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

defimpl RDF.Data, for: RDF.Graph do
  def delete(%RDF.Graph{name: name} = graph, %RDF.Graph{name: other_name})
    when name != other_name,     do: graph
  def delete(graph, statements), do: RDF.Graph.delete(graph, statements)
  def pop(graph),                do: RDF.Graph.pop(graph)

  def include?(graph, statements), do: RDF.Graph.include?(graph, statements)

  def statements(graph), do: RDF.Graph.statements(graph)
  def subjects(graph),   do: RDF.Graph.subjects(graph)
  def predicates(graph), do: RDF.Graph.predicates(graph)
  def objects(graph),    do: RDF.Graph.objects(graph)
  def resources(graph),  do: RDF.Graph.resources(graph)

  def subject_count(graph),   do: RDF.Graph.subject_count(graph)
  def statement_count(graph), do: RDF.Graph.triple_count(graph)
end

defimpl RDF.Data, for: RDF.Dataset do
  def delete(%RDF.Dataset{name: name} = dataset, %RDF.Dataset{name: other_name})
    when name != other_name,       do: dataset
  def delete(dataset, statements), do: RDF.Dataset.delete(dataset, statements)
  def pop(dataset),                do: RDF.Dataset.pop(dataset)

  def include?(dataset, statements), do: RDF.Dataset.include?(dataset, statements)

  def statements(dataset), do: RDF.Dataset.statements(dataset)
  def subjects(dataset),   do: RDF.Dataset.subjects(dataset)
  def predicates(dataset), do: RDF.Dataset.predicates(dataset)
  def objects(dataset),    do: RDF.Dataset.objects(dataset)
  def resources(dataset),  do: RDF.Dataset.resources(dataset)

  def subject_count(dataset),   do: dataset |> subjects |> Enum.count
  def statement_count(dataset), do: RDF.Dataset.statement_count(dataset)
end