My ruby prototype entity system

athena.rb

module Athena
  class Entity
    attr_reader :components

    def initialize
      @components = Hash.new
    end

    def add component
      @components[component.class] = component
      self
    end

    def remove component_class
      @components.delete(component_class)
      self
    end
  end


  class Component
  end


  class System
    attr_reader :nodes

    def initialize
      @nodes = Hash.new
    end

    def node klass
      @nodes[klass] = Array.new
    end

    def entity_added entity
      entity.components.each do |k,v|
        if @nodes.key?(k)
          @nodes[k] << v
        end
      end
    end

    def entity_removed entity
      entity.components.each do |k,v|
        if @nodes.key?(k)
          @nodes[k].delete(v)
        end
      end
    end

    def update delta
      true
    end
  end


  class Engine
    attr_reader :entities, :systems

    def initialize
      @entities = Array.new
      @systems = Hash.new
    end

    def add_entity entity
      @systems.each do |k,v|
        v.entity_added(entity)
      end
      @entities << entity
      self
    end

    def remove_entity entity
      @systems.each do |k,v|
        v.entity_removed(entity)
      end
      @entities.delete(entity)
      self
    end

    def add_system system
      @systems[system.class] = system
      self
    end

    def remove_system system_class
      @systems.delete(system_class)
      self
    end
  end
end

game.rb

require 'athena'

module Game
  module Components
    class Position < Athena::Component
      attr_accessor :x, :y

      def initialize x, y
        @x = x
        @y = y
      end
    end

    class Motion < Athena::Component
      attr_accessor :velocity, :direction

      def initialize velocity, direction
        @velocity = velocity
        @direction = direction
      end
    end
  end

  module Systems
    class Collision < Athena::System
      def initialize
        super

        node Game::Components::Position
        node Game::Components::Motion
      end
    end

    class Movement < Athena::System
      def initialize
        super

        node Game::Components::Position
        node Game::Components::Motion
      end
    end
  end

  def self.build_player
    entity = Athena::Entity.new
    entity.add(Game::Components::Position.new(0,0))
    entity.add(Game::Components::Motion.new(10,0))
    entity
  end

end

main.rb

require 'game'

engine = Athena::Engine.new
engine.add_system(Game::Systems::Collision.new)
engine.add_system(Game::Systems::Movement.new)

entity = Game.build_player

engine.add_entity(entity)

puts "Done"