import { Component } from 'react';
import { Mutation } from 'react-apollo';
import PropTypes from 'prop-types';
import gql from 'graphql-tag';
import User, { CURRENT_USER_QUERY } from './User';

const ADD_TO_CART_MUTATION = gql`
  mutation addToCart($id: ID!) {
    addToCart(id: $id) {
      id
      quantity
      item {
        id
        price
        description
        image
        title
      }
    }
  }
`;

class AddToCart extends Component {
  static propTypes = {
    id: PropTypes.string.isRequired,
  };

  update = (cache, payload) => {
    const newCartItem = payload.data.addToCart;
    const data = cache.readQuery({ query: CURRENT_USER_QUERY });

    const existingIndex = data.me.cart.findIndex(cartItem => cartItem.id === newCartItem.id);
    if (existingIndex >= 0) {
      // already in cache, just replace it
      data.me.cart = [
        ...data.me.cart.slice(0, existingIndex),
        newCartItem,
        ...data.me.cart.slice(existingIndex + 1),
      ];
    } else {
      data.me.cart = [...data.me.cart, newCartItem];
    }
    cache.writeQuery({ query: CURRENT_USER_QUERY, data });
  };

  render() {
    const { id } = this.props;
    return (
      <User>
        {({ data: { me }, loading }) => {
          if (!me || loading) return null;
          return (
            <Mutation mutation={ADD_TO_CART_MUTATION} variables={{ id }} update={this.update}>
              {(addToCart, { loading }) => (
                <button disabled={loading} onClick={addToCart}>
                  🛒 Add{loading && 'ing'} To Cart
                </button>
              )}
            </Mutation>
          );
        }}
      </User>
    );
  }
}

export default AddToCart;
export { ADD_TO_CART_MUTATION };