Elixir map user attributes to meet external service format

map_user_attrs.ex

defmodule UserMapperFunctions do
  def map_my_address(%{
        address: address,
        city: city,
        province: province,
        country: country,
        postalCode: postalCode
      }) do
    "#{address}, #{city}, #{province}, #{country}, #{postalCode}"
  end
end

mappings = %{
  user_name: :login,
  dob: {:date_of_birth, fn value -> Date.from_iso8601!(value) end},
  address: {nil, &UserMapperFunctions.map_my_address/1},
  other_address: {:my_address, %{province: :state, country: :land}}
}

user = %{
  dob: "1990-01-01",
  user_name: "John",
  address: %{
    address: "1st Street",
    city: "Vancouver",
    province: "ON",
    country: "CA",
    postalCode: "999"
  },
  other_address: %{
    address: "1st Street",
    city: "Vancouver",
    province: "ON",
    country: "CA",
    postalCode: "999"
  }
}

defmodule Mapper do
  def map(mappings, map) do
    for {key, new_key} <- mappings, into: %{} do
      {new_key, map_or_op} = get_new_key_and_op(new_key, key) |> IO.inspect()

      if Map.has_key?(map, key), do: transform(map[key], new_key, map_or_op)
    end
  end

  def get_new_key_and_op(new_key, current_key) do
    case new_key do
      {nil, op} when is_function(op) -> {current_key, op}
      {new_key, op} when is_function(op) -> {new_key, op}
      {nil, map} when is_map(map) -> {current_key, map}
      {new_key, map} when is_map(map) -> {new_key, map}
      nil -> {current_key, nil}
      _ -> {new_key, nil}
    end
  end

  defp transform(value, new_key, nil), do: {new_key, value}
  defp transform(value, new_key, op) when is_function(op), do: {new_key, op.(value)}
  defp transform(value, new_key, map) when is_map(map), do: {new_key, map(map, value)}
end

mappings
|> Mapper.map(user)