Add Title + FileName sorting modes

lib/core/sorting_mode.dart

@@ -5,6 +5,8 @@ typedef NoteSortingFunction = int Function(Note a, Note b);
 class SortingMode {
   static const Modified = SortingMode("Last Modified", "Modified");
   static const Created = SortingMode("Created", "Created");
+  static const FileName = SortingMode("File Name", "FileName");
+  static const Title = SortingMode("Title", "Title");
   static const Default = Modified;
 
   final String _str;
@@ -22,6 +24,8 @@ class SortingMode {
   static const options = <SortingMode>[
     Modified,
     Created,
+    FileName,
+    Title,
   ];
 
   static SortingMode fromInternalString(String str) {
@@ -67,6 +71,28 @@ class SortingMode {
           return bDt.compareTo(aDt);
         };
 
+      case "Title":
+        return (Note a, Note b) {
+          var aTitleExists = a.title != null && a.title.isNotEmpty;
+          var bTitleExists = b.title != null && b.title.isNotEmpty;
+
+          if (!aTitleExists && bTitleExists) {
+            return 1;
+          }
+          if (aTitleExists && !bTitleExists) {
+            return -1;
+          }
+          if (!aTitleExists && !bTitleExists) {
+            return a.fileName.compareTo(b.fileName);
+          }
+          return a.title.compareTo(b.title);
+        };
+
+      case "FileName":
+        return (Note a, Note b) {
+          return a.fileName.compareTo(b.fileName);
+        };
+
       case "Modified":
       default:
         return (Note a, Note b) {

lib/folder_views/journal_view.dart

@@ -38,10 +38,10 @@ class JournalView extends StatelessWidget {
 
     DateTime date;
     var sortingMode = folder.config.sortingMode;
-    if (sortingMode == SortingMode.Modified) {
+    if (sortingMode == SortingMode.Created) {
-      date = note.modified;
-    } else if (sortingMode == SortingMode.Created) {
       date = note.created;
+    } else {
+      date = note.modified;
     }
 
     if (date != null) {

lib/screens/folder_view.dart

@@ -227,23 +227,24 @@ class _FolderViewState extends State<FolderView> {
     Navigator.of(context).push(route);
   }
 
+  RadioListTile<SortingMode> _buildSortingTile(SortingMode sm) {
+    return RadioListTile<SortingMode>(
+      title: Text(sm.toPublicString()),
+      value: sm,
+      groupValue: sortedNotesFolder.sortingMode,
+      onChanged: (SortingMode sm) => Navigator.of(context).pop(sm),
+    );
+  }
+
   void _sortButtonPressed() async {
     var newSortingMode = await showDialog<SortingMode>(
       context: context,
       builder: (BuildContext context) {
         var children = <Widget>[
-          RadioListTile<SortingMode>(
+          _buildSortingTile(SortingMode.Modified),
-            title: const Text("Last Modified"),
+          _buildSortingTile(SortingMode.Created),
-            value: SortingMode.Modified,
+          _buildSortingTile(SortingMode.Title),
-            groupValue: sortedNotesFolder.sortingMode,
+          _buildSortingTile(SortingMode.FileName),
-            onChanged: (SortingMode sm) => Navigator.of(context).pop(sm),
-          ),
-          RadioListTile<SortingMode>(
-            title: const Text("Created"),
-            value: SortingMode.Created,
-            groupValue: sortedNotesFolder.sortingMode,
-            onChanged: (SortingMode sm) => Navigator.of(context).pop(sm),
-          ),
         ];
 
         return AlertDialog(