module Polyamorous::JoinDependencyExtensions

def build(associations, base_klass)
  associations.map do |name, right|
    if name.is_a? Join
      reflection = find_reflection base_klass, name.name
      reflection.check_validity!
      reflection.check_eager_loadable!
      klass = if reflection.polymorphic?
        name.klass || base_klass
      else
        reflection.klass
      end
      JoinAssociation.new(reflection, build(right, klass), name.klass, name.type)
    else
      reflection = find_reflection base_klass, name
      reflection.check_validity!
      reflection.check_eager_loadable!
      if reflection.polymorphic?
        raise ActiveRecord::EagerLoadPolymorphicError.new(reflection)
      end
      JoinAssociation.new(reflection, build(right, reflection.klass))
    end
  end
end