyMemories = List<Memory>();
+        collatedYearlyMemories.addAll(yearlyMemories);
+        collatedMemories.add(collatedYearlyMemories);
+        yearlyMemories.clear();
+      }
+      yearlyMemories.add(memories[index]);
+    }
+    if (yearlyMemories.isNotEmpty) {
+      collatedMemories.add(yearlyMemories);
+    }
+    return collatedMemories;
+  }
+
+  bool _areMemoriesFromSameYear(Memory first, Memory second) {
+    var firstDate =
+        DateTime.fromMicrosecondsSinceEpoch(first.file.creationTime);
+    var secondDate =
+        DateTime.fromMicrosecondsSinceEpoch(second.file.creationTime);
+    return firstDate.year == secondDate.year;
+  }
+}
+
+class MemoryWidget extends StatelessWidget {
+  const MemoryWidget({
+    Key key,
+    @required this.memories,
+  }) : super(key: key);
+
+  final List<Memory> memories;
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      width: 100,
+      height: 120,
+      child: Padding(
+        padding: const EdgeInsets.all(8.0),
+        child: Column(
+          children: [
+            ClipOval(
+              child: Container(
+                width: 76,
+                height: 76,
+                child: ThumbnailWidget(memories[0].file),
+              ),
+            ),
+            Padding(padding: EdgeInsets.all(2)),
+            _getTitle(memories[0]),
+          ],
+        ),
+      ),
+    );
+  }
+
+  Text _getTitle(Memory memory) {
+    final present = DateTime.now();
+    final then = DateTime.fromMicrosecondsSinceEpoch(memory.file.creationTime);
+    final diffInYears = present.year - then.year;
+    if (diffInYears == 1) {
+      return Text("1 year ago");
+    } else {
+      return Text(diffInYears.toString() + " years ago");
+    }
+  }
+}