/**
 * #38 멀티기관 계정 전환 (feature-screen-dev와 협업)
 * GET  /api/institutions/        — 접근 가능 기관 목록
 * POST /api/auth/switch-tenant   — { tenant_id } → { access_token, tenant_name }
 * 성공: SecureStore 'grd_token' 갱신 + 토스트 + router.replace('/(tabs)')
 */
import { useCallback, useEffect, useState } from 'react'
import {
  View, Text, FlatList, TouchableOpacity, StyleSheet,
  RefreshControl, ActivityIndicator, ToastAndroid, Platform, Alert,
} from 'react-native'
import { useRouter } from 'expo-router'
import * as SecureStore from 'expo-secure-store'
import { COLORS } from '../../constants/Config'
import { getInstitutions, switchTenant } from '../../services/api'
import LineIcon from '../../components/LineIcon'

interface Institution {
  id?: string | number
  inst_id?: string | number
  tenant_id?: string | number
  name?: string
  inst_name?: string
  region?: string
  is_current?: boolean
  current?: boolean
}

function toast(msg: string) {
  if (Platform.OS === 'android') ToastAndroid.show(msg, ToastAndroid.SHORT)
  else Alert.alert('', msg)
}

export default function MultiTenantScreen() {
  const router = useRouter()
  const [items, setItems] = useState<Institution[]>([])
  const [loading, setLoading] = useState(true)
  const [refresh, setRefresh] = useState(false)
  const [switching, setSwitching] = useState<string | number | null>(null)

  const load = useCallback(async (isRefresh = false) => {
    isRefresh ? setRefresh(true) : setLoading(true)
    try {
      const r = await getInstitutions()
      const list: Institution[] = Array.isArray(r.data) ? r.data : r.data?.items ?? []
      setItems(list)
    } catch {
      setItems([])
    } finally {
      setLoading(false)
      setRefresh(false)
    }
  }, [])

  useEffect(() => { load() }, [load])

  const idOf = (inst: Institution) => inst.tenant_id ?? inst.inst_id ?? inst.id

  const handleSwitch = async (inst: Institution) => {
    const tenantId = idOf(inst)
    if (tenantId == null) return
    const name = inst.name ?? inst.inst_name ?? '기관'
    setSwitching(tenantId)
    try {
      const r = await switchTenant(tenantId)
      const { access_token, tenant_name } = r.data ?? {}
      if (access_token) {
        await SecureStore.setItemAsync('grd_token', access_token)
      }
      toast(`${tenant_name ?? name}으로 전환됨`)
      router.replace('/(tabs)')
    } catch (e: any) {
      Alert.alert('전환 실패', e.response?.data?.detail ?? '기관 전환에 실패했습니다.')
    } finally {
      setSwitching(null)
    }
  }

  if (loading) {
    return (
      <View style={s.center}>
        <ActivityIndicator color={COLORS.accent} size="large" />
      </View>
    )
  }

  return (
    <FlatList
      style={{ flex: 1, backgroundColor: COLORS.bg }}
      data={items}
      keyExtractor={(it, i) => String(idOf(it) ?? i)}
      refreshControl={<RefreshControl refreshing={refresh} onRefresh={() => load(true)} tintColor={COLORS.accent} />}
      ListHeaderComponent={
        <View style={s.header}>
          <Text style={s.headerTitle}>기관 전환</Text>
          <Text style={s.headerSub}>접근 가능한 기관 {items.length}곳 · 선택하면 해당 기관으로 전환됩니다</Text>
        </View>
      }
      ListEmptyComponent={
        <View style={s.empty}><Text style={s.emptyText}>접근 가능한 기관이 없습니다.</Text></View>
      }
      contentContainerStyle={items.length === 0 ? { flexGrow: 1 } : undefined}
      renderItem={({ item }) => {
        const isCurrent = item.is_current ?? item.current ?? false
        const tid = idOf(item)
        return (
          <TouchableOpacity
            style={[s.card, isCurrent && s.cardCurrent]}
            disabled={isCurrent || switching != null}
            onPress={() => handleSwitch(item)}
          >
            <View style={s.iconBox}>
              <LineIcon name="building" size={20} color={COLORS.accent} />
            </View>
            <View style={{ flex: 1 }}>
              <Text style={s.name}>{item.name ?? item.inst_name ?? '기관'}</Text>
              {!!item.region && <Text style={s.meta}>{item.region}</Text>}
            </View>
            {isCurrent ? (
              <View style={s.currentBadge}><Text style={s.currentText}>현재</Text></View>
            ) : switching === tid ? (
              <ActivityIndicator size="small" color={COLORS.accent} />
            ) : (
              <Text style={s.chevron}>›</Text>
            )}
          </TouchableOpacity>
        )
      }}
    />
  )
}

const s = StyleSheet.create({
  center: { flex: 1, alignItems: 'center', justifyContent: 'center', backgroundColor: COLORS.bg },
  header: { padding: 20, paddingBottom: 8 },
  headerTitle: { fontSize: 18, fontWeight: '800', color: COLORS.text },
  headerSub: { fontSize: 12, color: COLORS.muted, marginTop: 4 },
  card: {
    flexDirection: 'row', alignItems: 'center', gap: 12,
    backgroundColor: '#fff', marginHorizontal: 16, marginTop: 10,
    borderRadius: 14, padding: 16,
    borderWidth: 1, borderColor: COLORS.border,
  },
  cardCurrent: { borderColor: COLORS.accent, backgroundColor: '#E8F7FB' },
  iconBox: {
    width: 42, height: 42, borderRadius: 11,
    backgroundColor: 'rgba(0,160,200,.08)', alignItems: 'center', justifyContent: 'center',
  },
  name: { fontSize: 15, fontWeight: '700', color: COLORS.text },
  meta: { fontSize: 12, color: COLORS.muted, marginTop: 2 },
  currentBadge: { backgroundColor: COLORS.accent, paddingHorizontal: 10, paddingVertical: 3, borderRadius: 8 },
  currentText: { fontSize: 11, fontWeight: '700', color: '#fff' },
  chevron: { fontSize: 22, color: COLORS.muted },
  empty: { flex: 1, alignItems: 'center', justifyContent: 'center' },
  emptyText: { color: COLORS.muted, fontSize: 14 },
})