require 'ddtrace/ext/http'
require 'ddtrace/ext/integration'
require 'ddtrace/contrib/analytics'
require 'ddtrace/contrib/grpc/ext'

module Datadog
  module Contrib
    module GRPC
      module DatadogInterceptor
        # The DatadogInterceptor::Server implements the tracing strategy
        # for gRPC server-side endpoints. When the datadog fields have been
        # added to the gRPC call metadata, this middleware component will
        # extract any client-side tracing information, attempting to associate
        # its tracing context with a parent client-side context
        class Server < Base
          def trace(keywords)
            options = {
              span_type: Datadog::Ext::HTTP::TYPE_INBOUND,
              service: service_name,
              resource: format_resource(keywords[:method])
            }
            metadata = keywords[:call].metadata

            set_distributed_context!(tracer, metadata)

            tracer.trace(Ext::SPAN_SERVICE, options) do |span|
              annotate!(span, metadata)

              yield
            end
          end

          private

          def set_distributed_context!(tracer, metadata)
            tracer.provider.context = Datadog::GRPCPropagator
                                      .extract(metadata)
          rescue StandardError => e
            Datadog.logger.debug(
              "unable to propagate GRPC metadata to context: #{e}"
            )
          end

          def annotate!(span, metadata)
            metadata.each do |header, value|
              next if reserved_headers.include?(header)

              span.set_tag(header, value)
            end

            # Tag as an external peer service
            span.set_tag(Datadog::Ext::Integration::TAG_PEER_SERVICE, span.service)

            # Set analytics sample rate
            Contrib::Analytics.set_sample_rate(span, analytics_sample_rate) if analytics_enabled?

            # Measure service stats
            Contrib::Analytics.set_measured(span)
          rescue StandardError => e
            Datadog.logger.debug("GRPC client trace failed: #{e}")
          end

          def reserved_headers
            [Datadog::Ext::DistributedTracing::GRPC_METADATA_TRACE_ID,
             Datadog::Ext::DistributedTracing::GRPC_METADATA_PARENT_ID,
             Datadog::Ext::DistributedTracing::GRPC_METADATA_SAMPLING_PRIORITY]
          end

          def format_resource(proto_method)
            proto_method.owner
                        .to_s
                        .downcase
                        .split('::')
                        .<<(proto_method.name)
                        .join('.')
          end
        end
      end
    end
  end
end