# typed: true

require 'datadog/tracing/contrib/analytics'
require 'datadog/tracing/contrib/mongodb/ext'
require 'datadog/tracing/contrib/mongodb/parsers'
require 'datadog/tracing/metadata/ext'

module Datadog
  module Tracing
    module Contrib
      module MongoDB
        # `MongoCommandSubscriber` listens to all events from the `Monitoring`
        # system available in the Mongo driver.
        class MongoCommandSubscriber
          def started(event)
            return unless Tracing.enabled?

            service = Datadog.configuration_for(event.address, :service_name) \
                      || Datadog.configuration[:mongo, event.address.seed][:service_name]

            # start a trace and store it in the current thread; using the `operation_id`
            # is safe since it's a unique id used to link events together. Also only one
            # thread is involved in this execution so thread-local storage should be safe. Reference:
            # https://github.com/mongodb/mongo-ruby-driver/blob/master/lib/mongo/monitoring.rb#L70
            # https://github.com/mongodb/mongo-ruby-driver/blob/master/lib/mongo/monitoring/publishable.rb#L38-L56
            span = Tracing.trace(Ext::SPAN_COMMAND, service: service, span_type: Ext::SPAN_TYPE_COMMAND)
            set_span(event, span)

            # build a quantized Query using the Parser module
            query = MongoDB.query_builder(event.command_name, event.database_name, event.command)
            serialized_query = query.to_s

            span.set_tag(Tracing::Metadata::Ext::TAG_COMPONENT, Ext::TAG_COMPONENT)
            span.set_tag(Tracing::Metadata::Ext::TAG_OPERATION, Ext::TAG_OPERATION_COMMAND)

            # Tag as an external peer service
            span.set_tag(Tracing::Metadata::Ext::TAG_PEER_SERVICE, span.service)
            span.set_tag(Tracing::Metadata::Ext::TAG_PEER_HOSTNAME, event.address.host)

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

            # add operation tags; the full query is stored and used as a resource,
            # since it has been quantized and reduced
            span.set_tag(Ext::TAG_DB, query['database'])
            span.set_tag(Ext::TAG_COLLECTION, query['collection'])
            span.set_tag(Ext::TAG_OPERATION, query['operation'])
            span.set_tag(Ext::TAG_QUERY, serialized_query)
            span.set_tag(Tracing::Metadata::Ext::NET::TAG_TARGET_HOST, event.address.host)
            span.set_tag(Tracing::Metadata::Ext::NET::TAG_TARGET_PORT, event.address.port)

            # set the resource with the quantized query
            span.resource = serialized_query
          end

          def failed(event)
            span = get_span(event)
            return unless span

            # the failure is not a real exception because it's handled by
            # the framework itself, so we set only the error and the message
            span.set_error(event)
          rescue StandardError => e
            Datadog.logger.debug("error when handling MongoDB 'failed' event: #{e}")
          ensure
            # whatever happens, the Span must be removed from the local storage and
            # it must be finished to prevent any leak
            span.finish unless span.nil?
            clear_span(event)
          end

          def succeeded(event)
            span = get_span(event)
            return unless span

            # add fields that are available only after executing the query
            rows = event.reply.fetch('n', nil)
            span.set_tag(Ext::TAG_ROWS, rows) unless rows.nil?
          rescue StandardError => e
            Datadog.logger.debug("error when handling MongoDB 'succeeded' event: #{e}")
          ensure
            # whatever happens, the Span must be removed from the local storage and
            # it must be finished to prevent any leak
            span.finish unless span.nil?
            clear_span(event)
          end

          private

          def get_span(event)
            Thread.current[:datadog_mongo_span] \
              && Thread.current[:datadog_mongo_span][event.request_id]
          end

          def set_span(event, span)
            Thread.current[:datadog_mongo_span] ||= {}
            Thread.current[:datadog_mongo_span][event.request_id] = span
          end

          def clear_span(event)
            return if Thread.current[:datadog_mongo_span].nil?

            Thread.current[:datadog_mongo_span].delete(event.request_id)
          end

          def analytics_enabled?
            Contrib::Analytics.enabled?(datadog_configuration[:analytics_enabled])
          end

          def analytics_sample_rate
            datadog_configuration[:analytics_sample_rate]
          end

          def datadog_configuration
            Datadog.configuration[:mongo]
          end
        end
      end
    end
  end
end
