defmodule RDF.Serialization.Encoder do
  @moduledoc """
  A behaviour for encoders of `RDF.Graph`s or `RDF.Dataset`s in a specific
  `RDF.Serialization` format.
  """


  @doc """
  Encodes a `RDF.Graph` or `RDF.Dataset`.

  It returns an `{:ok, string}` tuple, with `string` being the serialized
  `RDF.Graph` or `RDF.Dataset`, or `{:error, reason}` if an error occurs.
  """
  @callback encode(RDF.Graph.t | RDF.Dataset.t, keyword) :: keyword(String.t)

  @doc """
  Encodes a `RDF.Graph` or `RDF.Dataset`.

  As opposed to `encode`, it raises an exception if an error occurs.

  Note: The `__using__` macro automatically provides an overridable default
  implementation based on the non-bang `encode` function.
  """
  @callback encode!(RDF.Graph.t | RDF.Dataset.t, keyword) :: String.t


  defmacro __using__(_) do
    quote bind_quoted: [], unquote: true do
      @behaviour unquote(__MODULE__)

      def encode!(data, opts \\ []) do
        case encode(data, opts) do
          {:ok,    data}   -> data
          {:error, reason} -> raise reason
        end
      end

      defoverridable [encode!: 2]
    end
  end

end