Shipping method metadata

[michaelbromley]

Is your feature request related to a problem? Please describe.
It would be useful to allow a ShippingEligibilityChecker & ShippingCalculator to attach arbitrary metadata to their results. For example, with a checker/calculator I am implementing which reads from a CSV price table, it would be useful to be able to include data such as "shipping provider" and "estimated shipping time" in addition to the eligibility & price.

Describe the solution you'd like
Currently the ShippingCalculator.calculate() method returns a ShippingPrice object:

type ShippingPrice = {
    price: number;
    priceWithTax: number;
};

Instead we could return:

type ShippingCalculationResult = {
    price: number;
    priceWithTax: number;
    metadata: Record<string, any>;
};

This could then be return from the eligibleShippingMethods query:

type ShippingMethodQuote {
    id: ID!
    price: Int!
    priceWithTax: Int!
    description: String!
    metadata: JSON
}

Use case

I have a CSV file containing data on a number of couriers (DPD, FedEx, Royal Mail etc) plus data on their charges & delivery times to various countries:

provider     ,country                       ,countryCode,baseWeight,baseCost,incrementWeight,incrementCost,upperWeight,shippingTime
"DPD Classic","Austria"                     ,"AT"       ,"25000"   ,"1376"  ,"25000"        ,"1376"       ,"200000"   ,"4 - 5"
"DPD Classic","Bosnia and Herzegovina"      ,"BA"       ,"25000"   ,"5063"  ,"25000"        ,"2563"       ,"200000"   ,"5 - 7"
"DPD Classic","Belgium"                     ,"BE"       ,"25000"   ,"1088"  ,"25000"        ,"1088"       ,"200000"   ,"3 - 4"

In my ShippingCalculator I take the order weight and shipping address to look up the the prices with eligible couriers.

Currently if I call eligibleShippingMethods from my storefront, I only get a single price. I'd like to additionally be able to display the courier and the expected delivery time too. This could be done with this metadata proposal:

// query 
{
  eligibleShippingMethods {
    id
    price
    description
    metadata
  }
}

// result
[
  {
     "id": "1",
     "price": 1000,
     "description": "Courier Shipping"
     "metadata": {
         "courier": "DPD Classic",
         "deliveryEstimate": "4 - 5"
      }
  }
]

It might also be useful to retain this metadata with the order, as a simple-json field shippingMetadata. For now I will avoid this as I wish to be as conservative as possible when it comes to adding new fields to existing entities.