class Erubis::Engine

def self.load_file(filename, properties={})

#
# or filname + 'cache' is used as default.
# cachefile name can be specified with properties[:cachename],
# this method create code cache file automatically.
# load file, write cache file, and return engine object.
# 
def self.load_file(filename, properties={})
  cachename = properties[:cachename] || (filename + '.cache')
  properties[:filename] = filename
  timestamp = File.mtime(filename)
  if test(?f, cachename) && timestamp == File.mtime(cachename)
    engine = self.new(nil, properties)
    engine.src = File.read(cachename)
  else
    input = File.open(filename, 'rb') {|f| f.read }
    engine = self.new(input, properties)
    tmpname = cachename + rand().to_s[1,8]
    File.open(tmpname, 'wb') {|f| f.write(engine.src) }
    File.rename(tmpname, cachename)
    File.utime(timestamp, timestamp, cachename)
  end
  engine.src.untaint   # ok?
  return engine
end