index-shop/assets/js/shopify-cart.js

/**
 * Shopify Storefront API Client
 * Custom implementation using Cart API (2026-01)
 */
class ShopifyCart {
  constructor(config) {
    this.domain = config.domain;
    this.storefrontAccessToken = config.storefrontAccessToken;
    this.apiVersion = '2026-01';
    this.endpoint = `https://${this.domain}/api/${this.apiVersion}/graphql.json`;
    this.cartId = null;
    this.cartItems = [];

    // Load existing cart from localStorage
    this.loadCart();
  }

  /**
   * Make GraphQL request to Shopify Storefront API
   */
  async query(query, variables = {}) {
    const response = await fetch(this.endpoint, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'X-Shopify-Storefront-Access-Token': this.storefrontAccessToken,
      },
      body: JSON.stringify({ query, variables }),
    });

    const result = await response.json();

    if (result.errors) {
      console.error('Shopify API Error:', result.errors);
      throw new Error(result.errors[0].message);
    }

    return result.data;
  }

  /**
   * Get product information by ID
   */
  async getProduct(productId) {
    const query = `
      query getProduct($id: ID!) {
        product(id: $id) {
          id
          title
          description
          availableForSale
          variants(first: 10) {
            edges {
              node {
                id
                title
                price {
                  amount
                  currencyCode
                }
                availableForSale
              }
            }
          }
        }
      }
    `;

    const data = await this.query(query, {
      id: `gid://shopify/Product/${productId}`
    });

    return data.product;
  }

  /**
   * Create a new cart
   */
  async createCart(lines = []) {
    const query = `
      mutation cartCreate($input: CartInput!) {
        cartCreate(input: $input) {
          cart {
            id
            checkoutUrl
            lines(first: 10) {
              edges {
                node {
                  id
                  quantity
                  merchandise {
                    ... on ProductVariant {
                      id
                      title
                      price {
                        amount
                        currencyCode
                      }
                      product {
                        title
                      }
                    }
                  }
                }
              }
            }
          }
          userErrors {
            field
            message
          }
        }
      }
    `;

    const data = await this.query(query, {
      input: { lines }
    });

    if (data.cartCreate.userErrors.length > 0) {
      throw new Error(data.cartCreate.userErrors[0].message);
    }

    this.cartId = data.cartCreate.cart.id;
    this.saveCart();

    return data.cartCreate.cart;
  }

  /**
   * Add item to cart
   */
  async addToCart(variantId, quantity = 1) {
    const lines = [{
      merchandiseId: `gid://shopify/ProductVariant/${variantId}`,
      quantity: quantity
    }];

    let cart;

    if (this.cartId) {
      // Add to existing cart
      const query = `
        mutation cartLinesAdd($cartId: ID!, $lines: [CartLineInput!]!) {
          cartLinesAdd(cartId: $cartId, lines: $lines) {
            cart {
              id
              checkoutUrl
              lines(first: 10) {
                edges {
                  node {
                    id
                    quantity
                    merchandise {
                      ... on ProductVariant {
                        id
                        title
                        price {
                          amount
                          currencyCode
                        }
                        product {
                          title
                        }
                      }
                    }
                  }
                }
              }
            }
            userErrors {
              field
              message
            }
          }
        }
      `;

      const data = await this.query(query, {
        cartId: this.cartId,
        lines
      });

      if (data.cartLinesAdd.userErrors.length > 0) {
        throw new Error(data.cartLinesAdd.userErrors[0].message);
      }

      cart = data.cartLinesAdd.cart;
    } else {
      // Create new cart
      cart = await this.createCart(lines);
    }

    this.cartItems = cart.lines.edges;
    return cart;
  }

  /**
   * Get checkout URL to redirect user
   */
  getCheckoutUrl(cart) {
    return cart?.checkoutUrl || null;
  }

  /**
   * Save cart ID to localStorage
   */
  saveCart() {
    if (this.cartId) {
      localStorage.setItem('shopify_cart_id', this.cartId);
    }
  }

  /**
   * Load cart ID from localStorage
   */
  loadCart() {
    this.cartId = localStorage.getItem('shopify_cart_id');
  }

  /**
   * Clear cart
   */
  clearCart() {
    this.cartId = null;
    this.cartItems = [];
    localStorage.removeItem('shopify_cart_id');
  }
}

// Export for use in other scripts
window.ShopifyCart = ShopifyCart;