import { useEffect, useMemo, useState } from 'react';
import { View, Text, ScrollView } from '@tarojs/components';
import {
  REGION_ALL,
  getCities,
  getCitiesForPicker,
  getDistricts,
  getDistrictsForPicker,
  getProvincesForPicker,
  normalizeRegionSelection,
  toCityLevelRegion,
  type RegionSelection,
} from '../lib/region-data';

type RegionPickerProps = {
  open: boolean;
  value: RegionSelection;
  onClose: () => void;
  onConfirm: (region: RegionSelection) => void;
  levels?: 2 | 3;
};

type PickerLevel = 'province' | 'city' | 'district';

const ALL_TABS: Array<{ key: PickerLevel; label: string }> = [
  { key: 'province', label: '省份' },
  { key: 'city', label: '城市' },
  { key: 'district', label: '区县' },
];

function initialTab(value: RegionSelection, levels: 2 | 3): PickerLevel {
  const normalized = levels === 2 ? toCityLevelRegion(value) : normalizeRegionSelection(value);
  if (levels === 2) {
    return normalized.province && normalized.province !== REGION_ALL ? 'city' : 'province';
  }
  if (normalized.district && normalized.district !== REGION_ALL) return 'district';
  if (normalized.city && normalized.city !== REGION_ALL) return 'city';
  return 'province';
}

function tabLabel(tab: PickerLevel, draft: RegionSelection, fallback: string) {
  if (tab === 'province') {
    return draft.province && draft.province !== REGION_ALL ? draft.province : fallback;
  }
  if (tab === 'city') {
    return draft.city && draft.city !== REGION_ALL ? draft.city : fallback;
  }
  return draft.district && draft.district !== REGION_ALL ? draft.district : fallback;
}

export default function RegionPicker({
  open,
  value,
  onClose,
  onConfirm,
  levels = 3,
}: RegionPickerProps) {
  const [draft, setDraft] = useState<RegionSelection>(value);
  const [activeTab, setActiveTab] = useState<PickerLevel>('province');

  const tabs = levels === 2 ? ALL_TABS.slice(0, 2) : ALL_TABS;

  useEffect(() => {
    if (!open) return;
    const normalized = levels === 2 ? toCityLevelRegion(value) : normalizeRegionSelection(value);
    setDraft(normalized);
    setActiveTab(initialTab(value, levels));
  }, [open, value, levels]);

  const listItems = useMemo(() => {
    if (activeTab === 'province') return getProvincesForPicker();
    if (activeTab === 'city') return getCitiesForPicker(draft.province);
    return getDistrictsForPicker(draft.province, draft.city);
  }, [activeTab, draft.province, draft.city]);

  const selectedValue =
    activeTab === 'province' ? draft.province : activeTab === 'city' ? draft.city : draft.district;

  const canConfirm =
    levels === 2
      ? Boolean(draft.province && draft.city)
      : Boolean(draft.province && draft.city && draft.district);

  if (!open) return null;

  function selectProvince(province: string) {
    if (province === REGION_ALL) {
      setDraft({ province: REGION_ALL, city: REGION_ALL, district: REGION_ALL });
      setActiveTab('city');
      return;
    }
    const nextCities = getCities(province);
    const city = nextCities[0] ?? '';
    if (levels === 2) {
      setDraft({ province, city, district: REGION_ALL });
      setActiveTab('city');
      return;
    }
    const nextDistricts = getDistricts(province, city);
    setDraft({ province, city, district: nextDistricts[0] ?? '' });
    setActiveTab('city');
  }

  function selectCity(city: string) {
    if (city === REGION_ALL) {
      setDraft({ ...draft, city: REGION_ALL, district: REGION_ALL });
      if (levels === 3) setActiveTab('district');
      return;
    }
    if (levels === 2) {
      setDraft({ ...draft, city, district: REGION_ALL });
      return;
    }
    const nextDistricts = getDistricts(draft.province, city);
    setDraft({ ...draft, city, district: nextDistricts[0] ?? '' });
    setActiveTab('district');
  }

  function selectDistrict(district: string) {
    setDraft({ ...draft, district });
  }

  function onSelectItem(item: string) {
    if (activeTab === 'province') selectProvince(item);
    else if (activeTab === 'city') selectCity(item);
    else selectDistrict(item);
  }

  function onTabClick(tab: PickerLevel) {
    if (tab === 'city' && !draft.province) return;
    if (tab === 'district' && (!draft.province || !draft.city)) return;
    setActiveTab(tab);
  }

  function handleConfirm() {
    if (!canConfirm) return;
    const next = levels === 2 ? toCityLevelRegion(draft) : normalizeRegionSelection(draft);
    onConfirm(next);
    onClose();
  }

  return (
    <View className="region-picker-overlay" onClick={onClose}>
      <View className="region-picker-sheet" onClick={(e) => e.stopPropagation()}>
        <View className="region-picker-toolbar">
          <View className="region-picker-tabs">
            {tabs.map((tab) => {
              const disabled =
                (tab.key === 'city' && !draft.province) ||
                (tab.key === 'district' && (!draft.province || !draft.city));
              return (
                <Text
                  key={tab.key}
                  className={`region-picker-tab${activeTab === tab.key ? ' active' : ''}${disabled ? ' disabled' : ''}`}
                  onClick={() => !disabled && onTabClick(tab.key)}
                >
                  {tabLabel(tab.key, draft, tab.label)}
                </Text>
              );
            })}
          </View>
          <Text
            className={`region-picker-confirm${canConfirm ? ' ready' : ''}`}
            onClick={() => canConfirm && handleConfirm()}
          >
            确定
          </Text>
        </View>

        <ScrollView className="region-picker-list" scrollY showScrollbar={false}>
          {listItems.map((item) => (
            <View
              key={item}
              className={`region-picker-option${selectedValue === item ? ' selected' : ''}${
                item === REGION_ALL ? ' region-picker-option--all' : ''
              }`}
              onClick={() => onSelectItem(item)}
            >
              <Text>{item}</Text>
            </View>
          ))}
        </ScrollView>
      </View>
    </View>
  );
}