turbovault-app/app/models/collection.rb

class Collection < ApplicationRecord
  # Associations
  belongs_to :user
  belongs_to :parent_collection, class_name: "Collection", optional: true
  has_many :subcollections, class_name: "Collection", foreign_key: "parent_collection_id", dependent: :destroy
  has_many :collection_games, dependent: :destroy
  has_many :games, through: :collection_games

  # Validations
  validates :name, presence: true
  validate :cannot_be_own_parent
  validate :subcollection_depth_limit

  # Scopes
  scope :root_collections, -> { where(parent_collection_id: nil) }

  # Instance methods
  def game_count
    games.count
  end

  def total_game_count
    game_count + subcollections.sum(&:total_game_count)
  end

  def root?
    parent_collection_id.nil?
  end

  def subcollection?
    parent_collection_id.present?
  end

  private

  def cannot_be_own_parent
    if parent_collection_id.present? && parent_collection_id == id
      errors.add(:parent_collection_id, "cannot be itself")
    end
  end

  def subcollection_depth_limit
    if parent_collection.present? && parent_collection.parent_collection.present?
      errors.add(:parent_collection_id, "cannot nest more than one level deep")
    end
  end
end