import 'package:intl/intl.dart';

/// Affiche une date ISO / parseable en `dd/MM/yyyy`, avec repli sur la chaîne ou [ifEmpty].
String formatIsoDateFr(String? s, {String ifEmpty = '–'}) {
  if (s == null || s.trim().isEmpty) return ifEmpty;
  try {
    return DateFormat('dd/MM/yyyy').format(DateTime.parse(s.trim()));
  } catch (_) {
    return s.trim();
  }
}

/// Parties d'âge calendaire entre [birth] et [reference] (date-only).
({int years, int months, int days}) computeChildAgeParts(
  DateTime birth,
  DateTime reference,
) {
  final birthDay = DateTime(birth.year, birth.month, birth.day);
  final refDay = DateTime(reference.year, reference.month, reference.day);

  var years = refDay.year - birthDay.year;
  var months = refDay.month - birthDay.month;
  var days = refDay.day - birthDay.day;

  if (days < 0) {
    months--;
    final prevMonth = DateTime(refDay.year, refDay.month, 0);
    days += prevMonth.day;
  }
  if (months < 0) {
    years--;
    months += 12;
  }

  return (years: years, months: months, days: days);
}

String _yearLabel(int years) => years == 1 ? '1 an' : '$years ans';

String _monthLabel(int months) => months == 1 ? '1 mois' : '$months mois';

/// Libellé d'âge pour un enfant (liste admin, fiche parent, etc.).
String formatChildAgeLabel({
  String? birthDate,
  String? dueDate,
  String? status,
}) {
  if (status == 'a_naitre') {
    final due = formatIsoDateFr(dueDate, ifEmpty: '');
    if (due.isNotEmpty) return 'Naissance prévue : $due';
    return 'À naître';
  }

  if (birthDate == null || birthDate.trim().isEmpty) return '';

  try {
    final birth = DateTime.parse(birthDate.trim().split('T').first);
    final now = DateTime.now();
    final parts = computeChildAgeParts(birth, now);

    if (parts.years >= 1) {
      if (parts.months > 0) {
        return 'Âge : ${_yearLabel(parts.years)} ${parts.months} mois';
      }
      return 'Âge : ${_yearLabel(parts.years)}';
    }
    if (parts.months >= 1) {
      return 'Âge : ${_monthLabel(parts.months)}';
    }

    final totalDays = DateTime(now.year, now.month, now.day)
        .difference(DateTime(birth.year, birth.month, birth.day))
        .inDays;
    if (totalDays <= 0) return 'Âge : né récemment';
    return 'Âge : $totalDays jour${totalDays > 1 ? 's' : ''}';
  } catch (_) {
    return 'Né le ${formatIsoDateFr(birthDate)}';
  }
}