discourse/lib/topic_view.rb

# frozen_string_literal: true

class TopicView
  MEGA_TOPIC_POSTS_COUNT = 10000
  MIN_POST_READ_TIME = 4.0

  def self.on_preload(&blk)
    (@preload ||= Set.new) << blk
  end

  def self.cancel_preload(&blk)
    if @preload
      @preload.delete blk
      if @preload.length == 0
        @preload = nil
      end
    end
  end

  def self.preload(topic_view)
    if @preload
      @preload.each { |preload| preload.call(topic_view) }
    end
  end

  attr_reader(
    :topic,
    :posts,
    :guardian,
    :filtered_posts,
    :chunk_size,
    :print,
    :message_bus_last_id,
    :queued_posts_enabled,
    :personal_message,
    :can_review_topic,
    :page
  )
  alias queued_posts_enabled? queued_posts_enabled

  attr_accessor(
    :draft,
    :draft_key,
    :draft_sequence,
    :user_custom_fields,
    :post_custom_fields,
    :post_number
  )

  delegate :category, to: :topic, allow_nil: true, private: true
  delegate :require_reply_approval?, to: :category, prefix: true, allow_nil: true, private: true

  def self.print_chunk_size
    1000
  end

  def self.chunk_size
    20
  end

  def self.default_post_custom_fields
    @default_post_custom_fields ||= [Post::NOTICE, "action_code_who", "action_code_path"]
  end

  def self.post_custom_fields_allowlisters
    @post_custom_fields_allowlisters ||= Set.new
  end

  def self.add_post_custom_fields_allowlister(&block)
    post_custom_fields_allowlisters << block
  end

  def self.allowed_post_custom_fields(user, topic)
    wpcf = default_post_custom_fields + post_custom_fields_allowlisters.map { |w| w.call(user, topic) }
    wpcf.flatten.uniq
  end

  def self.add_custom_filter(key, &blk)
    @custom_filters ||= {}
    @custom_filters[key] = blk
  end

  def self.custom_filters
    @custom_filters || {}
  end

  # Configure a default scope to be applied to @filtered_posts.
  # The registered block is called with @filtered_posts and an instance of
  # `TopicView`.
  #
  # This API should be considered experimental until it is exposed in
  # `Plugin::Instance`.
  def self.apply_custom_default_scope(&block)
    custom_default_scopes << block
  end

  def self.custom_default_scopes
    @custom_default_scopes ||= []
  end

  # For testing
  def self.reset_custom_default_scopes
    @custom_default_scopes = nil
  end

  def initialize(topic_or_topic_id, user = nil, options = {})
    @topic = find_topic(topic_or_topic_id)
    @user = user
    @guardian = Guardian.new(@user)

    check_and_raise_exceptions(options[:skip_staff_action])

    @message_bus_last_id = MessageBus.last_id("/topic/#{@topic.id}")

    options.each do |key, value|
      self.instance_variable_set("@#{key}".to_sym, value)
    end

    @post_number = [@post_number.to_i, 1].max

    @include_suggested = options.fetch(:include_suggested) { true }
    @include_related = options.fetch(:include_related) { true }

    @chunk_size =
      case
      when @print then TopicView.print_chunk_size
      else TopicView.chunk_size
      end

    @limit ||= @chunk_size

    @page = @page.to_i > 1 ? @page.to_i : calculate_page

    setup_filtered_posts
    @filtered_posts = apply_default_scope(@filtered_posts)
    filter_posts(options)

    if @posts && !@skip_custom_fields
      if (added_fields = User.allowed_user_custom_fields(@guardian)).present?
        @user_custom_fields = User.custom_fields_for_ids(@posts.pluck(:user_id), added_fields)
      end

      if (allowed_fields = TopicView.allowed_post_custom_fields(@user, @topic)).present?
        @post_custom_fields = Post.custom_fields_for_ids(@posts.pluck(:id), allowed_fields)
      end
    end

    TopicView.preload(self)

    @draft_key = @topic.draft_key
    @draft_sequence = DraftSequence.current(@user, @draft_key)

    @can_review_topic = @guardian.can_review_topic?(@topic)
    @queued_posts_enabled = NewPostManager.queue_enabled? || category_require_reply_approval?
    @personal_message = @topic.private_message?
  end

  def show_read_indicator?
    return false if !@user || !topic.private_message?

    topic.allowed_groups.any? do |group|
      group.publish_read_state? && group.users.include?(@user)
    end
  end

  def canonical_path
    if SiteSetting.embed_set_canonical_url
      topic_embed = topic.topic_embed
      return topic_embed.embed_url if topic_embed
    end
    path = relative_url.dup
    path << ((@page > 1) ? "?page=#{@page}" : "")
    path
  end

  def contains_gaps?
    @contains_gaps
  end

  def gaps
    return unless @contains_gaps

    @gaps ||= begin
      if is_mega_topic?
        nil
      else
        Gaps.new(filtered_post_ids, apply_default_scope(unfiltered_posts).pluck(:id))
      end
    end
  end

  def last_post
    return nil if @posts.blank?
    @last_post ||= @posts.last
  end

  def prev_page
    @page > 1 && posts.size > 0 ? @page - 1 : nil
  end

  def next_page
    @next_page ||= begin
      if last_post && highest_post_number && (highest_post_number > last_post.post_number)
        @page + 1
      end
    end
  end

  def prev_page_path
    if prev_page > 1
      "#{relative_url}?page=#{prev_page}"
    else
      relative_url
    end
  end

  def next_page_path
    "#{relative_url}?page=#{next_page}"
  end

  def absolute_url
    "#{Discourse.base_url_no_prefix}#{relative_url}"
  end

  def relative_url
    "#{@topic.relative_url}#{@print ? '/print' : ''}"
  end

  def page_title
    title = @topic.title
    if @post_number > 1
      title += " - "
      post = @topic.posts.find_by(post_number: @post_number)
      author = post&.user
      if author && @guardian.can_see_post?(post)
        title += I18n.t(
          "inline_oneboxer.topic_page_title_post_number_by_user",
          post_number: @post_number,
          username: author.username
        )
      else
        title += I18n.t(
          "inline_oneboxer.topic_page_title_post_number",
          post_number: @post_number
        )
      end
    end
    if SiteSetting.topic_page_title_includes_category
      if @topic.category_id != SiteSetting.uncategorized_category_id && @topic.category_id && @topic.category
        title += " - #{@topic.category.name}"
      elsif SiteSetting.tagging_enabled && @topic.tags.exists?
        title += " - #{@topic.tags.order('tags.topic_count DESC').first.name}"
      end
    end
    title
  end

  def title
    @topic.title
  end

  def desired_post
    return @desired_post if @desired_post.present?
    return nil if posts.blank?

    @desired_post = posts.detect { |p| p.post_number == @post_number }
    @desired_post ||= posts.first
    @desired_post
  end

  def summary(opts = {})
    return nil if desired_post.blank?
    # TODO, this is actually quite slow, should be cached in the post table
    excerpt = desired_post.excerpt(500, opts.merge(strip_links: true, text_entities: true))
    (excerpt || "").gsub(/\n/, ' ').strip
  end

  def read_time
    return nil if @post_number > 1 # only show for topic URLs

    if @topic.word_count && SiteSetting.read_time_word_count > 0
      [
        @topic.word_count / SiteSetting.read_time_word_count,
        @topic.posts_count * MIN_POST_READ_TIME / 60
      ].max.ceil
    end
  end

  def like_count
    return nil if @post_number > 1 # only show for topic URLs
    @topic.like_count
  end

  def published_time
    return nil if desired_post.blank?
    if desired_post.wiki && desired_post.post_number == 1 && desired_post.revisions.size > 0
      desired_post.revisions.last.updated_at.strftime('%FT%T%:z')
    else
      desired_post.created_at.strftime('%FT%T%:z')
    end
  end

  def image_url
    url = desired_post&.image_url if @post_number > 1
    url || @topic.image_url
  end

  def filter_posts(opts = {})
    if opts[:post_number].present?
      filter_posts_near(opts[:post_number].to_i)
    elsif opts[:post_ids].present?
      filter_posts_by_ids(opts[:post_ids])
    elsif opts[:filter_post_number].present?
      # Only used for megatopics where we do not load the entire post stream
      filter_posts_by_post_number(opts[:filter_post_number], opts[:asc])
    elsif opts[:best].present?
      # Only used for wordpress
      filter_best(opts[:best], opts)
    else
      filter_posts_paged(@page)
    end
  end

  def primary_group_names
    return @group_names if @group_names

    primary_group_ids = Set.new
    @posts.each do |p|
      primary_group_ids << p.user.primary_group_id if p.user.try(:primary_group_id)
    end

    result = {}
    unless primary_group_ids.empty?
      Group.where(id: primary_group_ids.to_a).pluck(:id, :name).each do |g|
        result[g[0]] = g[1]
      end
    end

    @group_names = result
  end

  # Filter to all posts near a particular post number
  def filter_posts_near(post_number)
    posts_before = (@limit.to_f / 4).floor
    posts_before = 1 if posts_before.zero?
    sort_order = get_sort_order(post_number)

    before_post_ids = @filtered_posts.reverse_order
      .where("posts.sort_order < ?", sort_order)
      .limit(posts_before)
      .pluck(:id)

    post_ids = before_post_ids + @filtered_posts
      .where("posts.sort_order >= ?", sort_order)
      .limit(@limit - before_post_ids.length)
      .pluck(:id)

    if post_ids.length < @limit
      post_ids = post_ids + @filtered_posts.reverse_order
        .where("posts.sort_order < ?", sort_order)
        .offset(before_post_ids.length)
        .limit(@limit - post_ids.length)
        .pluck(:id)
    end

    filter_posts_by_ids(post_ids)
  end

  def filter_posts_paged(page)
    page = [page, 1].max
    min = @limit * (page - 1)

    # Sometimes we don't care about the OP, for example when embedding comments
    min = 1 if min == 0 && @exclude_first

    filter_posts_by_ids(
      @filtered_posts
        .offset(min)
        .limit(@limit)
        .pluck(:id)
    )
  end

  def filter_best(max, opts = {})
    filter = FilterBestPosts.new(@topic, @filtered_posts, max, opts)
    @posts = filter.posts
    @filtered_posts = filter.filtered_posts
  end

  def read?(post_number)
    return true unless @user
    read_posts_set.include?(post_number)
  end

  def has_deleted?
    @predelete_filtered_posts.with_deleted
      .where("posts.deleted_at IS NOT NULL")
      .where("posts.post_number > 1")
      .exists?
  end

  def topic_user
    @topic_user ||= begin
      return nil if @user.blank?
      @topic.topic_users.find_by(user_id: @user.id)
    end
  end

  def has_bookmarks?
    return false if @user.blank?
    return false if @topic.trashed?
    bookmarks.any?
  end

  def bookmarks
    if SiteSetting.use_polymorphic_bookmarks
      @bookmarks ||= Bookmark.for_user_in_topic(@user, @topic.id).select(
        :id, :bookmarkable_id, :bookmarkable_type, :reminder_at, :name, :auto_delete_preference
      )
    else
      @bookmarks ||= @topic.bookmarks.where(user: @user).joins(:topic).select(
        :id, :post_id, "topics.id AS topic_id", :for_topic, :reminder_at, :name, :auto_delete_preference
      )
    end
  end

  MAX_PARTICIPANTS = 24

  def post_counts_by_user
    @post_counts_by_user ||= begin
      if is_mega_topic?
        {}
      else
        sql = <<~SQL
            SELECT user_id, count(*) AS count_all
              FROM posts
             WHERE topic_id = :topic_id
               AND post_type IN (:post_types)
               AND user_id IS NOT NULL
               AND posts.deleted_at IS NULL
               AND action_code IS NULL
          GROUP BY user_id
          ORDER BY count_all DESC
             LIMIT #{MAX_PARTICIPANTS}
        SQL

        Hash[*DB.query_single(sql, topic_id: @topic.id, post_types: Topic.visible_post_types(@guardian&.user))]
      end
    end
  end

  # if a topic has more that N posts no longer attempt to
  # get accurate participant count, instead grab cached count
  # from topic
  MAX_POSTS_COUNT_PARTICIPANTS = 500

  def participant_count
    @participant_count ||=
      begin
        if participants.size == MAX_PARTICIPANTS
          if @topic.posts_count > MAX_POSTS_COUNT_PARTICIPANTS
            @topic.participant_count
          else
            sql = <<~SQL
              SELECT COUNT(DISTINCT user_id)
              FROM posts
              WHERE id IN (:post_ids)
              AND user_id IS NOT NULL
            SQL
            DB.query_single(sql, post_ids: unfiltered_post_ids).first.to_i
          end
        else
          participants.size
        end
      end
  end

  def participants
    @participants ||= begin
      participants = {}
      User.where(id: post_counts_by_user.keys).includes(:primary_group).each { |u| participants[u.id] = u }
      participants
    end
  end

  def topic_allowed_group_ids
    @topic_allowed_group_ids ||= begin
      @topic.allowed_groups.map(&:id)
    end
  end

  def group_allowed_user_ids
    return @group_allowed_user_ids unless @group_allowed_user_ids.nil?

    @group_allowed_user_ids = GroupUser
      .where(group_id: topic_allowed_group_ids)
      .pluck('distinct user_id')
  end

  def category_group_moderator_user_ids
    @category_group_moderator_user_ids ||= begin
      if SiteSetting.enable_category_group_moderation? && @topic.category&.reviewable_by_group.present?
        posts_user_ids = Set.new(@posts.map(&:user_id))
        Set.new(
          @topic.category.reviewable_by_group.group_users.where(user_id: posts_user_ids).pluck('distinct user_id')
        )
      else
        Set.new
      end
    end
  end

  def all_post_actions
    @all_post_actions ||= PostAction.counts_for(@posts, @user)
  end

  def links
    @links ||= TopicLink.topic_map(@guardian, @topic.id)
  end

  def reviewable_counts
    @reviewable_counts ||= begin
      sql = <<~SQL
        SELECT
          target_id,
          MAX(r.id) reviewable_id,
          COUNT(*) total,
          SUM(CASE WHEN s.status = :pending THEN 1 ELSE 0 END) pending
        FROM
          reviewables r
        JOIN
          reviewable_scores s ON reviewable_id = r.id
        WHERE
          r.target_id IN (:post_ids) AND
          r.target_type = 'Post' AND
          COALESCE(s.reason, '') != 'category'
        GROUP BY
          target_id
      SQL

      counts = {}

      DB.query(
        sql,
        pending: ReviewableScore.statuses[:pending],
        post_ids: @posts.map(&:id)
      ).each do |row|
        counts[row.target_id] = {
          total: row.total,
          pending: row.pending,
          reviewable_id: row.reviewable_id
        }
      end

      counts
    end
  end

  def pending_posts
    @pending_posts ||= ReviewableQueuedPost.pending.where(created_by: @user, topic: @topic).order(:created_at)
  end

  def actions_summary
    return @actions_summary unless @actions_summary.nil?

    @actions_summary = []
    return @actions_summary unless post = posts&.first
    PostActionType.topic_flag_types.each do |sym, id|
      @actions_summary << {
        id: id,
        count: 0,
        hidden: false,
        can_act: @guardian.post_can_act?(post, sym)
      }
    end

    @actions_summary
  end

  def link_counts
    @link_counts ||= TopicLink.counts_for(@guardian, @topic, posts)
  end

  def pm_params
    @pm_params ||= TopicQuery.new(@user).get_pm_params(topic)
  end

  def suggested_topics
    if @include_suggested
      @suggested_topics ||= TopicQuery.new(@user).list_suggested_for(topic, pm_params: pm_params)
    else
      nil
    end
  end

  def related_messages
    if @include_related
      @related_messages ||= TopicQuery.new(@user).list_related_for(topic, pm_params: pm_params)
    else
      nil
    end
  end

  # This is pending a larger refactor, that allows custom orders
  # for now we need to look for the highest_post_number in the stream
  # the cache on topics is not correct if there are deleted posts at
  # the end of the stream (for mods), nor is it correct for filtered
  # streams
  def highest_post_number
    @highest_post_number ||= @filtered_posts.maximum(:post_number)
  end

  def recent_posts
    @filtered_posts.unscope(:order).by_newest.with_user.first(25)
  end

  # Returns an array of [id, days_ago] tuples.
  # `days_ago` is there for the timeline calculations.
  def filtered_post_stream
    @filtered_post_stream ||= begin
      posts = @filtered_posts
      columns = [:id]

      if !is_mega_topic?
        columns << '(EXTRACT(EPOCH FROM CURRENT_TIMESTAMP - posts.created_at) / 86400)::INT AS days_ago'
      end

      posts.pluck(*columns)
    end
  end

  def filtered_post_ids
    @filtered_post_ids ||= filtered_post_stream.map do |tuple|
      if is_mega_topic?
        tuple
      else
        tuple[0]
      end
    end
  end

  def unfiltered_post_ids
    @unfiltered_post_ids ||=
      begin
        if @contains_gaps
          unfiltered_posts.pluck(:id)
        else
          filtered_post_ids
        end
      end
  end

  def filtered_post_id(post_number)
    @filtered_posts.where(post_number: post_number).pluck_first(:id)
  end

  def is_mega_topic?
    @is_mega_topic ||= (@topic.posts_count >= MEGA_TOPIC_POSTS_COUNT)
  end

  def last_post_id
    @filtered_posts.reverse_order.pluck_first(:id)
  end

  def current_post_number
    if highest_post_number.present?
      post_number > highest_post_number ? highest_post_number : post_number
    end
  end

  def queued_posts_count
    ReviewableQueuedPost.viewable_by(@user).where(topic_id: @topic.id).pending.count
  end

  def published_page
    @topic.published_page
  end

  protected

  def read_posts_set
    @read_posts_set ||= begin
      result = Set.new
      return result unless @user.present?
      return result unless topic_user.present?

      post_numbers = PostTiming
        .where(topic_id: @topic.id, user_id: @user.id)
        .where(post_number: @posts.pluck(:post_number))
        .pluck(:post_number)

      post_numbers.each { |pn| result << pn }
      result
    end
  end

  private

  def calculate_page
    posts_count = is_mega_topic? ? @post_number : unfiltered_posts.where("post_number <= ?", @post_number).count
    ((posts_count - 1) / @limit) + 1
  end

  def get_sort_order(post_number)
    sql = <<~SQL
      SELECT posts.sort_order
      FROM posts
      WHERE posts.post_number = #{post_number.to_i}
      AND posts.topic_id = #{@topic.id.to_i}
      LIMIT 1
    SQL

    sort_order = DB.query_single(sql).first

    if !sort_order
      sql = <<~SQL
        SELECT posts.sort_order
        FROM posts
        WHERE posts.topic_id = #{@topic.id.to_i}
        ORDER BY @(post_number - #{post_number.to_i})
        LIMIT 1
      SQL

      sort_order = DB.query_single(sql).first
    end

    sort_order
  end

  def filter_post_types(posts)
    return posts.where(post_type: Post.types[:regular]) if @only_regular

    visible_types = Topic.visible_post_types(@user)

    if @user.present?
      posts.where("posts.user_id = ? OR post_type IN (?)", @user.id, visible_types)
    else
      posts.where(post_type: visible_types)
    end
  end

  def filter_posts_by_post_number(post_number, asc)
    sort_order = get_sort_order(post_number)

    posts =
      if asc
        @filtered_posts.where("sort_order > ?", sort_order)
      else
        @filtered_posts.reverse_order.where("sort_order < ?", sort_order)
      end

    posts = posts.limit(@limit) if !@skip_limit
    filter_posts_by_ids(posts.pluck(:id))

    @posts = @posts.reverse_order if !asc
  end

  def filter_posts_by_ids(post_ids)
    @posts = Post.where(id: post_ids, topic_id: @topic.id)
      .includes(
        { user: :primary_group },
        :reply_to_user,
        :deleted_by,
        :incoming_email,
        :topic,
        :image_upload
      )

    @posts = apply_default_scope(@posts)
    @posts = filter_post_types(@posts)
    @posts = @posts.with_deleted if @guardian.can_see_deleted_posts?(@topic.category)
    @posts
  end

  def find_topic(topic_or_topic_id)
    if topic_or_topic_id.is_a?(Topic)
      topic_or_topic_id
    else
      # with_deleted covered in #check_and_raise_exceptions
      finder = Topic.with_deleted.where(id: topic_or_topic_id).includes(:category)
      finder.first
    end
  end

  def unfiltered_posts
    result = filter_post_types(@topic.posts)
    result = result.with_deleted if @guardian.can_see_deleted_posts?(@topic.category)
    result = result.where("user_id IS NOT NULL") if @exclude_deleted_users
    result = result.where(hidden: false) if @exclude_hidden
    result
  end

  def apply_default_scope(scope)
    scope = scope.order(sort_order: :asc)

    self.class.custom_default_scopes.each do |block|
      scope = block.call(scope, self)
    end

    scope
  end

  def setup_filtered_posts
    # Certain filters might leave gaps between posts. If that's true, we can return a gap structure
    @contains_gaps = false
    @filtered_posts = unfiltered_posts

    if @user
      sql = <<~SQL
        SELECT ignored_user_id
        FROM ignored_users as ig
        INNER JOIN users as u ON u.id = ig.ignored_user_id
        WHERE ig.user_id = :current_user_id
          AND ig.ignored_user_id <> :current_user_id
          AND NOT u.admin
          AND NOT u.moderator
      SQL

      ignored_user_ids = DB.query_single(sql, current_user_id: @user.id)

      if ignored_user_ids.present?
        @filtered_posts = @filtered_posts.where.not("user_id IN (?) AND posts.post_number != 1", ignored_user_ids)
        @contains_gaps = true
      end
    end

    # Filters
    if @filter == 'summary'
      @filtered_posts = @filtered_posts.summary(@topic.id)
      @contains_gaps = true
    end

    if @filter.present? && @filter.to_s != 'summary' && TopicView.custom_filters[@filter].present?
      @filtered_posts = TopicView.custom_filters[@filter].call(@filtered_posts, self)
    end

    if @best.present?
      @filtered_posts = @filtered_posts.where('posts.post_type = ?', Post.types[:regular])
      @contains_gaps = true
    end

    # Username filters
    if @username_filters.present?
      usernames = @username_filters.map { |u| u.downcase }

      @filtered_posts = @filtered_posts.where('
        posts.post_number = 1
        OR posts.user_id IN (SELECT u.id FROM users u WHERE u.username_lower IN (?))
      ', usernames)

      @contains_gaps = true
    end

    # Filter replies
    if @replies_to_post_number.present?
      post_id = filtered_post_id(@replies_to_post_number.to_i)
      @filtered_posts = @filtered_posts.where('
        posts.post_number = 1
        OR posts.post_number = :post_number
        OR posts.reply_to_post_number = :post_number
        OR posts.id IN (SELECT pr.reply_post_id FROM post_replies pr WHERE pr.post_id = :post_id)', { post_number: @replies_to_post_number.to_i, post_id: post_id })

      @contains_gaps = true
    end

    # Show Only Top Level Replies
    if @filter_top_level_replies.present?
      @filtered_posts = @filtered_posts.where('
        posts.post_number > 1
        AND posts.reply_to_post_number IS NULL
      ')
    end

    # Filtering upwards
    if @filter_upwards_post_id.present?
      post = Post.find(@filter_upwards_post_id)
      post_ids = DB.query_single(<<~SQL, post_id: post.id, topic_id: post.topic_id)
      WITH RECURSIVE breadcrumb(id, reply_to_post_number) AS (
            SELECT p.id, p.reply_to_post_number FROM posts AS p
              WHERE p.id = :post_id
            UNION
              SELECT p.id, p.reply_to_post_number FROM posts AS p, breadcrumb
                WHERE breadcrumb.reply_to_post_number = p.post_number
                  AND p.topic_id = :topic_id
          )
      SELECT id from breadcrumb
      WHERE id <> :post_id
      ORDER by id
      SQL

      post_ids = (post_ids[(0 - SiteSetting.max_reply_history)..-1] || post_ids)
      post_ids.push(post.id)

      @filtered_posts = @filtered_posts.where('
        posts.post_number = 1
        OR posts.id IN (:post_ids)
        OR posts.id > :max_post_id', { post_ids: post_ids, max_post_id: post_ids.max })

      @contains_gaps = true
    end

    # Deleted
    # This should be last - don't want to tell the admin about deleted posts that clicking the button won't show
    # copy the filter for has_deleted? method
    @predelete_filtered_posts = @filtered_posts.spawn

    if @guardian.can_see_deleted_posts?(@topic.category) && !@show_deleted && has_deleted?
      @filtered_posts = @filtered_posts.where(
        "posts.deleted_at IS NULL OR posts.post_number = 1"
      )

      @contains_gaps = true
    end
  end

  def check_and_raise_exceptions(skip_staff_action)
    raise Discourse::NotFound if @topic.blank?
    # Special case: If the topic is private and the user isn't logged in, ask them
    # to log in!
    if @topic.present? && @topic.private_message? && @user.blank?
      raise Discourse::NotLoggedIn.new
    end
    # can user see this topic?
    raise Discourse::InvalidAccess.new("can't see #{@topic}", @topic) unless @guardian.can_see?(@topic)
    # log personal message views
    if SiteSetting.log_personal_messages_views && !skip_staff_action && @topic.present? && @topic.private_message? && @topic.all_allowed_users.where(id: @user.id).blank?
      unless UserHistory.where(acting_user_id: @user.id, action: UserHistory.actions[:check_personal_message], topic_id: @topic.id).where("created_at > ?", 1.hour.ago).exists?
        StaffActionLogger.new(@user).log_check_personal_message(@topic)
      end
    end
  end
end