class RSpec::Mocks::InstanceMethodStasher

def handle_restoration_failures
  yield
rescue TypeError
  RSpec.warn_with(
    "RSpec failed to properly restore a partial double (#{@object.inspect}) " \
    "to its original state due to a known bug in MRI 2.0.0-p195 & p247 " \
    "(https://bugs.ruby-lang.org/issues/8686). This object may remain " \
    "screwed up for the rest of this process. Please upgrade to 2.0.0-p353 or above.",
    :call_site => nil, :use_spec_location_as_call_site => true
  )
end

def handle_restoration_failures
  # No known reasons for restoration to fail on other rubies.
  yield
end

def initialize(object, method)
  @object = object
  @method = method
  @klass = (class << object; self; end)
  @original_method = nil
  @method_is_stashed = false
end

def method_defined_directly_on_klass?
  method_defined_on_klass? && method_owned_by_klass?
end

def method_defined_on_klass?(klass=@klass)
  MethodReference.method_defined_at_any_visibility?(klass, @method)
end

def method_is_stashed?
  @method_is_stashed
end

def method_is_stashed?
  !!@original_method
end

def method_owned_by_klass?
  owner = @klass.instance_method(@method).owner
  # On Ruby 2.0.0+ the owner of a method on a class which has been
  # `prepend`ed may actually be an instance, e.g.
  # `#<MyClass:0x007fbb94e3cd10>`, rather than the expected `MyClass`.
  owner = owner.class unless Module === owner
  # On some 1.9s (e.g. rubinius) aliased methods
  # can report the wrong owner. Example:
  # class MyClass
  #   class << self
  #     alias alternate_new new
  #   end
  # end
  #
  # MyClass.owner(:alternate_new) returns `Class` when incorrect,
  # but we need to consider the owner to be `MyClass` because
  # it is not actually available on `Class` but is on `MyClass`.
  # Hence, we verify that the owner actually has the method defined.
  # If the given owner does not have the method defined, we assume
  # that the method is actually owned by @klass.
  #
  # On 1.8, aliased methods can also report the wrong owner. Example:
  # module M
  #   def a; end
  #   module_function :a
  #   alias b a
  #   module_function :b
  # end
  # The owner of M.b is the raw Module object, instead of the expected
  # singleton class of the module
  return true if RUBY_VERSION < '1.9' && owner == @object
  owner == @klass || !(method_defined_on_klass?(owner))
end

def restore
  return unless @method_is_stashed
  if @klass.__send__(:method_defined?, @method)
    @klass.__send__(:undef_method, @method)
  end
  @klass.__send__(:alias_method, @method, stashed_method_name)
  @klass.__send__(:remove_method, stashed_method_name)
  @method_is_stashed = false
end

def restore
  return unless @original_method
  if @klass.__send__(:method_defined?, @method)
    @klass.__send__(:undef_method, @method)
  end
  handle_restoration_failures do
    @klass.__send__(:define_method, @method, @original_method)
  end
  @original_method = nil
end

def stash
  return if !method_defined_directly_on_klass? || @method_is_stashed
  @klass.__send__(:alias_method, stashed_method_name, @method)
  @method_is_stashed = true
end

def stash
  return unless method_defined_directly_on_klass?
  @original_method ||= ::RSpec::Support.method_handle_for(@object, @method)
  @klass.__send__(:undef_method, @method)
end

def stashed_method_name
  "obfuscated_by_rspec_mocks__#{@method}"
end