module RSpec
  module Core
    module SharedExampleGroup

      # @overload shared_examples(name, &block)
      # @overload shared_examples(name, tags, &block)
      #
      # Creates and stores (but does not evaluate) the block.
      #
      # @see ExampleGroup.include_examples
      # @see ExampleGroup.include_context
      def shared_examples(*args, &block)
        if [String, Symbol, Module].any? {|cls| cls === args.first }
          object = args.shift
          ensure_shared_example_group_name_not_taken(object)
          RSpec.world.shared_example_groups[object] = block
        end

        unless args.empty?
          mod = Module.new
          (class << mod; self; end).send(:define_method, :extended) do |host|
            host.class_eval(&block)
          end
          RSpec.configuration.extend(mod, *args)
        end
      end

      alias_method :shared_context,      :shared_examples
      alias_method :share_examples_for,  :shared_examples
      alias_method :shared_examples_for, :shared_examples

      def share_as(name, &block)
        if Object.const_defined?(name)
          mod = Object.const_get(name)
          raise_name_error unless mod.created_from_caller(caller)
        end

        mod = Module.new do
          @shared_block = block
          @caller_line = caller.last

          def self.created_from_caller(other_caller)
            @caller_line == other_caller.last
          end

          def self.included(kls)
            kls.describe(&@shared_block)
            kls.children.first.metadata[:shared_group_name] = name
          end
        end

        shared_const = Object.const_set(name, mod)
        RSpec.world.shared_example_groups[shared_const] = block
      end

    private

      def raise_name_error
        raise NameError, "The first argument (#{name}) to share_as must be a legal name for a constant not already in use."
      end

      def ensure_shared_example_group_name_not_taken(name)
        if RSpec.world.shared_example_groups.has_key?(name)
          raise ArgumentError.new("Shared example group '#{name}' already exists")
        end
      end

    end
  end
end

include RSpec::Core::SharedExampleGroup