// apollo/client.ts
import { ApolloClient, InMemoryCache, createHttpLink, split } from '@apollo/client';
import { GraphQLWsLink } from '@apollo/client/link/subscriptions';
import { getMainDefinition } from '@apollo/client/utilities';
import { setContext } from '@apollo/client/link/context';
import { createClient } from 'graphql-ws';
import AsyncStorage from '@react-native-async-storage/async-storage';
import { AsyncStorageWrapper, CachePersistor } from 'apollo3-cache-persist';

const httpLink = createHttpLink({
  uri: 'https://api.example.com/graphql',
});

const wsLink = new GraphQLWsLink(
  createClient({
    url: 'wss://api.example.com/graphql',
    connectionParams: async () => {
      const token = await AsyncStorage.getItem('authToken');
      return { authorization: token ? `Bearer ${token}` : '' };
    },
  })
);

const authLink = setContext(async (_, { headers }) => {
  const token = await AsyncStorage.getItem('authToken');
  return {
    headers: {
      ...headers,
      authorization: token ? `Bearer ${token}` : '',
    },
  };
});

const splitLink = split(
  ({ query }) => {
    const definition = getMainDefinition(query);
    return definition.kind === 'OperationDefinition' && definition.operation === 'subscription';
  },
  wsLink,
  authLink.concat(httpLink)
);

const cache = new InMemoryCache({
  typePolicies: {
    Query: {
      fields: {
        posts: {
          keyArgs: false,
          merge(existing = [], incoming) {
            return [...existing, ...incoming];
          },
        },
      },
    },
  },
});

export const persistor = new CachePersistor({
  cache,
  storage: new AsyncStorageWrapper(AsyncStorage),
});

export const client = new ApolloClient({
  link: splitLink,
  cache,
  defaultOptions: {
    watchQuery: {
      fetchPolicy: 'cache-and-network',
    },
  },
});

# codegen.yml
schema: https://api.example.com/graphql
documents: 'src/**/*.graphql'
generates:
  src/generated/graphql.ts:
    plugins:
      - typescript
      - typescript-operations
      - typescript-react-apollo
    config:
      withHooks: true
      withComponent: false
      withHOC: false
      skipTypename: false
      dedupeFragments: true

// features/posts/hooks/usePosts.ts
import { usePostsQuery, useCreatePostMutation } from '../../../generated/graphql';

export function usePosts() {
  const { data, loading, error, refetch, fetchMore } = usePostsQuery({
    variables: { first: 10 },
    notifyOnNetworkStatusChange: true,
  });

  const [createPost] = useCreatePostMutation({
    update(cache, { data }) {
      cache.modify({
        fields: {
          posts(existingPosts = []) {
            const newPostRef = cache.writeFragment({
              data: data?.createPost,
              fragment: PostFragmentDoc,
            });
            return [newPostRef, ...existingPosts];
          },
        },
      });
    },
    optimisticResponse: (variables) => ({
      __typename: 'Mutation',
      createPost: {
        __typename: 'Post',
        id: 'temp-id',
        title: variables.title,
        body: variables.body,
        createdAt: new Date().toISOString(),
      },
    }),
  });

  const loadMore = () => {
    if (data?.posts.pageInfo.hasNextPage) {
      fetchMore({
        variables: {
          after: data.posts.pageInfo.endCursor,
        },
      });
    }
  };

  return {
    posts: data?.posts.edges.map((e) => e.node) ?? [],
    loading,
    error,
    refetch,
    loadMore,
    createPost,
  };
}

// Apollo/Network.swift
import Apollo
import ApolloWebSocket

class Network {
    static let shared = Network()

    private(set) lazy var apollo: ApolloClient = {
        let store = ApolloStore(cache: InMemoryNormalizedCache())

        let provider = DefaultInterceptorProvider(store: store)
        let url = URL(string: "https://api.example.com/graphql")!

        let transport = RequestChainNetworkTransport(
            interceptorProvider: provider,
            endpointURL: url
        )

        return ApolloClient(networkTransport: transport, store: store)
    }()
}