import 'package:intl/intl.dart';
import 'package:timezone/timezone.dart' as tz;

// Source - https://stackoverflow.com/a/54775297
// Posted by diegoveloper, modified by community. See post 'Timeline' for change history
// Retrieved 2026-05-09, License - CC BY-SA 4.0

String _printDuration(Duration duration) {
  String negativeSign = duration.isNegative ? '-' : '';
  String twoDigits(int n) => n.toString().padLeft(2, "0");
  String twoDigitMinutes = twoDigits(duration.inMinutes.abs());
  String twoDigitSeconds = twoDigits(duration.inSeconds.remainder(60).abs());
  return "$negativeSign$twoDigitMinutes:$twoDigitSeconds";
}

String formatTimeWindow(String? starts, String? ends) {
  if (starts != null && ends != null) {
    DateTime? startDt = _tryParseServerDateTime(starts);
    DateTime? endDt = _tryParseServerDateTime(ends);
    if (startDt == null || endDt == null) {
      return '--:--';
    }

    Duration songLength = endDt.difference(startDt);

    return _printDuration(songLength);
  }

  return "--:--";
}

String formatStartingTime(String? startingTime, {String? sourceTimezone}) {
  if (startingTime != null) {
    final DateTime? localStart = _serverTimeToLocal(
      startingTime,
      sourceTimezone: sourceTimezone,
    );
    if (localStart == null) {
      return '--:--';
    }
    return DateFormat('jm').format(localStart);
  }
  return "--:--";
}

DateTime? _serverTimeToLocal(String rawTime, {String? sourceTimezone}) {
  final DateTime? parsed = _tryParseServerDateTime(rawTime);
  if (parsed == null) {
    return null;
  }

  if (_hasExplicitTimezone(rawTime)) {
    return parsed.toLocal();
  }

  // API timestamps are wall-clock values in the API timezone field.
  if (sourceTimezone == null || sourceTimezone.trim().isEmpty) {
    return parsed;
  }

  try {
    final tz.Location sourceLocation = tz.getLocation(sourceTimezone.trim());
    final tz.TZDateTime sourceTime = tz.TZDateTime(
      sourceLocation,
      parsed.year,
      parsed.month,
      parsed.day,
      parsed.hour,
      parsed.minute,
      parsed.second,
      parsed.millisecond,
      parsed.microsecond,
    );
    return DateTime.fromMillisecondsSinceEpoch(
      sourceTime.millisecondsSinceEpoch,
      isUtc: true,
    ).toLocal();
  } catch (_) {
    return parsed;
  }
}

bool _hasExplicitTimezone(String value) {
  final String trimmed = value.trim();

  if (trimmed.endsWith('Z') || trimmed.endsWith('z')) {
    return true;
  }

  final RegExp offsetPattern = RegExp(r'[+-]\d{2}:?\d{2}$');
  return offsetPattern.hasMatch(trimmed);
}

DateTime? _tryParseServerDateTime(String value) {
  final String trimmed = value.trim();
  if (trimmed.isEmpty) {
    return null;
  }

  final DateTime? isoAttempt = DateTime.tryParse(trimmed);
  if (isoAttempt != null) {
    return isoAttempt;
  }

  final RegExp serverDateTimePattern = RegExp(
    r'^(\d{4})-(\d{2})-(\d{2})\s+(\d{2}):(\d{2}):(\d{2})(?:\.(\d{1,6}))?$',
  );
  final RegExpMatch? match = serverDateTimePattern.firstMatch(trimmed);
  if (match == null) {
    return null;
  }

  int parsePart(int group) => int.parse(match.group(group)!);

  final int year = parsePart(1);
  final int month = parsePart(2);
  final int day = parsePart(3);
  final int hour = parsePart(4);
  final int minute = parsePart(5);
  final int second = parsePart(6);

  final String fraction = (match.group(7) ?? '').padRight(6, '0');
  final int microseconds =
      fraction.isEmpty ? 0 : int.parse(fraction.substring(0, 6));

  return DateTime(
    year,
    month,
    day,
    hour,
    minute,
    second,
    microseconds ~/ 1000,
    microseconds % 1000,
  );
}