todotxt_reminder/lib/parser/todotxt.dart

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<TaskExtra> parse(List<String> input) {
    final List<TaskExtra> ret = [];
    var line=1;
    for (var element in input) {
      var parsed = _todoParser.parse(element);
      if (parsed.isSuccess) {
        ret.add(TaskExtra.fromTask(parsed.value, lineNumber: line));
      } else {
        debugPrint(parsed.message);
        debugPrint(element);
      }
      line++;
    }
    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])));
}