import React, { useState, useCallback, useMemo, useEffect } from 'react';
import {
  View,
  TouchableOpacity,
  Alert,
  RefreshControl,
  ActivityIndicator,
} from 'react-native';
import { useRouter } from 'expo-router';
import MaterialIcons from '@expo/vector-icons/MaterialIcons';
import {
  AppContainer,
  MyText,
  tw,
  SearchBar,
  MyFlatList,
} from 'common-ui';
import { trpc } from '@/src/trpc-client';
import { formatDistanceToNow } from 'date-fns';

interface User {
  id: number;
  name: string | null;
  mobile: string | null;
  createdAt: string;
  totalOrders: number;
  lastOrderDate: string | null;
}

interface UserItemProps {
  user: User;
  index: number;
  onPress: () => void;
}

const UserItem: React.FC<UserItemProps> = ({ user, index, onPress }) => {
  const displayName = user.name || 'Unnamed User';
  const hasOrders = user.totalOrders > 0;
  
  const lastOrderText = user.lastOrderDate
    ? formatDistanceToNow(new Date(user.lastOrderDate), { addSuffix: true })
    : 'Never';

  return (
    <TouchableOpacity
      onPress={onPress}
      activeOpacity={0.7}
      style={tw`bg-white rounded-xl border border-gray-100 p-4 mb-3 shadow-sm`}
    >
      <View style={tw`flex-row items-center justify-between`}>
        {/* Left: Index number */}
        <View style={tw`w-8 h-8 rounded-full bg-gray-100 items-center justify-center mr-3`}>
          <MyText style={tw`text-gray-600 text-xs font-bold`}>{index + 1}</MyText>
        </View>

        {/* Middle: User Info */}
        <View style={tw`flex-1`}>
          {/* Mobile number - primary identifier */}
          <MyText style={tw`text-gray-900 font-bold text-base mb-0.5`}>
            {user.mobile || 'No Mobile'}
          </MyText>
          
          {/* Name */}
          <MyText style={tw`text-gray-500 text-sm mb-1`}>
            {displayName}
          </MyText>
          
          {/* Registration date */}
          <MyText style={tw`text-gray-400 text-xs`}>
            Registered: {formatDistanceToNow(new Date(user.createdAt), { addSuffix: true })}
          </MyText>
        </View>

        {/* Right: Order Stats */}
        <View style={tw`items-end`}>
          {/* Total Orders */}
          <View style={tw`flex-row items-center mb-1`}>
            <MaterialIcons name="shopping-bag" size={14} color={hasOrders ? '#10B981' : '#9CA3AF'} />
            <MyText style={tw`${hasOrders ? 'text-green-600' : 'text-gray-400'} font-bold text-sm ml-1`}>
              {user.totalOrders} orders
            </MyText>
          </View>
          
          {/* Last Order */}
          <MyText style={tw`text-gray-400 text-xs`}>
            Last: {lastOrderText}
          </MyText>
        </View>
      </View>
    </TouchableOpacity>
  );
};

interface ListHeaderProps {
  searchTerm: string;
  onSearchChange: (text: string) => void;
  userCount: number;
}

const ListHeader: React.FC<ListHeaderProps> = ({ searchTerm, onSearchChange, userCount }) => (
  <View>
    {/* Search Bar */}
    <View style={tw`px-4 py-3 bg-white border-b border-gray-100`}>
      <SearchBar
        value={searchTerm}
        onChangeText={onSearchChange}
        placeholder="Search by mobile number..."
      />
    </View>

    {/* Stats Summary */}
    <View style={tw`px-4 py-2 bg-gray-50`}>
      <MyText style={tw`text-gray-500 text-sm`}>
        Showing {userCount} users
      </MyText>
    </View>
  </View>
);

const ListFooter: React.FC<{ isFetching: boolean }> = ({ isFetching }) => {
  if (!isFetching) return null;
  return (
    <View style={tw`py-4 items-center`}>
      <ActivityIndicator size="small" color="#3b82f6" />
    </View>
  );
};

export default function UserManagement() {
  const router = useRouter();
  const [searchTerm, setSearchTerm] = useState('');
  const [refreshing, setRefreshing] = useState(false);
  const [hasLoadedOnce, setHasLoadedOnce] = useState(false);

  // Infinite scroll query
  const {
    data,
    isLoading,
    isError,
    error,
    fetchNextPage,
    hasNextPage,
    isFetchingNextPage,
    refetch,
  } = trpc.admin.user.getAllUsers.useInfiniteQuery(
    {
      limit: 30,
      search: searchTerm || undefined,
    },
    {
      getNextPageParam: (lastPage) => lastPage.nextCursor,
    }
  );

  useEffect(() => {
    if (data?.pages?.length) {
      setHasLoadedOnce(true);
    }
  }, [data]);

  // Flatten all pages and remove duplicates
  const users = useMemo(() => {
    const allUsers = data?.pages.flatMap((page) => page.users) || [];
    // Remove duplicates based on user id
    const uniqueUsers = allUsers.filter((user, index, self) => 
      index === self.findIndex((u) => u.id === user.id)
    );
    return uniqueUsers;
  }, [data]);

  const handleRefresh = useCallback(async () => {
    setRefreshing(true);
    await refetch();
    setRefreshing(false);
  }, [refetch]);

  const handleLoadMore = useCallback(() => {
    if (hasNextPage && !isFetchingNextPage) {
      fetchNextPage();
    }
  }, [hasNextPage, isFetchingNextPage, fetchNextPage]);

  const handleUserPress = useCallback((userId: number) => {
    router.push(`/(drawer)/user-management/${userId}`);
  }, [router]);

  const renderUserItem = useCallback(({ item, index }: { item: User; index: number }) => {
    return <UserItem user={item} index={index} onPress={() => handleUserPress(item.id)} />;
  }, [handleUserPress]);

  if (isLoading && !hasLoadedOnce) {
    return (
      <AppContainer>
        <View style={tw`flex-1 justify-center items-center`}>
          <ActivityIndicator size="large" color="#3b82f6" />
          <MyText style={tw`text-gray-500 mt-4`}>Loading users...</MyText>
        </View>
      </AppContainer>
    );
  }

  if (isError) {
    return (
      <AppContainer>
        <View style={tw`flex-1 justify-center items-center p-8`}>
          <MaterialIcons name="error-outline" size={64} color="#ef4444" />
          <MyText style={tw`text-gray-900 text-lg font-bold mt-4`}>Error</MyText>
          <MyText style={tw`text-gray-500 mt-2 text-center`}>
            {error?.message || 'Failed to load users'}
          </MyText>
          <TouchableOpacity
            onPress={() => refetch()}
            style={tw`mt-6 bg-blue-600 px-6 py-3 rounded-full`}
          >
            <MyText style={tw`text-white font-semibold`}>Retry</MyText>
          </TouchableOpacity>
        </View>
      </AppContainer>
    );
  }

  return (
      <View style={tw`flex-1 bg-gray-50`}>
        {/* Users List */}
        <MyFlatList
          data={users}
          renderItem={renderUserItem}
          keyExtractor={(item) => item.id.toString()}
          onEndReached={handleLoadMore}
          onEndReachedThreshold={0.5}
          ListHeaderComponent={
            <ListHeader 
              searchTerm={searchTerm} 
              onSearchChange={setSearchTerm} 
              userCount={users.length} 
            />
          }
          ListFooterComponent={<ListFooter isFetching={isFetchingNextPage} />}
          refreshControl={
            <RefreshControl refreshing={refreshing} onRefresh={handleRefresh} />
          }
          contentContainerStyle={tw`pb-8`}
          stickyHeaderIndices={[0]}
          ListEmptyComponent={
            <View style={tw`flex-1 justify-center items-center py-12`}>
              <MaterialIcons name="people-outline" size={64} color="#e5e7eb" />
              <MyText style={tw`text-gray-500 mt-4 text-center text-lg`}>
                No users found
              </MyText>
              {searchTerm && (
                <MyText style={tw`text-gray-400 mt-1 text-center`}>
                  Try adjusting your search
                </MyText>
              )}
            </View>
          }
        />
      </View>
  );
}
