discourse/app/models/category_list.rb

require_dependency 'pinned_check'

class CategoryList
  include ActiveModel::Serialization

  cattr_accessor :preloaded_topic_custom_fields
  self.preloaded_topic_custom_fields = Set.new

  attr_accessor :categories,
                :uncategorized,
                :draft,
                :draft_key,
                :draft_sequence

  def initialize(guardian = nil, options = {})
    @guardian = guardian || Guardian.new
    @options = options

    find_relevant_topics if options[:include_topics]
    find_categories

    prune_empty
    prune_muted
    find_user_data
    sort_unpinned
    trim_results

    if preloaded_topic_custom_fields.present?
      displayable_topics = @categories.map(&:displayable_topics)
      displayable_topics.flatten!
      displayable_topics.compact!

      if displayable_topics.present?
        Topic.preload_custom_fields(
          displayable_topics,
          preloaded_topic_custom_fields
        )
      end
    end
  end

  def preload_key
    "categories_list".freeze
  end

  def self.order_categories(categories)
    if SiteSetting.fixed_category_positions
      categories.order(:position, :id)
    else
      allowed_category_ids = categories.pluck(:id) << nil # `nil` is necessary to include categories without any associated topics
      categories.left_outer_joins(:featured_topics)
        .where(topics: { category_id: allowed_category_ids })
        .group('categories.id')
        .order("max(topics.bumped_at) DESC NULLS LAST")
        .order('categories.id ASC')
    end
  end

  private

  def find_relevant_topics
    @topics_by_id = {}
    @topics_by_category_id = {}

    category_featured_topics = CategoryFeaturedTopic.select([:category_id, :topic_id]).order(:rank)

    @all_topics = Topic.where(id: category_featured_topics.map(&:topic_id))
    @all_topics = @all_topics.includes(:last_poster) if @options[:include_topics]
    @all_topics.each do |t|
      # hint for the serializer
      t.include_last_poster = true if @options[:include_topics]
      @topics_by_id[t.id] = t
    end

    category_featured_topics.each do |cft|
      @topics_by_category_id[cft.category_id] ||= []
      @topics_by_category_id[cft.category_id] << cft.topic_id
    end
  end

  def find_categories
    @categories = Category.includes(
      :uploaded_background,
      :uploaded_logo,
      :topic_only_relative_url,
      subcategories: [:topic_only_relative_url]
    ).secured(@guardian)

    @categories = @categories.where("categories.parent_category_id = ?", @options[:parent_category_id].to_i) if @options[:parent_category_id].present?

    @categories = self.class.order_categories(@categories)

    @categories = @categories.to_a

    category_user = {}
    default_notification_level = nil
    unless @guardian.anonymous?
      category_user = Hash[*CategoryUser.where(user: @guardian.user).pluck(:category_id, :notification_level).flatten]
      default_notification_level = CategoryUser.notification_levels[:regular]
    end

    allowed_topic_create = Set.new(Category.topic_create_allowed(@guardian).pluck(:id))
    @categories.each do |category|
      category.notification_level = category_user[category.id] || default_notification_level
      category.permission = CategoryGroup.permission_types[:full] if allowed_topic_create.include?(category.id)
      category.has_children = category.subcategories.present?
    end

    if @options[:parent_category_id].blank?
      subcategories = {}
      to_delete = Set.new
      @categories.each do |c|
        if c.parent_category_id.present?
          subcategories[c.parent_category_id] ||= []
          subcategories[c.parent_category_id] << c.id
          to_delete << c
        end
      end
      @categories.each { |c| c.subcategory_ids = subcategories[c.id] }
      @categories.delete_if { |c| to_delete.include?(c) }
    end

    if @topics_by_category_id
      @categories.each do |c|
        topics_in_cat = @topics_by_category_id[c.id]
        if topics_in_cat.present?
          c.displayable_topics = []
          topics_in_cat.each do |topic_id|
            topic = @topics_by_id[topic_id]
            if topic.present? && @guardian.can_see?(topic)
              # topic.category is very slow under rails 4.2
              topic.association(:category).target = c
              c.displayable_topics << topic
            end
          end
        end
      end
    end
  end

  def prune_empty
    return if SiteSetting.allow_uncategorized_topics
    @categories.delete_if { |c| c.uncategorized? && c.displayable_topics.blank? }
  end

  def prune_muted
    @categories.delete_if { |c| c.notification_level == CategoryUser.notification_levels[:muted] }
  end

  # Attach some data for serialization to each topic
  def find_user_data
    if @guardian.current_user && @all_topics.present?
      topic_lookup = TopicUser.lookup_for(@guardian.current_user, @all_topics)
      @all_topics.each { |ft| ft.user_data = topic_lookup[ft.id] }
    end
  end

  # Put unpinned topics at the end of the list
  def sort_unpinned
    if @guardian.current_user && @all_topics.present?
      @categories.each do |c|
        next if c.displayable_topics.blank? || c.displayable_topics.size <= c.num_featured_topics
        unpinned = []
        c.displayable_topics.each do |t|
          unpinned << t if t.pinned_at && PinnedCheck.unpinned?(t, t.user_data)
        end
        unless unpinned.empty?
          c.displayable_topics = (c.displayable_topics - unpinned) + unpinned
        end
      end
    end
  end

  def trim_results
    @categories.each do |c|
      next if c.displayable_topics.blank?
      c.displayable_topics = c.displayable_topics[0, c.num_featured_topics]
    end
  end

end