import 'package:flutter/material.dart';

import '../data/region_data.dart';

/// 省→市→区三级联动结果。
class RegionResult {
  const RegionResult({
    required this.provinceCode,
    required this.provinceName,
    required this.cityCode,
    required this.cityName,
    required this.districtCode,
    required this.districtName,
  });

  final String provinceCode;
  final String provinceName;
  final String cityCode;
  final String cityName;
  final String districtCode;
  final String districtName;

  /// 拼接展示文本（省名+市名+区名）。
  String get label =>
      '$provinceName$cityName$districtName';
}

/// 省→市→区三级联动底部弹起选择器。
///
/// 数据源统一来自 [RegionData]（已加载的 `province.json`）。
/// 返回 [RegionResult]（含 code 与 name）；用户取消时弹出 null。
class RegionPicker extends StatefulWidget {
  const RegionPicker({
    super.key,
    this.initialProvinceCode,
    this.initialCityCode,
    this.initialDistrictCode,
  });

  final String? initialProvinceCode;
  final String? initialCityCode;
  final String? initialDistrictCode;

  /// 打开选择器底部弹窗，返回所选 [RegionResult] 或 null。
  static Future<RegionResult?> show({
    required BuildContext context,
    String? initialProvinceCode,
    String? initialCityCode,
    String? initialDistrictCode,
  }) {
    return showModalBottomSheet<RegionResult>(
          useSafeArea: true,
      context: context,
      isScrollControlled: true,
      builder: (ctx) => RegionPicker(
        initialProvinceCode: initialProvinceCode,
        initialCityCode: initialCityCode,
        initialDistrictCode: initialDistrictCode,
      ),
    );
  }

  @override
  State<RegionPicker> createState() => _RegionPickerState();
}

class _RegionPickerState extends State<RegionPicker> {
  final RegionData _region = RegionData.instance;

  /// 当前选中层级：0=省 1=市 2=区。
  int _level = 0;
  String? _provinceCode;
  String? _cityCode;
  String? _districtCode;

  @override
  void initState() {
    super.initState();
    _provinceCode = widget.initialProvinceCode;
    _cityCode = widget.initialCityCode;
    _districtCode = widget.initialDistrictCode;
    // 若已带初始省，直接进入市层级以便快速定位。
    if (_provinceCode != null && _provinceCode!.isNotEmpty) {
      _level = 1;
      if (_cityCode != null && _cityCode!.isNotEmpty) {
        _level = 2;
      }
    }
  }

  List<RegionNode> get _currentList {
    switch (_level) {
      case 0:
        return _region.provinces;
      case 1:
        return _region.citiesOf(_provinceCode ?? '');
      case 2:
        return _region.districtsOf(
          _provinceCode ?? '',
          _cityCode ?? '',
        );
      default:
        return const [];
    }
  }

  String _levelTitle() {
    switch (_level) {
      case 0:
        return '选择省份';
      case 1:
        return '选择城市';
      case 2:
        return '选择区县';
      default:
        return '选择地区';
    }
  }

  void _onSelect(RegionNode node) {
    if (_level == 0) {
      setState(() {
        _provinceCode = node.code;
        _cityCode = null;
        _districtCode = null;
        _level = 1;
      });
    } else if (_level == 1) {
      setState(() {
        _cityCode = node.code;
        _districtCode = null;
        _level = 2;
      });
    } else {
      final provinceName = _region.nameOf(_provinceCode ?? '');
      final cityName = _region.nameOf(_cityCode ?? '');
      Navigator.pop(
        context,
        RegionResult(
          provinceCode: _provinceCode ?? '',
          provinceName: provinceName,
          cityCode: _cityCode ?? '',
          cityName: cityName,
          districtCode: node.code,
          districtName: node.name,
        ),
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    final nodes = _currentList;
    return Container(
      height: MediaQuery.of(context).size.height * 0.6,
      padding: const EdgeInsets.only(top: 8),
      child: Column(
        children: [
          Row(
            children: [
              const SizedBox(width: 16),
              Expanded(
                child: Text(
                  _levelTitle(),
                  style: Theme.of(context)
                      .textTheme
                      .titleMedium
                      ?.copyWith(fontWeight: FontWeight.bold),
                ),
              ),
              if (_level > 0)
                TextButton(
                  onPressed: () => setState(() => _level--),
                  child: const Text('上一级'),
                ),
              const SizedBox(width: 8),
            ],
          ),
          const Divider(height: 1),
          Expanded(
            child: ListView.separated(
              itemCount: nodes.length,
              separatorBuilder: (_, __) => const Divider(height: 1),
              itemBuilder: (context, index) {
                final node = nodes[index];
                final isSelected = _isSelected(node);
                return ListTile(
                  title: Text(node.name),
                  trailing: isSelected
                      ? Icon(Icons.check,
                          color: Theme.of(context).colorScheme.primary)
                      : const Icon(Icons.chevron_right),
                  onTap: () => _onSelect(node),
                );
              },
            ),
          ),
        ],
      ),
    );
  }

  bool _isSelected(RegionNode node) {
    if (_level == 0) return node.code == _provinceCode;
    if (_level == 1) return node.code == _cityCode;
    return node.code == _districtCode;
  }
}