module RSpec
  module Support
    # Provides recursive constant lookup methods useful for
    # constant stubbing.
    module RecursiveConstMethods
      # We only want to consider constants that are defined directly on a
      # particular module, and not include top-level/inherited constants.
      # Unfortunately, the constant API changed between 1.8 and 1.9, so
      # we need to conditionally define methods to ignore the top-level/inherited
      # constants.
      #
      # Given:
      #   class A; B = 1; end
      #   class C < A; end
      #
      # On 1.8:
      #   - C.const_get("Hash") # => ::Hash
      #   - C.const_defined?("Hash") # => false
      #   - C.constants # => ["B"]
      #   - None of these methods accept the extra `inherit` argument
      # On 1.9:
      #   - C.const_get("Hash") # => ::Hash
      #   - C.const_defined?("Hash") # => true
      #   - C.const_get("Hash", false) # => raises NameError
      #   - C.const_defined?("Hash", false) # => false
      #   - C.constants # => [:B]
      #   - C.constants(false) #=> []
      if Module.method(:const_defined?).arity == 1
        def const_defined_on?(mod, const_name)
          mod.const_defined?(const_name)
        end

        def get_const_defined_on(mod, const_name)
          return mod.const_get(const_name) if const_defined_on?(mod, const_name)

          raise NameError, "uninitialized constant #{mod.name}::#{const_name}"
        end

        def constants_defined_on(mod)
          mod.constants.select { |c| const_defined_on?(mod, c) }
        end
      else
        def const_defined_on?(mod, const_name)
          mod.const_defined?(const_name, false)
        end

        def get_const_defined_on(mod, const_name)
          mod.const_get(const_name, false)
        end

        def constants_defined_on(mod)
          mod.constants(false)
        end
      end

      def recursive_const_get(const_name)
        normalize_const_name(const_name).split('::').inject(Object) do |mod, name|
          get_const_defined_on(mod, name)
        end
      end

      def recursive_const_defined?(const_name)
        parts = normalize_const_name(const_name).split('::')
        parts.inject([Object, '']) do |(mod, full_name), name|
          yield(full_name, name) if block_given? && !(Module === mod)
          return false unless const_defined_on?(mod, name)
          [get_const_defined_on(mod, name), [mod.name, name].join('::')]
        end
      end

      def normalize_const_name(const_name)
        const_name.sub(/\A::/, '')
      end
    end
  end
end