rdf-ex/lib/rdf/serializations/nquads_encoder.ex

defmodule RDF.NQuads.Encoder do
  @moduledoc false

  use RDF.Serialization.Encoder

  alias RDF.Statement

  @impl RDF.Serialization.Encoder
  @callback encode(RDF.Data.t(), keyword) :: {:ok, String.t()} | {:error, any}
  def encode(data, _opts \\ []) do
    result =
      data
      |> Enum.reduce([], &[statement(&1) | &2])
      |> Enum.reverse()
      |> Enum.join("\n")

    {:ok, if(result == "", do: result, else: "#{result}\n")}
  end

  @spec statement(Statement.t()) :: String.t()
  def statement(statement)

  def statement({subject, predicate, object, nil}) do
    statement({subject, predicate, object})
  end

  def statement({subject, predicate, object, graph}) do
    "#{term(subject)} #{term(predicate)} #{term(object)} #{term(graph)} ."
  end

  def statement({subject, predicate, object}) do
    "#{term(subject)} #{term(predicate)} #{term(object)} ."
  end

  defdelegate term(value), to: RDF.NTriples.Encoder
end