module OpenTracing
  class Tracer
    # Starts a new span.
    #
    # @param operation_name [String] The operation name for the Span
    #
    # @param child_of [SpanContext, Span] SpanContext that acts as a parent to
    #        the newly-started Span. If a Span instance is provided, its
    #        context is automatically substituted. See [Reference] for more
    #        information.
    #
    #   If specified, the `references` paramater must be omitted.
    #
    # @param references [Array<Reference>] An array of reference
    #   objects that identify one or more parent SpanContexts.
    #
    # @param start_time [Time] When the Span started, if not now
    #
    # @param tags [Hash] Tags to assign to the Span at start time
    #
    # @return [Span] The newly-started Span
    def start_span(operation_name, child_of: nil, references: nil, start_time: Time.now, tags: nil)
      Span::NOOP_INSTANCE
    end

    # Inject a SpanContext into the given carrier
    #
    # @param span_context [SpanContext]
    # @param format [OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK]
    # @param carrier [Carrier] A carrier object of the type dictated by the specified `format`
    def inject(span_context, format, carrier)
      case format
      when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK
        return nil
      else
        warn 'Unknown inject format'
      end
    end

    # Extract a SpanContext in the given format from the given carrier.
    #
    # @param format [OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK]
    # @param carrier [Carrier] A carrier object of the type dictated by the specified `format`
    # @return [SpanContext, nil] the extracted SpanContext or nil if none could be found
    def extract(format, carrier)
      case format
      when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK
        return SpanContext::NOOP_INSTANCE
      else
        warn 'Unknown extract format'
        nil
      end
    end
  end
end