Recursive Flows

defmodule Demo.Inventory.Flows.Search do
  @moduledoc """

  """

  use Ash.Flow, otp_app: :demo

  flow do
    api(Demo.Support)

    argument(:size, :integer)

    argument(:token, :string)

    argument(:query, :struct)

    argument(:check_in, :date) do
      allow_nil? false
    end

    argument(:check_out, :date) do
      allow_nil? false
    end

    argument(:occupancies, {:array, Demo.Inventory.Resources.Types.Occupancy}) do
      allow_nil? false
    end

    returns(:merge_results)
  end

  steps do
    custom :get_hotels, Demo.Inventory.Flows.Steps.GetHotels do
      input(%{
        check_in: arg(:check_in),
        check_out: arg(:check_out),
        occupancies: arg(:occupancies),
        page: [limit: arg(:size), after: arg(:token)]
      })
    end

    custom :filter_unavailable_hotels, Demo.Inventory.Flows.Steps.FilterUnavailableHotels do
      input %{
        hotels: result(:get_hotels)
      }
    end

    custom :need_more_hotels?, Demo.Inventory.Flows.Steps.NeedMoreHotels do
      input %{
        keyset: result(:get_hotels),
        available_hotels: result(:filter_unavailable_hotels),
        needed_size: arg(:size)
      }
    end

    branch :maybe_get_more_hotels, result(:need_more_hotels?) do
      output :get_next_token

      custom :get_next_token, fn %{hotels: hotels}, _ ->
        {:ok, get_in(Map.from_struct(List.last(hotels)), [:__metadata__, :keyset])}
      end do
        input %{
          hotels: result(:filter_unavailable_hotels)
        }
      end

      custom :get_number_of_missing_hotels, fn %{hotels: hotels, size: size}, _ ->
        {:ok, size - length(hotels)}
      end do
        input %{
          hotels: result(:filter_unavailable_hotels),
          size: arg(:size)
        }
      end

      run_flow :get_more_hotels, __MODULE__ do
        input %{
          check_in: arg(:check_in),
          check_out: arg(:check_out),
          occupancies: arg(:occupancies),
          size: result(:get_number_of_missing_hotels),
          token: result(:get_next_token)
        }
      end
    end

    custom :merge_results, Demo.Inventory.Flows.Steps.MergeResults do
      input %{
        hotels: result(:get_hotels),
        more_hotels: result(:maybe_get_more_hotels)
      }
    end
  end
end