defprotocol RDF.Data do
  @moduledoc """
  An abstraction over the different data structures for collections of RDF statements.
  """

  @doc """
  Deletes statements from a RDF data structure.
  """
  def delete(data, statements)

  @doc """
  Deletes one statement from a RDF data structure and returns a tuple with deleted statement and the changed data structure.
  """
  def pop(data)

  @doc """
  Checks if the given statement exists within a RDF data structure.
  """
  def include?(data, statements)

  @doc """
  Returns the list of all statements of a RDF data structure.
  """
  def statements(data)

  @doc """
  Returns the set of all resources which are subject of the statements of a RDF data structure.
  """
  def subjects(data)

  @doc """
  Returns the set of all properties used within the statements of RDF data structure.
  """
  def predicates(data)

  @doc """
  Returns the  set of all resources used in the objects within the statements of a RDF data structure.
  """
  def objects(data)

  @doc """
  Returns the set of all resources used within the statements of a RDF data structure
  """
  def resources(data)

  @doc """
  Returns the count of all resources which are subject of the statements of a RDF data structure.
  """
  def subject_count(data)

  @doc """
  Returns the count of all statements of a RDF data structure.
  """
  def statement_count(data)

end

defimpl RDF.Data, for: RDF.Description do
  def delete(%RDF.Description{subject: subject} = description,
             %RDF.Description{subject: other_subject})
    when subject != other_subject,
    do: description
  def delete(description, statements), do: RDF.Description.delete(description, statements)
  def pop(description),                do: RDF.Description.pop(description)

  def include?(description, statements),
    do: RDF.Description.include?(description, statements)

  def statements(description), do: RDF.Description.statements(description)
  def predicates(description), do: RDF.Description.predicates(description)
  def objects(description),    do: RDF.Description.objects(description)
  def subjects(%RDF.Description{subject: subject}), do: MapSet.new([subject])

  def resources(%RDF.Description{subject: subject} = description),
    do: RDF.Description.resources(description) |> MapSet.put(subject)

  def subject_count(_),             do: 1
  def statement_count(description), do: RDF.Description.count(description)
end