plugin.rb

# name: discourse-hot_topics
# about: Adds ranking to topics
# version: 0.1
# author: Joe Buhlig joebuhlig.com
# url: https://github.com/danskdynamit/discourse-hot-topics

register_asset "stylesheets/upvote.scss"

enabled_site_setting :hot_topics_enabled

Discourse.top_menu_items.push(:hot)
Discourse.anonymous_top_menu_items.push(:hot)
Discourse.filters.push(:hot)
Discourse.anonymous_filters.push(:hot)

after_initialize do
	if SiteSetting.hot_topics_enabled

		require_dependency 'topic'
	    class ::Topic

			def hot_likes
				if SiteSetting.hot_topics_only_op_likes
					self.first_post.like_count
				else
					self.like_count
				end
			end

			def hot_time
				((Time.now - self.created_at) / 1.hour)
			end

			def hot_gravity
				SiteSetting.hot_topics_gravity_rate
			end

			def hot_boost
				SiteSetting.hot_topics_boost_value
			end

			def hot_rating
				(self.hot_likes + self.hot_boost) / ((self.hot_time + 2) ** self.hot_gravity)
			end

			def hot_rating_custom
				self.custom_fields['upvote_hot']
			end

	    end

		require_dependency 'topic_view_serializer'
		class ::TopicViewSerializer
			attributes :hot_likes, :hot_time, :hot_gravity, :hot_boost, :hot_rating

			def hot_likes
				object.topic.hot_likes
			end

			def hot_time
				object.topic.hot_time
			end

			def hot_gravity
				object.topic.hot_gravity
			end

			def hot_boost
				object.topic.hot_boost
			end

			def hot_rating
				object.topic.hot_rating
			end

			def hot_rating_custom
				object.topic.custom_fields['upvote_hot']
			end

		end

		add_to_serializer(:topic_list_item, :hot_time) { object.hot_time }
		add_to_serializer(:topic_list_item, :hot_likes) { object.hot_likes }
		add_to_serializer(:topic_list_item, :hot_gravity) { object.hot_gravity }
		add_to_serializer(:topic_list_item, :hot_boost) { object.hot_boost }
		add_to_serializer(:topic_list_item, :hot_rating_custom) { object.hot_rating_custom }

		require_dependency 'topic_query'
		class ::TopicQuery
			SORTABLE_MAPPING["hot"] = "custom_fields.upvote_hot"

		  def list_hot
		  	topics = create_list(:hot, {order: "hot"})
		  end

		end

		module ::Jobs

      class HotRating < Jobs::Scheduled
        every SiteSetting.hot_topics_calc_period.minutes

        def execute(args)
          Topic.where(closed: false, archetype: 'regular').find_each do |topic|
            topic.custom_fields['upvote_hot'] = (topic.hot_rating * 1000000000).to_i
            topic.save
          end
        end
      end

    end

    TopicList.preloaded_custom_fields << "upvote_hot" if TopicList.respond_to? :preloaded_custom_fields

	end
end