class ActiveRecord::Associations::Builder::CollectionAssociation

def self.define_callback(model, callback_name, name, options)
  full_callback_name = "#{callback_name}_for_#{name}"
  callback_values = Array(options[callback_name.to_sym])
  method_defined = model.respond_to?(full_callback_name)
  # If there are no callbacks, we must also check if a superclass had
  # previously defined this association
  return if callback_values.empty? && !method_defined
  unless method_defined
    model.class_attribute(full_callback_name, instance_accessor: false, instance_predicate: false)
  end
  callbacks = callback_values.map do |callback|
    case callback
    when Symbol
      ->(method, owner, record) { owner.send(callback, record) }
    when Proc
      ->(method, owner, record) { callback.call(owner, record) }
    else
      ->(method, owner, record) { callback.send(method, owner, record) }
    end
  end
  model.send "#{full_callback_name}=", callbacks
end

def self.define_callbacks(model, reflection)
  super
  name    = reflection.name
  options = reflection.options
  CALLBACKS.each { |callback_name|
    define_callback(model, callback_name, name, options)
  }
end

def self.define_extensions(model, name, &block)
  if block_given?
    extension_module_name = "#{name.to_s.camelize}AssociationExtension"
    extension = Module.new(&block)
    model.const_set(extension_module_name, extension)
  end
end

def self.define_readers(mixin, name)
  super
  mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
    def #{name.to_s.singularize}_ids
      association(:#{name}).ids_reader
    end
  CODE
end

def self.define_writers(mixin, name)
  super
  mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
    def #{name.to_s.singularize}_ids=(ids)
      association(:#{name}).ids_writer(ids)
    end
  CODE
end

def self.valid_options(options)
  super + [:before_add, :after_add, :before_remove, :after_remove, :extend]
end