# encoding: utf-8
# This file is distributed under New Relic's license terms.
# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
require 'new_relic/agent/instrumentation/evented_subscriber'

# Listen for ActiveSupport::Notifications events for ActionView render
# events.  Write metric data and transaction trace segments for each event.
module NewRelic
  module Agent
    module Instrumentation
      class ActionViewSubscriber < EventedSubscriber
        def start(name, id, payload)
          event = RenderEvent.new(name, Time.now, nil, id, payload)
          push_event(event)

          if NewRelic::Agent.is_execution_traced? && event.recordable?
            event.scope = NewRelic::Agent.instance.stats_engine \
              .push_scope(:action_view, event.time)
          end
        end

        def finish(name, id, payload)
          event = pop_event(id)

          if NewRelic::Agent.is_execution_traced? && event.recordable?
            record_metrics(event)
            NewRelic::Agent.instance.stats_engine \
              .pop_scope(event.scope, event.metric_name, event.end)
          end
        end

        def record_metrics(event)
          NewRelic::Agent.instance.stats_engine \
            .record_metrics(event.metric_name,
                            event.duration,
                            :scoped => true)
        end

        class RenderEvent < Event
          # Nearly every "render_blah.action_view" event has a child
          # in the form of "!render_blah.action_view".  The children
          # are the ones we want to record.  There are a couple
          # special cases of events without children.
          def recordable?
            name[0] == '!' ||
              metric_name == 'View/text template/Rendering' ||
              metric_name == 'View/(unknown)/Partial'
          end

          def metric_name
            if parent && (payload[:virtual_path] ||
                          (parent.payload[:identifier] =~ /template$/))
              return parent.metric_name
            elsif payload[:virtual_path]
              identifier = payload[:virtual_path]
            else
              identifier = payload[:identifier]
            end

            # memoize
            @metric_name ||= "View/#{metric_path(identifier)}/#{metric_action(name)}"
            @metric_name
          end

          def metric_path(identifier)
            if identifier == nil
              'file'
            elsif identifier =~ /template$/
              identifier
            elsif (parts = identifier.split('/')).size > 1
              parts[-2..-1].join('/')
            else
              '(unknown)'
            end
          end

          def metric_action(name)
            case name
            when /render_template.action_view$/  then 'Rendering'
            when 'render_partial.action_view'    then 'Partial'
            when 'render_collection.action_view' then 'Partial'
            end
          end
        end
      end
    end
  end
end