import 'package:commons_core/commons_core.dart';
import 'package:intl/intl.dart';

/// One row of the rendered chat: either a day separator or a message. Pure data
/// so the grouping can be unit-tested without widgets.
sealed class ChatTimelineItem {
  const ChatTimelineItem();
}

/// A "— Today —" style divider before the first message of a calendar day.
class ChatDaySeparator extends ChatTimelineItem {
  const ChatDaySeparator(this.day);

  /// Local midnight of the day this divider introduces.
  final DateTime day;
}

/// A chat bubble.
class ChatMessageRow extends ChatTimelineItem {
  const ChatMessageRow(this.message);

  final PrivateMessage message;
}

/// Groups [messages] (oldest first) into a timeline, inserting a
/// [ChatDaySeparator] before the first message of each local calendar day.
/// Result stays oldest-first.
List<ChatTimelineItem> chatTimeline(List<PrivateMessage> messages) {
  final out = <ChatTimelineItem>[];
  DateTime? lastDay;
  for (final m in messages) {
    final day = DateTime(m.at.year, m.at.month, m.at.day);
    if (lastDay == null || day != lastDay) {
      out.add(ChatDaySeparator(day));
      lastDay = day;
    }
    out.add(ChatMessageRow(m));
  }
  return out;
}

/// The human label for a day separator: "Today"/"Yesterday" for the two most
/// recent days (localized by the caller), otherwise a locale-formatted date
/// (weekday + day + month, plus year when it differs from [now]).
///
/// [localeCode] must be an `intl`-known locale — pass the *Localizations* locale
/// (which maps Asturian → Spanish), never the raw app locale, since `ast` has no
/// `intl` date symbols and would throw. Mirrors backup_section.dart.
String chatDayLabel(
  DateTime day, {
  required DateTime now,
  required String today,
  required String yesterday,
  required String localeCode,
}) {
  final startOfToday = DateTime(now.year, now.month, now.day);
  final startOfDay = DateTime(day.year, day.month, day.day);
  final diffDays = startOfToday.difference(startOfDay).inDays;
  if (diffDays == 0) return today;
  if (diffDays == 1) return yesterday;
  final format = day.year == now.year
      ? DateFormat.MMMMEEEEd(localeCode)
      : DateFormat.yMMMMEEEEd(localeCode);
  return format.format(day);
}

/// The clock time shown on a bubble, in the locale's own 12/24-hour convention.
/// See [chatDayLabel] for the [localeCode] caveat.
String chatBubbleTime(DateTime at, String localeCode) =>
    DateFormat.jm(localeCode).format(at);