module RSpec
  module Core
    # Shared example groups let you define common context and/or common
    # examples that you wish to use in multiple example groups.
    #
    # When defined, the shared group block is stored for later evaluation.
    # It can later be included in an example group either explicitly
    # (using `include_examples`, `include_context` or `it_behaves_like`)
    # or implicitly (via matching metadata).
    #
    # Named shared example groups are scoped based on where they are
    # defined. Shared groups defined in an example group are available
    # for inclusion in that example group or any child example groups,
    # but not in any parent or sibling example groups. Shared example
    # groups defined at the top level can be included from any example group.
    module SharedExampleGroup
      # @overload shared_examples(name, &block)
      #   @param name [String, Symbol, Module] identifer to use when looking up this shared group
      #   @param block The block to be eval'd
      # @overload shared_examples(name, metadata, &block)
      #   @param name [String, Symbol, Module] identifer to use when looking up this shared group
      #   @param metadata [Array<Symbol>, Hash] metadata to attach to this group; any example group
      #     with matching metadata will automatically include this shared example group.
      #   @param block The block to be eval'd
      # @overload shared_examples(metadata, &block)
      #   @param metadata [Array<Symbol>, Hash] metadata to attach to this group; any example group
      #     with matching metadata will automatically include this shared example group.
      #   @param block The block to be eval'd
      #
      # Stores the block for later use. The block will be evaluated
      # in the context of an example group via `include_examples`,
      # `include_context`, or `it_behaves_like`.
      #
      # @example
      #   shared_examples "auditable" do
      #     it "stores an audit record on save!" do
      #       expect { auditable.save! }.to change(Audit, :count).by(1)
      #     end
      #   end
      #
      #   describe Account do
      #     it_behaves_like "auditable" do
      #       let(:auditable) { Account.new }
      #     end
      #   end
      #
      # @see ExampleGroup.it_behaves_like
      # @see ExampleGroup.include_examples
      # @see ExampleGroup.include_context
      def shared_examples(name, *args, &block)
        top_level = self == ExampleGroup
        if top_level && RSpec.thread_local_metadata[:in_example_group]
          raise "Creating isolated shared examples from within a context is " +
                "not allowed. Remove `RSpec.` prefix or move this to a " +
                "top-level scope."
        end

        RSpec.world.shared_example_group_registry.add(self, name, *args, &block)
      end
      alias shared_context      shared_examples
      alias shared_examples_for shared_examples

      # @api private
      #
      # Shared examples top level DSL
      module TopLevelDSL
        # @private
        def self.definitions
          proc do
            def shared_examples(name, *args, &block)
              RSpec.world.shared_example_group_registry.add(:main, name, *args, &block)
            end
            alias shared_context      shared_examples
            alias shared_examples_for shared_examples
          end
        end

        # @private
        def self.exposed_globally?
          @exposed_globally ||= false
        end

        # @api private
        #
        # Adds the top level DSL methods to Module and the top level binding
        def self.expose_globally!
          return if exposed_globally?
          Core::DSL.change_global_dsl(&definitions)
          @exposed_globally = true
        end

        # @api private
        #
        # Removes the top level DSL methods to Module and the top level binding
        def self.remove_globally!
          return unless exposed_globally?

          Core::DSL.change_global_dsl do
            undef shared_examples
            undef shared_context
            undef shared_examples_for
          end

          @exposed_globally = false
        end

      end

      # @private
      class Registry
        def add(context, name, *metadata_args, &block)
          ensure_block_has_source_location(block) { CallerFilter.first_non_rspec_line }

          if valid_name?(name)
            warn_if_key_taken context, name, block
            shared_example_groups[context][name] = block
          else
            metadata_args.unshift name
          end

          unless metadata_args.empty?
            mod = Module.new
            (class << mod; self; end).__send__(:define_method, :included) do |host|
              host.class_exec(&block)
            end
            RSpec.configuration.include mod, *metadata_args
          end
        end

        def find(lookup_contexts, name)
          lookup_contexts.each do |context|
            found = shared_example_groups[context][name]
            return found if found
          end

          shared_example_groups[:main][name]
        end

      private

        def shared_example_groups
          @shared_example_groups ||= Hash.new { |hash, context| hash[context] = {} }
        end

        def valid_name?(candidate)
          case candidate
            when String, Symbol, Module then true
            else false
          end
        end

        def warn_if_key_taken(context, key, new_block)
          return unless existing_block = shared_example_groups[context][key]

          RSpec.warn_with <<-WARNING.gsub(/^ +\|/, ''), :call_site => nil
            |WARNING: Shared example group '#{key}' has been previously defined at:
            |  #{formatted_location existing_block}
            |...and you are now defining it at:
            |  #{formatted_location new_block}
            |The new definition will overwrite the original one.
          WARNING
        end

        def formatted_location(block)
          block.source_location.join ":"
        end

        if Proc.method_defined?(:source_location)
          def ensure_block_has_source_location(block); end
        else # for 1.8.7
          def ensure_block_has_source_location(block)
            source_location = yield.split(':')
            block.extend Module.new { define_method(:source_location) { source_location } }
          end
        end
      end
    end
  end

  instance_exec(&Core::SharedExampleGroup::TopLevelDSL.definitions)
end