// Example ApolloClient config showing a Mutation resolver.
const client = new ApolloClient({
  cache: new InMemoryCache(),
  resolvers: {
    Mutation: {
      toggleTodo: (_root, variables, { cache, getCacheKey }) => {
        const id = getCacheKey({ __typename: 'TodoItem', id: variables.id })
        const fragment = gql`
          fragment completeTodo on TodoItem {
            completed
          }
        `;
        const todo = cache.readFragment({ fragment, id });
        const data = { ...todo, completed: !todo.completed };
        cache.writeData({ id, data });
        return null;
      },
    },
  },
});

// Example Apollo Mutation component using the local Mutation resolver.
const TOGGLE_TODO = gql`
  mutation ToggleTodo($id: Int!) {
    toggleTodo(id: $id) @client
  }
`;
const Todo = ({ id, completed, text }) => (
  <Mutation mutation={TOGGLE_TODO} variables={{ id }}>
    {toggleTodo => (
      <li
        onClick={toggleTodo}
        style={{
          textDecoration: completed ? 'line-through' : 'none',
        }}
      >
        {text}
      </li>
    )}
  </Mutation>
);