parsing of todo, retaining state over multiple sessions.

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])));
+}