defmodule RDF.NQuads.Decoder do
  @moduledoc false

  use RDF.Serialization.Decoder

  def decode(content, _opts \\ []) do
    with {:ok, tokens, _} <- tokenize(content),
         {:ok, ast}       <- parse(tokens) do
      {:ok, build_dataset(ast)}
    else
      {:error, {error_line, :ntriples_lexer, error_descriptor}, _error_line_again} ->
        {:error, "N-Quad scanner error on line #{error_line}: #{inspect error_descriptor}"}
      {:error, {error_line, :nquads_parser, error_descriptor}} ->
        {:error, "N-Quad parser error on line #{error_line}: #{inspect error_descriptor}"}
    end
  end

  defp tokenize(content), do: content |> to_charlist |> :ntriples_lexer.string

  defp parse(tokens), do: tokens |> :nquads_parser.parse

  defp build_dataset(ast) do
    Enum.reduce ast, RDF.Dataset.new, fn(quad, dataset) ->
      RDF.Dataset.add(dataset, quad)
    end
  end

end