Allow converting a configuration object back to a Hash

While this is somewhat complicated code, I am sure it'll come in handy -
not just for testing the `config.yml` file.

lib/alchemy/configuration.rb

@@ -49,8 +49,33 @@ def set_from_yaml(file)
       )
     end
 
+    def to_h
+      self.class.defined_options.map do |option|
+        [option, send(option)]
+      end.concat(
+        self.class.defined_configurations.map do |configuration|
+          [configuration, send(configuration).to_h]
+        end
+      ).to_h
+    end
+
     class << self
+      def defined_configurations = []
+
+      def defined_options = []
+
       def configuration(name, configuration_class)
+        # The defined preferences on a class are all those defined directly on
+        # that class as well as those defined on ancestors.
+        # We store these as a class instance variable on each class which has a
+        # preference. super() collects preferences defined on ancestors.
+        singleton_configurations = (@defined_singleton_configurations ||= [])
+        singleton_configurations << name.to_sym
+
+        define_singleton_method :defined_configurations do
+          super() + singleton_configurations
+        end
+
         define_method(name) do
           unless instance_variable_get(:"@#{name}")
             send(:"#{name}=", configuration_class.new)
@@ -68,6 +93,17 @@ def configuration(name, configuration_class)
       end
 
       def option(name, type, default: nil)
+        # The defined preferences on a class are all those defined directly on
+        # that class as well as those defined on ancestors.
+        # We store these as a class instance variable on each class which has a
+        # preference. super() collects preferences defined on ancestors.
+        singleton_options = (@defined_singleton_options ||= [])
+        singleton_options << name.to_sym
+
+        define_singleton_method :defined_options do
+          super() + singleton_options
+        end
+
         define_method(name) do
           unless instance_variable_defined?(:"@#{name}")
             send(:"#{name}=", default)

spec/libraries/alchemy/configuration_spec.rb

@@ -228,6 +228,13 @@
     subject { configuration.get(:mail_success_page) }
 
     it { is_expected.to eq("thanks") }
+
+    it "can be converted to a Hash" do
+      expect(configuration.to_h).to eq(
+        mail_success_page: "thanks",
+        link_target_options: ["blank"]
+      )
+    end
   end
 
   describe "nested configurations" do
@@ -256,5 +263,11 @@
       expect(configuration.uploader.upload_limit).to eq(30)
       expect(configuration.uploader.file_size_limit).to eq(80)
     end
+
+    it "can be converted to a Hash" do
+      expect(configuration.to_h).to eq(
+        uploader: {file_size_limit: 100, upload_limit: 50}
+      )
+    end
   end
 end