Allow the Note FileName to be configured

This is super ugly, but it solves a real use case, and hopefully I'll
eventually get around to improving the UI of the Settings page.

lib/datetime_utils.dart

@@ -1,5 +1,9 @@
 import 'package:intl/intl.dart';
 
+String toIso8601(DateTime dt) {
+  return DateFormat("yyyy-MM-ddTHH:mm:ss").format(dt);
+}
+
 String toIso8601WithTimezone(DateTime dt) {
   var result = DateFormat("yyyy-MM-ddTHH:mm:ss").format(dt);
 

lib/note_fileName.dart

@@ -0,0 +1,16 @@
+import 'package:journal/note.dart';
+import 'package:journal/datetime_utils.dart';
+import 'package:journal/settings.dart';
+
+String getFileName(Note note) {
+  switch (Settings.instance.noteFileNameFormat) {
+    case NoteFileNameFormat.Iso8601:
+      return toIso8601(note.created) + ".md";
+    case NoteFileNameFormat.Iso8601WithTimeZone:
+      return toIso8601WithTimezone(note.created) + ".md";
+    case NoteFileNameFormat.Iso8601WithTimeZoneWithoutColon:
+      return toIso8601WithTimezone(note.created).replaceAll(":", "_") + ".md";
+  }
+
+  return note.created.toString();
+}

lib/screens/settings_screen.dart

@@ -183,6 +183,35 @@ class SettingsListState extends State<SettingsList> {
       ListTile(title: gitAuthorForm),
       ListTile(title: gitAuthorEmailForm),
       SizedBox(height: 16.0),
+      PreferenceTitle("Storage"),
+      DropdownPreference(
+        'File Name',
+        'file_name',
+        defaultVal: "ISO8601 With TimeZone",
+        values: [
+          "ISO8601 With TimeZone",
+          "ISO8601",
+          "ISO8601 without Colons",
+        ],
+        onChange: (newVal) {
+          NoteFileNameFormat format;
+          switch (newVal) {
+            case "ISO8601 With TimeZone":
+              format = NoteFileNameFormat.Iso8601WithTimeZone;
+              break;
+            case "ISO8601":
+              format = NoteFileNameFormat.Iso8601;
+              break;
+            case "ISO8601 without Colons":
+              format = NoteFileNameFormat.Iso8601WithTimeZoneWithoutColon;
+              break;
+            default:
+              format = NoteFileNameFormat.Iso8601WithTimeZone;
+          }
+          Settings.instance.noteFileNameFormat = format;
+          Settings.instance.save();
+        },
+      ),
       VersionNumberTile(),
     ]);
   }

lib/state_container.dart

@@ -7,8 +7,8 @@ import 'package:flutter/material.dart';
 import 'package:journal/analytics.dart';
 import 'package:journal/apis/git_migration.dart';
 import 'package:journal/appstate.dart';
-import 'package:journal/datetime_utils.dart';
 import 'package:journal/note.dart';
+import 'package:journal/note_fileName.dart';
 import 'package:journal/storage/git_storage.dart';
 import 'package:journal/storage/notes_repository.dart';
 import 'package:path/path.dart' as p;
@@ -217,7 +217,7 @@ class StateContainerState extends State<StateContainer> {
     Fimber.d("State Container insertNote");
     setState(() {
       if (note.filePath == null || note.filePath.isEmpty) {
-        note.filePath = toIso8601WithTimezone(note.created) + '.md';
+        note.filePath = getFileName(note);
       }
       appState.notes.insert(index, note);
       appState.hasJournalEntries = true;

lib/storage/file_storage.dart

@@ -8,8 +8,6 @@ import 'package:journal/storage/notes_repository.dart';
 import 'package:journal/storage/serializers.dart';
 import 'package:path/path.dart' as p;
 
-typedef String NoteFileNameGenerator(Note note);
-
 /// Each Note is saved in a different file
 /// Each note must have a fileName which ends in a .md
 class FileStorage implements NoteRepository {