module Redlander
  class Stream
    attr_reader :rdf_stream

    def initialize(source)
      @rdf_stream = case source
                    when Statement
                      Redland.librdf_model_find_statements(source.model.rdf_model, source.rdf_statement)
                    when Model
                      Redland.librdf_model_as_stream(source.rdf_model)
                    else
                      # TODO
                      raise NotImplementedError.new
                    end
      raise RedlandError.new("Failed to create a new stream") if @rdf_stream.null?
      ObjectSpace.define_finalizer(self, proc { Redland.librdf_free_stream(@rdf_stream) })
    end

    # End-of-stream?
    def eos?
      Redland.librdf_stream_end(@rdf_stream) != 0
    end

    def succ
      Redland.librdf_stream_next(@rdf_stream).zero?
    end

    def current
      Statement.new(self)
    end

    # Return all the remaining statements in the stream
    # from the current position.
    def tail
      [].tap do |all|
        while !eos?
          all << current
          succ
        end
      end
    end
  end
end