discourse/plugins/discourse-presence/plugin.rb

# name: discourse-presence
# about: Show which users are writing a reply to a topic
# version: 1.0
# authors: André Pereira, David Taylor
# url: https://github.com/discourse/discourse-presence.git

enabled_site_setting :presence_enabled

register_asset 'stylesheets/presence.scss'

PLUGIN_NAME ||= "discourse-presence".freeze

after_initialize do

  module ::Presence
    class Engine < ::Rails::Engine
      engine_name PLUGIN_NAME
      isolate_namespace Presence
    end
  end

  module ::Presence::PresenceManager
    def self.get_redis_key(type, id)
      "presence:#{type}:#{id}"
    end

    def self.get_messagebus_channel(type, id)
      "/presence/#{type}/#{id}"
    end

    def self.add(type, id, user_id)
      redis_key = get_redis_key(type, id)
      response = $redis.hset(redis_key, user_id, Time.zone.now)

      response # Will be true if a new key
    end

    def self.remove(type, id, user_id)
      redis_key = get_redis_key(type, id)
      response = $redis.hdel(redis_key, user_id)

      response > 0 # Return true if key was actually deleted
    end

    def self.get_users(type, id)
      redis_key = get_redis_key(type, id)
      user_ids = $redis.hkeys(redis_key).map(&:to_i)

      User.where(id: user_ids)
    end

    def self.publish(type, id)
      topic =
          if type == 'post'
            Post.find_by(id: id).topic
          else
            Topic.find_by(id: id)
          end

      users = get_users(type, id)
      serialized_users = users.map { |u| BasicUserSerializer.new(u, root: false) }
      message = {
        users: serialized_users
      }

      messagebus_channel = get_messagebus_channel(type, id)
      if topic.archetype == Archetype.private_message
        user_ids = User.where('admin or moderator').pluck(:id)
        user_ids += topic.allowed_users.pluck(:id)
        MessageBus.publish(messagebus_channel, message.as_json, user_ids: user_ids)
      else
        MessageBus.publish(messagebus_channel, message.as_json, group_ids: topic.secure_group_ids)
      end

      users
    end

    def self.cleanup(type, id)
      hash = $redis.hgetall(get_redis_key(type, id))
      original_hash_size = hash.length

      any_changes = false

      # Delete entries older than 20 seconds
      hash.each do |user_id, time|
        if Time.zone.now - Time.parse(time) >= 20
          any_changes ||= remove(type, id, user_id)
        end
      end

      any_changes
    end

  end

  require_dependency "application_controller"

  class Presence::PresencesController < ::ApplicationController
    requires_plugin PLUGIN_NAME
    before_action :ensure_logged_in

    def publish
      data = params.permit(
        :response_needed,
        current: [:action, :topic_id, :post_id],
        previous: [:action, :topic_id, :post_id]
      )

      payload = {}

      if data[:previous] && data[:previous][:action].in?(['edit', 'reply'])
        type = data[:previous][:post_id] ? 'post' : 'topic'
        id = data[:previous][:post_id] ? data[:previous][:post_id] : data[:previous][:topic_id]

        topic =
          if type == 'post'
            Post.find_by(id: id)&.topic
          else
            Topic.find_by(id: id)
          end

        if topic
          guardian.ensure_can_see!(topic)

          any_changes = false
          any_changes ||= Presence::PresenceManager.remove(type, id, current_user.id)
          any_changes ||= Presence::PresenceManager.cleanup(type, id)

          users = Presence::PresenceManager.publish(type, id) if any_changes
        end
      end

      if data[:current] && data[:current][:action].in?(['edit', 'reply'])
        type = data[:current][:post_id] ? 'post' : 'topic'
        id = data[:current][:post_id] ? data[:current][:post_id] : data[:current][:topic_id]

        topic =
          if type == 'post'
            Post.find_by(id: id)&.topic
          else
            Topic.find_by(id: id)
          end

        if topic
          guardian.ensure_can_see!(topic)

          any_changes = false
          any_changes ||= Presence::PresenceManager.add(type, id, current_user.id)
          any_changes ||= Presence::PresenceManager.cleanup(type, id)

          users = Presence::PresenceManager.publish(type, id) if any_changes

          if data[:response_needed]
            users ||= Presence::PresenceManager.get_users(type, id)

            serialized_users = users.map { |u| BasicUserSerializer.new(u, root: false) }

            messagebus_channel = Presence::PresenceManager.get_messagebus_channel(type, id)

            payload = {
              messagebus_channel: messagebus_channel,
              messagebus_id: MessageBus.last_id(messagebus_channel),
              users: serialized_users
            }
          end
        end
      end

      render json: payload
    end

  end

  Presence::Engine.routes.draw do
    post '/publish' => 'presences#publish'
  end

  Discourse::Application.routes.append do
    mount ::Presence::Engine, at: '/presence'
  end

end