Deduplicate column argument parsing between extractors

.rubocop_todo.yml

@@ -124,11 +124,11 @@ Style/Documentation:
     - 'lib/comma/object.rb'
     - 'lib/comma/relation.rb'
 
-# Offense count: 3
+# Offense count: 2
 Style/MissingRespondToMissing:
   Exclude:
     - 'lib/comma/data_extractor.rb'
-    - 'lib/comma/header_extractor.rb'
+    - 'lib/comma/extractor.rb'
 
 # Offense count: 1
 # This cop supports safe autocorrection (--autocorrect).

lib/comma/data_extractor.rb

@@ -49,28 +49,24 @@ def method_missing(_symbol, *_args, &_block)
       end
     end
 
-    def method_missing(sym, *args, &block)
-      @results << ExtractValueFromInstance.new(@instance).extract(sym, &block) if
-        args.blank?
-
-      args.each do |arg|
-        case arg
-        when Hash
-          arg.each do |k, _v|
-            @results << ExtractValueFromAssociationOfInstance.new(@instance, sym).extract(k, &block)
-          end
-        when Symbol
-          @results << ExtractValueFromAssociationOfInstance.new(@instance, sym).extract(arg, &block)
-        when String
-          @results << ExtractValueFromInstance.new(@instance).extract(sym, &block)
-        else
-          raise "Unknown data symbol #{arg.inspect}"
-        end
-      end
-    end
-
     def __static_column__(_header = nil, &block)
       @results << (block ? yield(@instance) : nil)
     end
+
+    private
+
+    def extract_column(method, association: nil, **, &block)
+      value_extractor(association).extract(method, &block)
+    end
+
+    def value_extractor(association)
+      return ExtractValueFromInstance.new(@instance) unless association
+
+      ExtractValueFromAssociationOfInstance.new(@instance, association)
+    end
+
+    def column_kind
+      'data'
+    end
   end
 end

lib/comma/extractor.rb

@@ -37,6 +37,26 @@ def __use__(style)
       end
     end
 
+    def method_missing(sym, *args, &block)
+      if args.empty?
+        @results << extract_column(sym, &block)
+        return
+      end
+
+      args.each do |arg|
+        case arg
+        when Hash
+          arg.each { |k, v| @results << extract_column(k, association: sym, label: v, &block) }
+        when Symbol
+          @results << extract_column(arg, association: sym, label: arg, &block)
+        when String
+          @results << extract_column(sym, label: arg, &block)
+        else
+          raise "Unknown #{column_kind} symbol #{arg.inspect}"
+        end
+      end
+    end
+
     private
 
     def convert_to_data_value(result)

lib/comma/header_extractor.rb

@@ -16,31 +16,22 @@ class HeaderExtractor < Extractor
     end
     self.value_humanizer = DEFAULT_VALUE_HUMANIZER
 
-    def method_missing(sym, *args, &_block)
-      model_class = @instance.class
-      @results << value_humanizer.call(sym, model_class) if args.blank?
-      args.each do |arg|
-        case arg
-        when Hash
-          arg.each do |_k, v|
-            @results << value_humanizer.call(v, get_association_class(model_class, sym))
-          end
-        when Symbol
-          @results << value_humanizer.call(arg, get_association_class(model_class, sym))
-        when String
-          @results << value_humanizer.call(arg, model_class)
-        else
-          raise "Unknown header symbol #{arg.inspect}"
-        end
-      end
-    end
-
     def __static_column__(header = '', &_block)
       @results << header
     end
 
     private
 
+    def extract_column(method, association: nil, label: nil, **)
+      model_class = @instance.class
+      target_class = association ? get_association_class(model_class, association) : model_class
+      value_humanizer.call(label || method, target_class)
+    end
+
+    def column_kind
+      'header'
+    end
+
     def get_association_class(model_class, association)
       return unless model_class.respond_to?(:reflect_on_association)