Clean up method_missing and friends

In particular, filter_attr_accessor was kind of getting out of hand.

I don't like how the setup helpers all take almost the same arguments.

lib/active_interaction/base.rb

@@ -106,57 +106,61 @@ def self.run!(options = {})
     end
 
     # @private
-    def self.method_missing(filter_type, *args, &block)
-      klass = Filter.factory(filter_type)
+    def self.method_missing(type, *args, &block)
+      filter = Filter.factory(type)
       options = args.last.is_a?(Hash) ? args.pop : {}
       args.each do |attribute|
-        filter_attr_accessor(klass, attribute, options, &block)
-
-        filter_validator(attribute, filter_type, klass, options, &block)
+        set_up_reader(attribute, filter, options, &block)
+        set_up_writer(attribute, filter, options, &block)
+        set_up_validator(attribute, type, filter, options, &block)
       end
     end
     private_class_method :method_missing
 
     # @private
-    def self.filter_attr_accessor(filter, attribute, options, &block)
-      filter_attr_writer = "_filter__#{attribute}="
-      define_method(filter_attr_writer) do |value|
-        filtered_value =
-          begin
-            filter.prepare(attribute, value, options, &block)
-          rescue InvalidValue, MissingValue
-            value
-          end
-
-        instance_variable_set("@#{attribute}", filtered_value)
-      end
-      private filter_attr_writer
-
-      attr_writer attribute
-
-      default_value = nil
+    def self.set_up_reader(attribute, filter, options, &block)
+      default = nil
       if options.has_key?(:default)
         begin
-          default_value = filter.prepare(
-            attribute, options.delete(:default), options, &block)
+          default = filter.
+            prepare(attribute, options.delete(:default), options, &block)
         rescue InvalidValue
           raise InvalidDefaultValue
         end
       end
 
       define_method(attribute) do
-        instance_variable_name = "@#{attribute}"
-        if instance_variable_defined?(instance_variable_name)
-          instance_variable_get(instance_variable_name)
+        symbol = "@#{attribute}"
+        if instance_variable_defined?(symbol)
+          instance_variable_get(symbol)
         else
-          default_value
+          default
         end
       end
     end
-    private_class_method :filter_attr_accessor
+    private_class_method :set_up_reader
+
+    # @private
+    def self.set_up_writer(attribute, filter, options, &block)
+      attr_writer attribute
+
+      writer = "_filter__#{attribute}="
+
+      define_method(writer) do |value|
+        value =
+          begin
+            filter.prepare(attribute, value, options, &block)
+          rescue InvalidValue, MissingValue
+            value
+          end
+        instance_variable_set("@#{attribute}", value)
+      end
+      private writer
+    end
+    private_class_method :set_up_writer
 
     # @private
-    def self.filter_validator(attribute, type, filter, options, &block)
+    def self.set_up_validator(attribute, type, filter, options, &block)
       validator = "_validate__#{attribute}__#{type}"
 
       validate validator
@@ -173,6 +177,6 @@ def self.filter_validator(attribute, type, filter, options, &block)
       end
       private validator
     end
-    private_class_method :filter_validator
+    private_class_method :set_up_validator
   end
 end