resource_cases.ex

defmodule Api.Resource.Cases do
  defmacro __using__([type: type]) do
    [read, create] = Utils.resources(type, [Read, Create])
    service = Utils.service(type)

    quote do
      use PoeApi.Resource

      let cases = unquote(service).get_all(Input.get)

      hyper do
        action do
          %{
            "count" => length(cases),
            "collection" => for item <- cases do
              link_to(unquote(read), item: item["sys_id"])
              |> ^Map.merge(item)
            end,
            "create" => link_to(unquote(create))
          }
        end
      end
    end
  end
end

defmodule Api.Resource.ChangeRequests, do: use Api.Resource.Cases, type: "change_requests"
defmodule Api.Resource.ServiceRequests, do: use Api.Resource.Cases, type: "service_requests"
defmodule Api.Resource.Incidents, do: use Api.Resource.Cases, type: "incidents"

services_case.ex

defmodule Case do
  defmacro __using__([type: typename]) do
    case_schemaname = String.rstrip(typename, ?s)
    case_typename = Mix.Utils.camelize(String.rstrip(typename, ?s))
    case_service = Module.concat([Api.Service.Now, case_typename])

    quote do
      import unquote(__MODULE__)
      use Api.Model

      schema unquote(case_schemaname) do
        field :description, :string
        field :number,      :string
      end

      def get(id, input) do
        unquote(case_service).get_one(id, input)
      end

      def get_all(input) do
        unquote(case_service).get_all(input)
      end

      def create(body) do
        unquote(case_service).create(body)
      end

      def remove(id) do
        unquote(case_service).remove(id)
      end

      @create_inputs ~w(
        description
        update
      )
    end
  end
end

defmodule Api.Service.ChangeRequest, do: use Case, type: "change_requests"
defmodule Api.Service.ServiceRequest, do: use Case, type: "service_requests"
defmodule Api.Service.Incident, do: use Case, type: "incidents"