module Sprockets::Transformers

def compose_transformers(transformers, types)

Returns Processor.

types - Array of mime type steps
transformers - Two level Hash of a source mime type to a target mime type

function.
Internal: Compose multiple transformer steps into a single processor 
def compose_transformers(transformers, types)
  if types.length < 2
    raise ArgumentError, "too few transform types: #{types.inspect}"
  end
  i = 0
  processors = []
  loop do
    src = types[i]
    dst = types[i+1]
    break unless src && dst
    unless processor = transformers[src][dst]
      raise ArgumentError, "missing transformer for type: #{src} to #{dst}"
    end
    processors.concat config[:postprocessors][src]
    processors << processor
    processors.concat config[:preprocessors][dst]
    i += 1
  end
  if processors.size > 1
    compose_processors(*processors.reverse)
  elsif processors.size == 1
    processors.first
  end
end