Free shipping on initial orders

query DeliveryInput {
  cart {
    lines {
      sellingPlanAllocation {
        sellingPlan {
          id
        }
      }
      merchandise {
        __typename
      }
    }
    deliveryGroups {
      id
      deliveryOptions {
        handle
      }
    }
  }
}

/**
 * @typedef {import("../generated/api").Input} Input
 * @typedef {import("../generated/api").CartDeliveryOptionsDiscountsGenerateRunResult} CartDeliveryOptionsDiscountsGenerateRunResult
 */

/**
 * cartDeliveryOptionsDiscountsGenerateRun
 *
 * If the cart has at least one line with a selling plan (subscription),
 * apply 100% off shipping (free shipping) to all delivery groups.
 *
 * Mixed carts are allowed: as long as there is at least one subscription line,
 * all delivery options are discounted to free.
 *
 * @param {Input} input
 * @returns {CartDeliveryOptionsDiscountsGenerateRunResult}
 */
export function cartDeliveryOptionsDiscountsGenerateRun(input) {
  const cart = input.cart;

  // No cart or no lines => nothing to do.
  if (!cart || !cart.lines || cart.lines.length === 0) {
    return { operations: [] };
  }

  // 1. Check if there is at least one line with a selling plan allocation.
  const hasSellingPlanLine = cart.lines.some((line) => {
    // We don't need variant details here, just that a selling plan exists.
    return Boolean(line.sellingPlanAllocation);
  });

  // If there are no subscription lines, do not discount shipping.
  if (!hasSellingPlanLine) {
    return { operations: [] };
  }

  // Static message – no metafield/config needed.
  const message = "Free shipping for subscription orders";

  // 2. Build discount candidates for each delivery group.
  const candidates = [];

  if (Array.isArray(cart.deliveryGroups)) {
    for (const group of cart.deliveryGroups) {
      // Ensure we have an ID to target.
      if (!group || !group.id) continue;

      candidates.push({
        // Target the entire group (all its delivery options).
        targets: [
          {
            deliveryGroup: {
              id: group.id
            }
          }
        ],
        message,
        // 100% off shipping => free shipping
        value: {
          percentage: {
            value: 100
          }
        }
      });
    }
  }

  if (candidates.length === 0) {
    return { operations: [] };
  }

  // 3. Wrap candidates in the deliveryDiscountsAdd operation.
  return {
    operations: [
      {
        deliveryDiscountsAdd: {
          candidates,
          // Apply to ALL candidates/groups.
          selectionStrategy: "ALL"
        }
      }
    ]
  };
}