Expand a bundle into its components

api_version = "2026-10"

[[extensions]]
name = "Expand a bundle into its components"
handle = "expand-bundle-components"
type = "function"

  [[extensions.targeting]]
  target = "cart.transform.run"
  input_query = "src/cart_transform_run.graphql"
  export = "cart-transform-run"

  [extensions.build]
  command = ""
  path = "dist/function.wasm"

query CartTransformRunInput {
  cart {
    lines {
      id
      merchandise {
        __typename
        ... on ProductVariant {
          componentReference: metafield(namespace: "custom", key: "component_reference") {
            jsonValue
          }
          componentQuantities: metafield(namespace: "custom", key: "component_quantities") {
            jsonValue
          }
        }
      }
    }
  }
}

// @ts-check

/**
 * @typedef {import("../generated/api").CartTransformRunInput} CartTransformRunInput
 * @typedef {import("../generated/api").CartTransformRunResult} CartTransformRunResult
 */

/**
 * The bundle variant lists its components in two variant metafields, the
 * definitions Shopify's bundle guide uses: custom.component_reference (list of
 * variants) and custom.component_quantities (list of integers, same order).
 * Quantities are for one bundle.
 */

/**
 * @param {CartTransformRunInput["cart"]["lines"][number]} line
 * @returns {CartTransformRunResult["operations"][number] | null}
 */
function expandOperation(line) {
  if (line.merchandise.__typename !== "ProductVariant") return null;
  const variantIds = line.merchandise.componentReference?.jsonValue;
  const quantities = line.merchandise.componentQuantities?.jsonValue;
  if (!Array.isArray(variantIds) || variantIds.length === 0) return null;
  // Mismatched lists mean a half-edited bundle; leave the line as it is
  // rather than expand it into the wrong items.
  if (!Array.isArray(quantities) || quantities.length !== variantIds.length) return null;

  // No price on the items: Shopify splits the bundle price across the
  // components by their own prices (its weight price algorithm).
  return {
    lineExpand: {
      cartLineId: line.id,
      expandedCartItems: variantIds.map((merchandiseId, index) => ({ merchandiseId, quantity: quantities[index] })),
    },
  };
}

/**
 * @param {CartTransformRunInput} input
 * @returns {CartTransformRunResult}
 */
export function cartTransformRun(input) {
  const operations = input.cart.lines.map(expandOperation).filter((operation) => operation !== null);
  return { operations };
}