Simple Haml content caching

cache.rb

# Amadeusz Juskowiak <amadeusz@amanointeractive.com> 2012 - MIT License

# 1. Put inside helpers do .. end
# 2. Set CACHE_DIR to somewhere writable and private (like CACHE_DIR=File.dirname(__FILE__) + '/tmp'
# 3. Use it! You can use fragment_expire to remove cache with given name.
#
# Example:
#   %h1 foo
#   = cache_fragment(:report, 300) do
#     - data = get_data_slowly
#     %h2 my super extensive table generation
# 
# In example above, block will be cached for 300 seconds.
# 
# Remember: 
#   Cache entries are identified only by their name - so no matter where you access your
#   :report it will be the same report! This means you have to be careful with sensible data.
#   If you want cache different data in same view use something like
#     "#{@user._id}/#{@basket._id}" as a key.
#
# Have fun!

def cache_fragment(name, expires, &haml)
  filename = CACHE_DIR + '/' + name.to_s + '.cache'
  
  now = Time.now
  result = 'Cache Error!'
  needs_caching = true
  
  if File.file? filename
    if (((now - File.mtime(filename)).to_i) >= expires)
      needs_caching = true
    else
      needs_caching = false
      result = File.read(filename)
    end
  end
  
  if needs_caching
    f = File.new(filename, 'w')
    f.write(result = capture_haml(&haml))
    f.close
  end
  
  result
end

def fragment_expire(name)
  filename = CACHE_DIR + '/' + name.to_s + '.cache'
  
  if File.file? filename
    File.unlink filename rescue (return false)
    
    return true
  end
  
  false
end