Abstract the Tempfile generation into a factory

lib/paperclip.rb

@@ -34,6 +34,7 @@ require 'paperclip/processor'
 require 'paperclip/tempfile'
 require 'paperclip/thumbnail'
 require 'paperclip/interpolations'
+require 'paperclip/tempfile_factory'
 require 'paperclip/style'
 require 'paperclip/attachment'
 require 'paperclip/attachment_options'

lib/paperclip/io_adapters/abstract_adapter.rb

 module Paperclip
   class AbstractAdapter
-    ILLEGAL_FILENAME_CHARACTERS = /^~/
-
     private
 
     def destination
-      if @destination.nil?
-        extension = File.extname(original_filename)
-        basename = File.basename(original_filename, extension)
-        basename = basename.gsub(ILLEGAL_FILENAME_CHARACTERS, '_')
-        dest = Tempfile.new([basename, extension])
-        dest.binmode
-        @destination = dest
-      end
-      @destination
+      @destination ||= TempfileFactory.new.generate(original_filename)
     end
 
     def copy_to_tempfile(src)

lib/paperclip/tempfile_factory.rb

+module Paperclip
+  class TempfileFactory
+
+    ILLEGAL_FILENAME_CHARACTERS = /^~/
+
+    def generate(name)
+      @name = name
+      file = Tempfile.new([basename, extension])
+      file.binmode
+      file
+    end
+
+    def extension
+      File.extname(@name)
+    end
+
+    def basename
+      File.basename(@name, extension).gsub(ILLEGAL_FILENAME_CHARACTERS, '_')
+    end
+  end
+end

test/tempfile_factory_test.rb

+require './test/helper'
+
+class Paperclip::TempfileFactoryTest < Test::Unit::TestCase
+  should "be able to generate a tempfile with the right name" do
+    file = subject.generate("omg.png")
+  end
+  should "be able to generate a tempfile with the right name with a tilde at the beginning" do
+    file = subject.generate("~omg.png")
+  end
+  should "be able to generate a tempfile with the right name with a tilde at the end" do
+    file = subject.generate("omg.png~")
+  end
+end