class ActiveRecord::Associations::Builder::Association

def self.build(*args, &block)
  new(*args, &block).build
end

def build; end }

def build
  validate_options
  define_accessors
  configure_dependency if options[:dependent]
  @reflection = model.create_reflection(macro, name, scope, options, model)
  super # provides an extension point
  @reflection
end

def configure_dependency
  unless valid_dependent_options.include? options[:dependent]
    raise ArgumentError, "The :dependent option must be one of #{valid_dependent_options}, but is :#{options[:dependent]}"
  end
  if options[:dependent] == :restrict
    ActiveSupport::Deprecation.warn(
      "The :restrict option is deprecated. Please use :restrict_with_exception instead, which " \
      "provides the same functionality."
    )
  end
  mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
    def #{macro}_dependent_for_#{name}
      association(:#{name}).handle_dependency
    end
  CODE
  model.before_destroy "#{macro}_dependent_for_#{name}"
end

def define_accessors
  define_readers
  define_writers
end

def define_readers
  mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
    def #{name}(*args)
      association(:#{name}).reader(*args)
    end
  CODE
end

def define_writers
  mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
    def #{name}=(value)
      association(:#{name}).writer(value)
    end
  CODE
end

def initialize(model, name, scope, options)
  raise ArgumentError, "association names must be a Symbol" unless name.kind_of?(Symbol)
  @model   = model
  @name    = name
  if scope.is_a?(Hash)
    @scope   = nil
    @options = scope
  else
    @scope   = scope
    @options = options
  end
  if @scope && @scope.arity == 0
    prev_scope = @scope
    @scope = proc { instance_exec(&prev_scope) }
  end
end

def macro
  raise NotImplementedError
end

def mixin
  @model.generated_feature_methods
end

def valid_dependent_options
  raise NotImplementedError
end

def valid_options
  Association.valid_options
end

def validate_options
  options.assert_valid_keys(valid_options)
end