feat: add Nack::Component and Nack::Middleware

lib/nack.rb

@@ -1,8 +1,10 @@
 # frozen_string_literal: true
 
 require_relative "nack/version"
+require_relative "nack/component"
 require_relative "nack/error"
 require_relative "nack/headers"
+require_relative "nack/middleware"
 require_relative "nack/mime"
 require_relative "nack/query_parser"
 require_relative "nack/request"

lib/nack/component.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module Nack
+  class Component
+    def to_app
+      prepare_app
+      self
+    end
+
+    private
+
+    def prepare_app
+    end
+  end
+end

lib/nack/middleware.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Nack
+  class Middleware < Component
+    def call(request)
+      @app.call(request)
+    end
+
+    def wrap(app)
+      middleware = clone(freeze: false)
+      middleware.app = app
+      middleware
+    end
+
+    protected
+
+    attr_writer :app
+  end
+end

test/spec_component.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+describe Nack::Component do
+  it "returns itself as the app" do
+    component = Nack::Component.new
+    component.to_app.must_be_same_as component
+  end
+
+  it "prepares itself as the app" do
+    component = Class.new(Nack::Component) do
+      attr_reader :prepared
+
+      def prepare_app
+        @prepared = true
+      end
+    end.new
+    component.to_app.prepared.must_equal true
+  end
+end

test/spec_middleware.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+describe Nack::Middleware do
+  it "wraps an app in a copy of a frozen instance" do
+    Nack::Middleware.new.freeze.wrap(->(request) { "#{request}b" }).call("a").must_equal "ab"
+  end
+
+  it "wraps an app in a copy keeping its singleton methods" do
+    middleware = Nack::Middleware.new
+    def middleware.call(request) = "#{super}c"
+    middleware.wrap(->(request) { "#{request}b" }).call("a").must_equal "abc"
+  end
+end