Refactor PropertyTranslation for readability

The original implementation of PropertyTranslation was heavily reliant
longer methods that added a lot of cognitive load for understanding what
should be happening at any given point. This refactor gives names for all
of the steps that happen at each step to make it easier to reason about
bugs and additions.

1 files changed, 48 insertions, 24 deletions

diff --git a/lib/hashie/extensions/dash/property_translation.rb b/lib/hashie/extensions/dash/property_translation.rb
index 2d28080..25b6499 100644
--- a/lib/hashie/extensions/dash/property_translation.rb
+++ b/lib/hashie/extensions/dash/property_translation.rb
@@ -40,7 +40,7 @@ module Hashie
       module PropertyTranslation
         def self.included(base)
           base.instance_variable_set(:@transforms, {})
-          base.instance_variable_set(:@translations_hash, {})
+          base.instance_variable_set(:@translations_hash, ::Hash.new { |hash, key| hash[key] = {} })
           base.extend(ClassMethods)
           base.send(:include, InstanceMethods)
         end
@@ -72,21 +72,16 @@ module Hashie
           def property(property_name, options = {})
             super
 
-            if options[:from]
-              if property_name == options[:from]
-                raise ArgumentError, "Property name (#{property_name}) and :from option must not be the same"
-              end
-
-              translations_hash[options[:from]] ||= {}
-              translations_hash[options[:from]][property_name] = options[:with] || options[:transform_with]
+            from = options[:from]
+            converter = options[:with]
+            transformer = options[:transform_with]
 
-              define_method "#{options[:from]}=" do |val|
-                self.class.translations_hash[options[:from]].each do |name, with|
-                  self[name] = with.respond_to?(:call) ? with.call(val) : val
-                end
-              end
-            elsif options[:transform_with].respond_to? :call
-              transforms[property_name] = options[:transform_with]
+            if from
+              fail_self_transformation_error!(property_name) if property_name == from
+              define_translation(from, property_name, converter || transformer)
+              define_writer_for_source_property(from)
+            elsif valid_transformer?(transformer)
+              transforms[property_name] = transformer
             end
           end
 
@@ -103,26 +98,49 @@ module Hashie
           end
 
           def translations
-            @translations ||= {}.tap do |h|
+            @translations ||= {}.tap do |translations|
               translations_hash.each do |(property_name, property_translations)|
-                h[property_name] = if property_translations.size > 1
-                                     property_translations.keys
-                                   else
-                                     property_translations.keys.first
-                                   end
+                translations[property_name] =
+                  if property_translations.size > 1
+                    property_translations.keys
+                  else
+                    property_translations.keys.first
+                  end
               end
             end
           end
 
           def inverse_translations
-            @inverse_translations ||= {}.tap do |h|
+            @inverse_translations ||= {}.tap do |translations|
               translations_hash.each do |(property_name, property_translations)|
-                property_translations.each_key do |k|
-                  h[k] = property_name
+                property_translations.each_key do |key|
+                  translations[key] = property_name
                 end
               end
             end
           end
+
+          private
+
+          def define_translation(from, property_name, translator)
+            translations_hash[from][property_name] = translator
+          end
+
+          def define_writer_for_source_property(property)
+            define_method "#{property}=" do |val|
+              __translations[property].each do |name, with|
+                self[name] = with.respond_to?(:call) ? with.call(val) : val
+              end
+            end
+          end
+
+          def fail_self_transformation_error!(property_name)
+            raise ArgumentError, "Property name (#{property_name}) and :from option must not be the same"
+          end
+
+          def valid_transformer?(transformer)
+            transformer.respond_to? :call
+          end
         end
 
         module InstanceMethods
@@ -156,6 +174,12 @@ module Hashie
             fail_no_property_error!(property) unless self.class.property?(property)
             true
           end
+
+          private
+
+          def __translations
+            self.class.translations_hash
+          end
         end
       end
     end