const _weekdays = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
const _months = [
  'Jan',
  'Feb',
  'Mar',
  'Apr',
  'May',
  'Jun',
  'Jul',
  'Aug',
  'Sep',
  'Oct',
  'Nov',
  'Dec',
];
const _monthsLong = [
  'January',
  'February',
  'March',
  'April',
  'May',
  'June',
  'July',
  'August',
  'September',
  'October',
  'November',
  'December',
];

String inr(int n) {
  final neg = n < 0;
  final s = n.abs().toString();
  if (s.length <= 3) return '${neg ? '-' : ''}$s';
  final last = s.substring(s.length - 3);
  var rest = s.substring(0, s.length - 3);
  final parts = <String>[];
  while (rest.length > 2) {
    parts.insert(0, rest.substring(rest.length - 2));
    rest = rest.substring(0, rest.length - 2);
  }
  if (rest.isNotEmpty) parts.insert(0, rest);
  return '${neg ? '-' : ''}${parts.join(',')},$last';
}

String rupees(int n) => '₹${inr(n)}';

DateTime dateOnly(DateTime d) => DateTime(d.year, d.month, d.day);
bool sameDay(DateTime a, DateTime b) =>
    a.year == b.year && a.month == b.month && a.day == b.day;
DateTime addDays(DateTime d, int n) => DateTime(d.year, d.month, d.day + n);

/// Fri, 16 Oct 2026
String dateLong(DateTime d) =>
    '${_weekdays[d.weekday - 1]}, ${d.day} ${_months[d.month - 1]} ${d.year}';

/// Fri, 16 Oct
String dateShort(DateTime d) =>
    '${_weekdays[d.weekday - 1]}, ${d.day} ${_months[d.month - 1]}';

/// October 2026
String monthYear(DateTime d) => '${_monthsLong[d.month - 1]} ${d.year}';

/// 12:41 PM
String time12(DateTime d) {
  final h = d.hour % 12 == 0 ? 12 : d.hour % 12;
  final m = d.minute.toString().padLeft(2, '0');
  return '$h:$m ${d.hour >= 12 ? 'PM' : 'AM'}';
}

String isoDate(DateTime d) =>
    '${d.year.toString().padLeft(4, '0')}-${d.month.toString().padLeft(2, '0')}-${d.day.toString().padLeft(2, '0')}';

String plural(int n, String one, [String? many]) =>
    '${inr(n)} ${n == 1 ? one : (many ?? '${one}s')}';

/// 919000012345 -> +91 90000 12345
String fmtPhone(String? digits) {
  if (digits == null || digits.isEmpty) return '';
  if (digits.length == 12 && digits.startsWith('91')) {
    return '+91 ${digits.substring(2, 7)} ${digits.substring(7)}';
  }
  return '+$digits';
}

String initials(String name) {
  final parts = name.split(RegExp(r'[._\- ]+')).where((p) => p.isNotEmpty);
  final list = parts.toList();
  if (list.isEmpty) return '?';
  if (list.length == 1) {
    final w = list.first;
    return w.substring(0, w.length >= 2 ? 2 : 1).toUpperCase();
  }
  return (list[0][0] + list[1][0]).toUpperCase();
}

String tierLabel(int tier) => '${tier}th prize';

/// "5th prize", or "5th + 8th prize" for an ending in two tiers.
String tiersLabel(List<int> tiers) {
  final sorted = [...tiers]..sort();
  if (sorted.length < 2) return sorted.isEmpty ? '' : tierLabel(sorted.first);
  return '${sorted.map((t) => '${t}th').join(' + ')} prize';
}

/// A server instant (UTC) as the Indian wall-clock time the screens show.
DateTime istWallClock(DateTime instant) {
  final t = instant.toUtc().add(const Duration(hours: 5, minutes: 30));
  return DateTime(t.year, t.month, t.day, t.hour, t.minute, t.second);
}

/// Parses a YYYY-MM-DD calendar date.
DateTime parseDate(String iso) => DateTime(
  int.parse(iso.substring(0, 4)),
  int.parse(iso.substring(5, 7)),
  int.parse(iso.substring(8, 10)),
);