ecs_game_simple_system.rb

module GameEcs
  class EcsSystem
    def self.system_for_query(query, &block)
      new(query, &block)
    end
    
    def initialize(query=Query.none, &block)
      @query = query
      @system_block = block
    end

    def update(entity_store, *args)
      before_update(entity_store, *args)
      entity_store.query.each do |ent|
        each(ent, *args)
      end
      after_update(entity_store, *args)
    end

    def before_update(entity_store, *args)
    end
    def after_update(entity_store, *args)
    end
    def update_each(entity_store, ent, *args)
      # handle a single update of an ent
      @system_block.call(entity_store, ent, *args)
    end
  end

end
include GameEcs
MovementSystem = EcsSystem.system_for_query( Q.musts(Position, Velocity) ) do |store, ent, dt, input|
  pos,vel = ent.components
  pos.x += vel.x * dt
  pos.y += vel.y * dt
end

# long hand via subclassing
class MovementSystem < EcsSystem
  def after_update(store, *args)
    # whatever
  end
  def update_each(store, ent, dt, input)
    Q.each_entity(Position, Velocity) do
      pos,vel = ent.components
      pos.x += vel.x * dt
      pos.y += vel.y * dt
    end
  end
end