import '../utils/helpers.dart';

/// Sehr vereinfachte österreichische Feiertage (bundesweit).
/// Key = 'YYYY-MM-DD', Value = Name.
Map<String, String> buildHolidayMapAT(int year) {
  final Map<String, String> m = {};

  DateTime easter = _easterSunday(year);
  DateTime easterMon = easter.add(const Duration(days: 1));
  DateTime ascension = easter.add(const Duration(days: 39));
  DateTime whitMon = easter.add(const Duration(days: 50));
  DateTime corpusChristi = easter.add(const Duration(days: 60));

  void add(DateTime d, String name) => m[ymd(d)] = name;

  add(DateTime(year, 1, 1), 'Neujahr');
  add(DateTime(year, 1, 6), 'Heilige Drei Könige');
  add(easterMon, 'Ostermontag');
  add(DateTime(year, 5, 1), 'Staatsfeiertag');
  add(ascension, 'Christi Himmelfahrt');
  add(whitMon, 'Pfingstmontag');
  add(corpusChristi, 'Fronleichnam');
  add(DateTime(year, 8, 15), 'Mariä Himmelfahrt');
  add(DateTime(year, 10, 26), 'Nationalfeiertag');
  add(DateTime(year, 11, 1), 'Allerheiligen');
  add(DateTime(year, 12, 8), 'Mariä Empfängnis');
  add(DateTime(year, 12, 25), 'Christtag');
  add(DateTime(year, 12, 26), 'Stefanitag');

  return m;
}

/// Gaußsche Osterformel (Gregorianisch)
DateTime _easterSunday(int year) {
  final a = year % 19;
  final b = year ~/ 100;
  final c = year % 100;
  final d = b ~/ 4;
  final e = b % 4;
  final f = (b + 8) ~/ 25;
  final g = (b - f + 1) ~/ 3;
  final h = (19 * a + b - d - g + 15) % 30;
  final i = c ~/ 4;
  final k = c % 4;
  final l = (32 + 2 * e + 2 * i - h - k) % 7;
  final m = (a + 11 * h + 22 * l) ~/ 451;
  final month = (h + l - 7 * m + 114) ~/ 31;  // 3=March, 4=April
  final day = ((h + l - 7 * m + 114) % 31) + 1;
  return DateTime(year, month, day);
}