diff --git a/judge/scripts/lib/engine.rb b/judge/scripts/lib/engine.rb
new file mode 100644
--- /dev/null
+++ b/judge/scripts/lib/engine.rb
@@ -0,0 +1,138 @@
+require 'fileutils'
+
+module Grader
+
+  #
+  # A grader engine grades a submission, against anything: a test
+  # data, or a user submitted test data.  It uses two helpers objects:
+  # room_maker and reporter.
+  #
+  class Engine
+    
+    attr_writer :room_maker
+    attr_writer :reporter
+
+    def initialize(room_maker=nil, reporter=nil)
+      @config = Grader::Configuration.get_instance
+
+      @room_maker = room_maker || Grader::SubmissionRoomMaker.new 
+      @reporter = reporter || Grader::SubmissionReporter.new
+    end
+    
+    # takes a submission, asks room_maker to produce grading directories,
+    # calls grader scripts, and asks reporter to save the result
+    def grade(submission)
+      current_dir = `pwd`.chomp
+
+      user = submission.user
+      problem = submission.problem
+
+      # TODO: will have to create real exception for this
+      if user==nil or problem == nil
+        @reporter.report_error(submission,"Grading error: problem with submission")
+        #raise "engine: user or problem is nil"
+      end
+
+      # TODO: this is another hack so that output only task can be judged
+      if submission.language!=nil
+        language = submission.language.name
+        lang_ext = submission.language.ext
+      else
+        language = 'c'
+        lang_ext = 'c'
+      end
+
+      # FIX THIS
+      talk 'some hack on language'
+      if language == 'cpp'
+        language = 'c++'
+      end
+
+      # COMMENT: should it be only source.ext?
+      if problem!=nil
+        source_name = "#{problem.name}.#{lang_ext}"
+      else
+        source_name = "source.#{lang_ext}"
+      end
+
+      begin
+        grading_dir = @room_maker.produce_grading_room(submission)
+        @room_maker.save_source(submission,source_name)
+        problem_home = @room_maker.find_problem_home(submission)
+
+        # puts "GRADING DIR: #{grading_dir}"
+        # puts "PROBLEM DIR: #{problem_home}"
+
+        copy_log = copy_script(problem_home)
+      
+        call_judge(problem_home,language,grading_dir,source_name)
+
+        @reporter.report(submission,"#{grading_dir}/test-result")
+
+        clear_script(copy_log,problem_home)
+
+      rescue RuntimeError => msg
+        @reporter.report_error(submission,"Grading error: #{msg}")
+
+      ensure
+        @room_maker.clean_up(submission)
+        Dir.chdir(current_dir)   # this is really important
+      end
+    end
+    
+    protected
+    
+    def talk(str)
+      if @config.talkative
+        puts str
+      end
+    end
+
+    def call_judge(problem_home,language,grading_dir,fname)
+      ENV['PROBLEM_HOME'] = problem_home
+      
+      talk grading_dir
+      Dir.chdir grading_dir
+      cmd = "#{problem_home}/script/judge #{language} #{fname}"
+      talk "CMD: #{cmd}"
+      system(cmd)
+    end
+
+    def get_std_script_dir
+      GRADER_ROOT + '/std-script'
+    end
+
+    def copy_script(problem_home)
+      script_dir = "#{problem_home}/script"
+      std_script_dir = get_std_script_dir
+
+      raise "std-script directory not found" if !FileTest.exist?(std_script_dir)
+
+      scripts = Dir[std_script_dir + '/*']
+      
+      copied = []
+
+      scripts.each do |s|
+        fname = File.basename(s)
+        if !FileTest.exist?("#{script_dir}/#{fname}")
+          copied << fname
+          system("cp #{s} #{script_dir}")
+        end
+      end
+      
+      return copied
+    end
+    
+    def clear_script(log,problem_home)
+      log.each do |s|
+        system("rm #{problem_home}/script/#{s}")
+      end
+    end
+
+    def mkdir_if_does_not_exist(dirname)
+      Dir.mkdir(dirname) if !FileTest.exist?(dirname)
+    end
+    
+  end
+  
+end