parsing of todo, retaining state over multiple sessions.

lib/addReminder.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:nextcloud_reminder/repeating_task.dart';
+import 'package:nextcloud_reminder/types/tasks.dart';
 
 class AddTaskWidget extends StatefulWidget {
   const AddTaskWidget({super.key, this.restorationId, required this.onSave});
@@ -123,7 +124,7 @@ class _AddTaskWidgetState extends State<AddTaskWidget> with RestorationMixin {
                       const SnackBar(content: Text('Task added.')),
                     );
                     widget.onSave(RepeatingTask(
-                        title: _titleController.text, begin: _beginDate.value, repeat: _repeat,));
+                        task: Task(title: _titleController.text, begin: _beginDate.value), repeat: _repeat,));
                     Navigator.pop(context);
                   }
                 },

lib/homescreen.dart

@@ -1,7 +1,12 @@
+import 'dart:io';
+
 import 'package:flutter/material.dart';
 import 'package:nextcloud_reminder/addReminder.dart';
+import 'package:nextcloud_reminder/parser/todotxt.dart';
 import 'package:nextcloud_reminder/repeating_task.dart';
 import 'package:nextcloud_reminder/table.dart';
+import 'package:nextcloud_reminder/types/tasks.dart';
+import 'package:path_provider/path_provider.dart';
 
 class HomeWidget extends StatefulWidget {
   const HomeWidget({super.key, required this.title});
@@ -21,9 +26,60 @@ class HomeWidget extends StatefulWidget {
   State<HomeWidget> createState() => _HomeWidgetState();
 }
 
-class _HomeWidgetState extends State<HomeWidget> {
+class _HomeWidgetState extends State<HomeWidget> with WidgetsBindingObserver {
+
   final ScrollTable _checkboxes = ScrollTable(title: "TODOs");
   int _counter = 1;
+  late final Directory appDocDirectory;
+  late final File todotxt = File('${appDocDirectory.path}/todo.txt');
+  final List<Task> tasks = [];
+
+  void _loadTodos() {
+    for (var element in tasks) {
+      debugPrint("loaded: ${element.toString()}");
+      _checkboxes.addTask(RepeatingTask(task: element));
+    }
+  }
+
+  void initLazy() async {
+    appDocDirectory = (await getApplicationDocumentsDirectory());
+    if (await todotxt.exists()) {
+      var data = await todotxt.readAsLines();
+      debugPrint(data.toString());
+      tasks.addAll(TodoParser.parse(data));
+      _loadTodos();
+    } else {
+      debugPrint("no todo file found at ${todotxt.path}");
+    }
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+    initLazy();
+  }
+
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    super.dispose();
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state == AppLifecycleState.paused || state == AppLifecycleState.inactive) {
+      // App is in the background, save any unsaved data
+      debugPrint("save to disk");
+      saveData();
+    }
+  }
+  void saveData() async {
+    //TODO: better update lines instead of blindly overwriting.
+    String data = tasks.map((t) => t.toString()).join("\n");
+    debugPrint("Saving:\n$data");
+    await todotxt.writeAsString(data);
+  }
 
   void _addDummyTask() {
     setState(() {
@@ -32,13 +88,14 @@ class _HomeWidgetState extends State<HomeWidget> {
       // so that the display can reflect the updated values. If we changed
       // stuff without calling setState(), then the build method would not be
       // called again, and so nothing would appear to happen.
-      _checkboxes.addTask(RepeatingTask(title: "Dummy Task #$_counter", begin: DateTime.now(), repeat: _counter++));
+      _checkboxes.addTask(RepeatingTask(task: Task(title: "Dummy Task #$_counter", begin: DateTime.now()), repeat: _counter++));
     });
   }
   void _addTask(RepeatingTask? t) {
     if (t != null) {
       setState(() {
         _checkboxes.addTask(t!);
+        tasks.add(t.task);
       });
     }
   }

lib/parser/todotxt.dart

@@ -0,0 +1,79 @@
+import 'package:flutter/material.dart';
+import 'package:petitparser/petitparser.dart';
+import 'package:nextcloud_reminder/types/tasks.dart';
+import 'package:tuple/tuple.dart';
+
+abstract class TodoParser {
+
+  static final _definition = TodoTxtEvaluatorDefinition();
+
+  static final _todoParser = _definition.build();
+
+  static List<Task> parse(List<String> input) {
+    final List<Task> ret = [];
+    for (var element in input) {
+      var parsed = _todoParser.parse(element);
+      if (parsed.isSuccess) {
+        ret.add(parsed.value);
+      } else {
+        debugPrint(parsed.message);
+        debugPrint(element);
+      }
+    }
+    return ret;
+  }
+}
+
+class TodoTxtEvaluatorDefinition extends TodoTxtDefinition {
+
+  @override
+  Parser todoLine() => super.todoLine().map((value) =>
+      //parser gives the following structure:
+      //0: completed? (null | true)
+      //1: priority? (null | uppercase letter)
+      //2: range? (null | [begin-date, (null | end-date)]
+      //3: description: Tuple5<original text, list<projects>, list<contexts>, map<meta>, text without meta>
+      Task( title: value[3].item5,
+            done: value[0] ?? false,
+            priority: value[1],
+            begin: (value[2] == null ? null : value[2][0]),
+            end: (value[2] == null ? null : value[2][1]),
+            projects: value[3].item2,
+            contexts: value[3].item3,
+            meta: value[3].item4,
+          )
+
+  );
+}
+
+class TodoTxtDefinition extends GrammarDefinition {
+
+  Tuple5<String,List<String>,List<String>, Map<String,String>, String> _extract_project_and_context(String input) {
+    final projectPattern = RegExp(r'\+([^ ]+)');
+    final contextPattern = RegExp(r'@([^ ]+)');
+    final metaPattern = RegExp(r'([^ ]+):([^ ]+)');
+    var projects = projectPattern.allMatches(input).map((Match m) => m[1]!);
+    var contexts = contextPattern.allMatches(input).map((Match m) => m[1]!);
+    var meta = metaPattern.allMatches(input).map((Match m) => MapEntry(m[1]!, m[2]!));
+    var cleanInput = input//.replaceAll(projectPattern, '')
+                          //.replaceAll(contextPattern, '')
+                          .replaceAll(metaPattern, '');
+    return Tuple5(input, List.of(projects), List.of(contexts), Map.fromEntries(meta), cleanInput.trim());
+  }
+
+  @override
+  Parser start() => ref0(todoLine).end();
+
+  Parser todoLine() => ref0(completed).trim().optional()
+                     & ref0(priority).trim().optional()
+                     & (ref0(date).trim() & ref0(date).trim().optional()).optional() // completion date + optional creation date
+                     & any().plus().flatten().map(_extract_project_and_context)
+  ;
+
+  Parser completed() => char('x').map((_) => true);
+
+  Parser priority() => (char('(') & pattern('A-Z') & char(')')).map((values) => values[1]);
+
+  Parser date() => (digit().plus().flatten() & char('-') & digit().plus().flatten() & char('-') & digit().plus().flatten())
+                   .map((values) => DateTime(int.parse(values[0]),int.parse(values[2]),int.parse(values[4])));
+}

lib/repeating_task.dart

@@ -1,11 +1,11 @@
 import 'package:flutter/material.dart';
 import 'package:nextcloud_reminder/task_item.dart';
+import 'package:nextcloud_reminder/types/tasks.dart';
 
 class RepeatingTask extends StatefulWidget {
-  const RepeatingTask({super.key, required this.title, required this.begin, this.repeat=1});
+  const RepeatingTask({super.key, required this.task, this.repeat=1});
 
-  final String title;
-  final DateTime begin;
+  final Task task;
   final int repeat;
 
   @override
@@ -14,14 +14,10 @@ class RepeatingTask extends StatefulWidget {
 
 class _RepeatingTaskState extends State<RepeatingTask> {
   late List<TaskItem> _occurrences;
-  late DateTime _first_occurence;
-  late String _title;
 
   @override
   void initState() {
     super.initState();
-    _title = widget.title;
-    _first_occurence = widget.begin;
     _occurrences = List<TaskItem>.generate(10, (index) => TaskItem(done: index % widget.repeat == 0 ? false : null));
   }
 

lib/table.dart

@@ -39,7 +39,7 @@ class _ScrollTableState extends State<ScrollTable> {
           height: 60.0,
           color: Colors.white,
           margin: const EdgeInsets.all(4.0),
-          child: Text(t.title, style: Theme
+          child: Text(t.task.title, style: Theme
               .of(context)
               .textTheme
               .labelMedium),

lib/types/tasks.dart

@@ -0,0 +1,32 @@
+class Task {
+  final bool done;
+  final DateTime? begin;
+  final DateTime? end;
+  final String title;
+  final List<String> contexts;
+  final List<String> projects;
+  final Map<String,String> meta;
+  final String? priority;
+
+  Task({
+    required this.title,
+    this.done = false,
+    this.contexts = const [],
+    this.projects = const [],
+    this.meta = const {},
+    this.priority,
+    this.begin,
+    this.end,
+  });
+
+  @override
+  String toString() {
+    return (done ? "x " : "")
+         + (priority == null ? "" : "(${priority!}) ")
+         + (begin == null ? "" : "${begin!.year}-${begin!.month}-${begin!.day} ")
+         + (end == null ? "" : "${end!.year}-${end!.month}-${end!.day} ")
+         + ("$title ")
+         + meta.entries.map((entry) => "${entry.key}:${entry.value}").join(" ")
+    ;
+  }
+}