danbooru/app/models/favorite_group.rb

class FavoriteGroup < ApplicationRecord
  validates_uniqueness_of :name, :case_sensitive => false, :scope => :creator_id
  validates_format_of :name, :with => /\A[^,]+\Z/, :message => "cannot have commas"
  belongs_to :creator, class_name: "User"
  before_validation :normalize_name
  before_validation :strip_name
  validate :creator_can_create_favorite_groups, :on => :create
  validate :validate_number_of_posts
  validate :validate_posts

  array_attribute :post_ids, parse: /\d+/, cast: :to_i

  module SearchMethods
    def for_post(post_id)
      where_array_includes_any(:post_ids, [post_id])
    end

    def name_matches(name)
      name = normalize_name(name)
      name = "*#{name}*" unless name =~ /\*/
      where_ilike(:name, name)
    end

    def visible(user)
      where(is_public: true).or(where(creator_id: user.id))
    end

    def default_order
      order(name: :asc)
    end

    def search(params)
      q = super
      q = q.visible(CurrentUser.user)
      q = q.search_attributes(params, :name, :is_public, :post_ids, :creator)

      if params[:name_matches].present?
        q = q.name_matches(params[:name_matches])
      end

      q.apply_default_order(params)
    end
  end

  extend SearchMethods

  def creator_can_create_favorite_groups
    if creator.favorite_groups.count >= creator.favorite_group_limit
      error = "You can only keep up to #{creator.favorite_group_limit} favorite groups."
      if !creator.is_platinum?
        error += " Upgrade your account to create more."
      end
      self.errors.add(:base, error)
    end
  end

  def validate_number_of_posts
    if post_count > 10_000
      errors[:base] << "Favorite groups can have up to 10,000 posts each"
    end
  end

  def validate_posts
    added_post_ids = post_ids - post_ids_was
    existing_post_ids = Post.where(id: added_post_ids).pluck(:id)
    nonexisting_post_ids = added_post_ids - existing_post_ids

    if nonexisting_post_ids.present?
      errors[:base] << "Cannot add invalid post(s) to favgroup: #{nonexisting_post_ids.to_sentence}"
    end

    duplicate_post_ids = post_ids.group_by(&:itself).transform_values(&:size).select { |id, count| count > 1 }.keys
    if duplicate_post_ids.present?
      errors[:base] << "Favgroup already contains post #{duplicate_post_ids.to_sentence}"
    end
  end

  def self.normalize_name(name)
    name.gsub(/[[:space:]]+/, "_")
  end

  def normalize_name
    self.name = FavoriteGroup.normalize_name(name)
  end

  def self.find_by_name_or_id(name, user)
    if name =~ /\A\d+\z/
      find_by(id: name)
    else
      user.favorite_groups.where_iequals(:name, normalize_name(name)).first
    end
  end

  def self.find_by_name_or_id!(name, user)
    find_by_name_or_id(name, user) or raise ActiveRecord::RecordNotFound
  end

  def strip_name
    self.name = name.to_s.strip
  end

  def pretty_name
    name.tr("_", " ")
  end

  def posts
    favgroup_posts = FavoriteGroup.where(id: id).joins("CROSS JOIN unnest(favorite_groups.post_ids) WITH ORDINALITY AS row(post_id, favgroup_index)").select(:post_id, :favgroup_index)
    posts = Post.joins("JOIN (#{favgroup_posts.to_sql}) favgroup_posts ON favgroup_posts.post_id = posts.id").order("favgroup_posts.favgroup_index ASC")
  end

  def add!(post)
    with_lock do
      update!(post_ids: post_ids + [post.id])
    end
  end

  def remove!(post)
    with_lock do
      update!(post_ids: post_ids - [post.id])
    end
  end

  def post_count
    post_ids.size
  end

  def first_post?(post_id)
    post_id == post_ids.first
  end

  def last_post?(post_id)
    post_id == post_ids.last
  end

  def previous_post_id(post_id)
    return nil if first_post?(post_id) || !contains?(post_id)

    n = post_ids.index(post_id) - 1
    post_ids[n]
  end

  def next_post_id(post_id)
    return nil if last_post?(post_id) || !contains?(post_id)

    n = post_ids.index(post_id) + 1
    post_ids[n]
  end

  def last_page
    (post_count / CurrentUser.user.per_page.to_f).ceil
  end

  def contains?(post_id)
    post_ids.include?(post_id)
  end

  def editable_by?(user)
    creator_id == user.id
  end

  def viewable_by?(user)
    creator_id == user.id || is_public
  end
end