module RSpec
  module Mocks
    # @private
    class InstanceMethodStasher
      def initialize(klass, method)
        @klass = klass
        @method = method

        @method_is_stashed = false
      end

      # @private
      def method_is_stashed?
        @method_is_stashed
      end

      # @private
      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

      private

      # @private
      def method_defined_directly_on_klass?
        method_defined_on_klass? && method_owned_by_klass?
      end

      # @private
      def method_defined_on_klass?(klass = @klass)
        klass.method_defined?(@method) || klass.private_method_defined?(@method)
      end

      if ::UnboundMethod.method_defined?(:owner)
        # @private
        def method_owned_by_klass?
          owner = @klass.instance_method(@method).owner
          # On 1.8 (and 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` on 1.8,
          # 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.
          owner == @klass || !(method_defined_on_klass?(owner))
        end
      else
        # @private
        def method_owned_by_klass?
          # On 1.8.6, which does not support Method#owner, we have no choice but
          # to assume it's defined on the klass even if it may be defined on
          # a superclass.
          true
        end
      end

      public

      # @private
      def stashed_method_name
        "obfuscated_by_rspec_mocks__#{@method}"
      end

      # @private
      def restore
        return unless @method_is_stashed

        @klass.__send__(:alias_method, @method, stashed_method_name)
        @klass.__send__(:remove_method, stashed_method_name)
        @method_is_stashed = false
      end
    end
  end
end