class Precacher

# File lib/precacher.rb, line 5
def self.file_cache(filename, &blk)
  # get hash of file if it does exist.
  hash_pre = Digest::MD5.file filename if File.exists?(filename)
  
  # run blk  # TODO pass in file stream type object???
  data = blk.call()

  # get hash of new data to compare
  hash_post = Digest::MD5.hexdigest data

  if hash_post.to_s != hash_pre.to_s
    File.open(filename, 'w') do |f|
      f << data
    end
    true
  else
    false
  end
end