Keep pre-orders in a separate shipment

api_version = "2026-10"

[[extensions]]
name = "Keep pre-orders in a separate shipment"
handle = "pre-orders-separate-shipment"
type = "function"

  [[extensions.targeting]]
  target = "cart.fulfillment-constraints.generate.run"
  input_query = "src/cart_fulfillment_constraints_generate_run.graphql"
  input_variables = { namespace = "$app", key = "function-configuration" }
  export = "cart-fulfillment-constraints-generate-run"

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

query CartFulfillmentConstraintsGenerateRunInput($preorderTags: [String!]) {
  cart {
    deliverableLines {
      id
      merchandise {
        __typename
        ... on ProductVariant {
          product {
            hasAnyTag(tags: $preorderTags)
          }
        }
      }
    }
  }
  locations {
    id
  }
  fulfillmentConstraintRule {
    metafield(namespace: "$app", key: "function-configuration") {
      jsonValue
    }
  }
}

// @ts-check

/**
 * @typedef {import("../generated/api").CartFulfillmentConstraintsGenerateRunInput} CartFulfillmentConstraintsGenerateRunInput
 * @typedef {import("../generated/api").CartFulfillmentConstraintsGenerateRunResult} CartFulfillmentConstraintsGenerateRunResult
 */

/**
 * Settings stored as JSON in the rule's metafield. `preorderTags` in the same
 * JSON feeds the query variable (see input_variables in the toml), e.g.
 * { "preorderTags": ["pre-order"], "preorderLocationId": "gid://shopify/Location/1234567890" }.
 */
const DEFAULT_CONFIG = {
  // The location that holds (or will receive) pre-order stock.
  preorderLocationId: /** @type {string | null} */ (null),
};

/** @type {CartFulfillmentConstraintsGenerateRunResult} */
const NO_CONSTRAINTS = { operations: [] };

/**
 * @param {CartFulfillmentConstraintsGenerateRunInput} input
 * @returns {CartFulfillmentConstraintsGenerateRunResult}
 */
export function cartFulfillmentConstraintsGenerateRun(input) {
  const config = { ...DEFAULT_CONFIG, ...input.fulfillmentConstraintRule?.metafield?.jsonValue };
  const preorderLocationId = config.preorderLocationId;
  if (!preorderLocationId) return NO_CONSTRAINTS;

  const isPreorder = (/** @type {(typeof input.cart.deliverableLines)[number]} */ line) =>
    line.merchandise.__typename === "ProductVariant" && line.merchandise.product.hasAnyTag;
  const preorderLineIds = input.cart.deliverableLines.filter(isPreorder).map((line) => line.id);
  const inStockLineIds = input.cart.deliverableLines.filter((line) => !isPreorder(line)).map((line) => line.id);
  if (preorderLineIds.length === 0) return NO_CONSTRAINTS;

  const operations = [
    { deliverableLinesMustFulfillFromAdd: { deliverableLineIds: preorderLineIds, locationIds: [preorderLocationId] } },
  ];

  // Keeping the in-stock items away from the pre-order location is what
  // splits the order: they can no longer wait in the same package.
  const otherLocationIds = input.locations.map((location) => location.id).filter((id) => id !== preorderLocationId);
  if (inStockLineIds.length > 0 && otherLocationIds.length > 0) {
    operations.push({
      deliverableLinesMustFulfillFromAdd: { deliverableLineIds: inStockLineIds, locationIds: otherLocationIds },
    });
  }

  return { operations };
}