go_intumerables.ex

defmodule GoIntumerables do
  @doc """
  ## Example

  take_into(%Bar{id: 1}, [:id], [])

  # => [id: 1]

  opts = [open: true, secret: "foo", source_id: "2"]
  opts
  |> take_into([:open, :source_id], %{}, fn {k, v} -> {to_string(k), v} end)
  |> URI.encode_query()
  
  # => "?open=true&source_id=2"
  """
  def take_into(source_enum, keys, result, transform \\ & &1)
    when is_enum(source_enum) and is_enum(result) and is_function(transform, 1),
      do: for item <- source_enum, should_take?(item, keys), into: result, do: item |> as_pair() |> transform.()
  
  defguardp is_enum(maybe_enum) when is_list(maybe_enum) or is_map(maybe_enum)

  defp should_take?({k, _}, keys), do: k in keys
  defp should_take?(item, keys) when not is_tuple(item), do: item in keys

  defp as_pair({_, _} = pair), do: pair
  defp as_pair(item) when not is_tuple(item), do: {item, true}
end