An attempt at creating an Entity-Component-System architecture, in Ruby

ruby-ecs.rb

require 'securerandom'

Entity = Struct.new(:uuid)

class Component
  attr_accessor :entity_uuid

  def initialize(entity_uuid)
    @entity_uuid = entity_uuid
    ComponentsStore.register_component(self)
  end
end

class System
  class << self
    def update(payload = nil)
      SystemsStore.all.each do |systems|
        systems.each do |sistem|
          sistem.update(payload)
        end
      end
    end
  end

  def initialize(*component_types)
    @component_types = component_types
    SystemsStore.register_system(self, @component_types)
  end

  def update(payload = nil)
    raise 'You must implement this method!'
  end
end

class SystemsStore
  class << self
    def all
      instance.systems.values
    end

    def register_system(sistem, component_types)
      instance.systems[component_types] ||= []
      instance.systems[component_types] << sistem
      self
    end

    private

    def instance
      @instance ||= new
    end
  end

  attr_reader :systems

  private

  def initialize
    @systems = {}
  end
end

class ComponentsStore
  class << self
    def fetch_by_types(types)
      Array(types).map do |type|
        instance.components[type]
      end.flatten
    end

    def register_component(component)
      instance.components[component.class] ||= []
      instance.components[component.class] << component
      self
    end

    private

    def instance
      @instance ||= new
    end
  end

  attr_reader :components

  private

  def initialize
    @components = {}
  end
end

RSpec.describe 'Ruby Entity-Component-System architecture' do
  class YoloComponent < Component
  end

  class YoloSystem < System
    def initialize
      super(YoloComponent)
    end

    def update(payload = nil)
      ComponentsStore.fetch_by_types(*@component_types).each do |component|
        puts "#{component.class} says: Yolo!"
      end
    end
  end

  before do
    @yolo_entity = Entity.new(SecureRandom.uuid)
    @yolo_component = YoloComponent.new(@yolo_entity.uuid)
    @yolo_system = YoloSystem.new
  end

  describe System do
    it "doesn't crash" do
      expect { described_class.update }.not_to raise_error
    end

    it 'sends updates to all systems' do
      allow(@yolo_system).to receive(:update)
      described_class.update
      expect(@yolo_system).to have_received(:update).exactly(1).times
    end
  end
end