class ECS
  class Entity
    attr_accessor :id

    def initialize(signature = 0)
      @id = ECS::Entity.generate_new_id
      self.class.all.push self
      self.class.signatures.push signature
      ECS::Components.entity_created(@id)
    end

    class <<self
      # All entities that exist
      def all
        @all ||= []
      end

      def id_queue
        @id_queue ||= []
      end

      def generate_new_id
        if id_queue.empty?
          all.size
        else
          id_queue.shift
        end
      end

      # What components a given entity uses
      def signatures
        @signatures ||= []
      end

      def destroy_entity(entity_id)
        if all[entity_id].nil?
          puts 'Entity can not be destroyed, id out of bounds'
        elsif entity_id < all.size - 1
          ECS::Components.constants.each do |constant|
            unless (signatures[entity_id] & ECS::Components::const_get(constant).id).zero?
              ECS::Components::const_get(constant).delete(entity_id)
            end
          end
          all[entity_id] = nil
          signatures[entity_id] = nil
          id_queue.push entity_id
        elsif entity_id == all.size - 1
          ECS::Components.constants.each do |constant|
            unless (signatures[entity_id] & ECS::Components::const_get(constant).id).zero?
              ECS::Components::const_get(constant).delete(entity_id)
            end
          end
          all.pop
          signatures.pop
        else
          puts 'Unknown error with destroy_entity, entity not destroyed'
        end
      end
    end
  end
end