import 'package:intl/intl.dart';

import 'datetime_extension.dart';

/// DateFormat 构造要解析 pattern，列表里高频调用，按 pattern 缓存
final _formatters = <String, DateFormat>{};

DateFormat _formatterOf(String pattern) => _formatters.putIfAbsent(pattern, () => DateFormat(pattern));

/// 可空字符串扩展
extension StringNullableX on String? {
  DateTime? get _localDateTime {
    final value = this?.trim();
    if (value == null || value.isEmpty) return null;
    return DateTime.tryParse(value)?.toLocal();
  }

  String _format(String pattern) {
    final date = _localDateTime;
    return date == null ? '' : _formatterOf(pattern).format(date);
  }

  // ============= utc 字符串 → 各种本地格式 =============

  /// yyyy-MM-dd HH:mm:ss
  String utcToYMDHMS() => _format('yyyy-MM-dd HH:mm:ss');

  /// yyyy-MM-dd HH:mm
  String utcToYMDHM({String gap = '-'}) => _format('yyyy${gap}MM${gap}dd HH:mm');

  /// yyyy-MM-dd
  String utcToYMD({String gap = '-'}) => _format('yyyy${gap}MM${gap}dd');

  /// MM月dd日
  String utcToCnMD() {
    final date = _localDateTime;
    return date == null ? '' : '${date.month}月${date.day}日';
  }

  /// 相对时间："刚刚 / N分钟前 / N小时前 / N天前 / yyyy-MM-dd HH:mm"
  String utcToAgo({String gap = '-'}) {
    final date = _localDateTime;
    //解析不出：本来就是空值兜底“近期”，脏数据给空串
    if (date == null) return this?.trim().isNotEmpty == true ? '' : '近期';

    final diff = DateTime.now().difference(date);
    final s = diff.inSeconds;
    if (s >= 0 && s < 60) return '刚刚';
    final m = diff.inMinutes;
    if (m > 0 && m < 60) return '${m + 1}分钟前';
    final h = diff.inHours;
    if (h > 0 && h < 24) return '${h + 1}小时前';
    final d = diff.inDays;
    if (d > 0 && d < 3) return '${d + 1}天前';
    return date.ymdSMFormat(gap: gap);
  }
}

/// 非空字符串扩展
extension StringX on String {
  /// 截断到最大长度
  String limit(int max) {
    if (max <= 0) return '';
    return length <= max ? this : substring(0, max);
  }

  /// 是否含 16 个以上的 0，用于识别全零设备号（如全零 UUID）
  bool hasManyZeros() {
    const zero = 0x30; //'0'
    var count = 0;
    for (var i = 0; i < length; i++) {
      if (codeUnitAt(i) == zero && ++count >= 16) return true;
    }
    return false;
  }
}