# frozen_string_literal: true

module Labkit
  module Tracing
    module Rails
      # ActionViewSubscriber bridges action view notifications to
      # the distributed tracing subsystem
      class ActionViewSubscriber
        include RailsCommon

        COMPONENT_TAG = "ActionView"
        RENDER_TEMPLATE_NOTIFICATION_TOPIC = "render_template.action_view"
        RENDER_COLLECTION_NOTIFICATION_TOPIC = "render_collection.action_view"
        RENDER_PARTIAL_NOTIFICATION_TOPIC = "render_partial.action_view"

        # Instruments Rails ActionView events for opentracing.
        # Returns a lambda, which, when called will unsubscribe from the notifications
        def self.instrument
          subscriber = new

          subscriptions = [
            ActiveSupport::Notifications.subscribe(RENDER_TEMPLATE_NOTIFICATION_TOPIC) do |_, start, finish, _, payload|
              subscriber.notify_render_template(start, finish, payload)
            end,
            ActiveSupport::Notifications.subscribe(RENDER_COLLECTION_NOTIFICATION_TOPIC) do |_, start, finish, _, payload|
              subscriber.notify_render_collection(start, finish, payload)
            end,
            ActiveSupport::Notifications.subscribe(RENDER_PARTIAL_NOTIFICATION_TOPIC) do |_, start, finish, _, payload|
              subscriber.notify_render_partial(start, finish, payload)
            end,
          ]

          create_unsubscriber subscriptions
        end

        # For more information on the payloads: https://guides.rubyonrails.org/active_support_instrumentation.html
        def notify_render_template(start, finish, payload)
          generate_span_for_notification("render_template", start, finish, payload, tags_for_render_template(payload))
        end

        def notify_render_collection(start, finish, payload)
          generate_span_for_notification("render_collection", start, finish, payload, tags_for_render_collection(payload))
        end

        def notify_render_partial(start, finish, payload)
          generate_span_for_notification("render_partial", start, finish, payload, tags_for_render_partial(payload))
        end

        private

        def tags_for_render_template(payload)
          { "component" => COMPONENT_TAG, "template.id" => payload[:identifier], "template.layout" => payload[:layout] }
        end

        def tags_for_render_collection(payload)
          {
            "component" => COMPONENT_TAG,
            "template.id" => payload[:identifier],
            "template.count" => payload[:count] || 0,
            "template.cache.hits" => payload[:cache_hits] || 0,
          }
        end

        def tags_for_render_partial(payload)
          { "component" => COMPONENT_TAG, "template.id" => payload[:identifier] }
        end
      end
    end
  end
end
