module Sprockets::ProcessorUtils

def call_processor(processor, input)

Returns a Hash with :data and other processor metadata key/values.

input - Hash of input data to pass to processor
processor - Processor callables

Public: Invoke processor. 
def call_processor(processor, input)
  metadata = (input[:metadata] || {}).dup
  metadata[:data] = input[:data]
  case result = processor.call({data: "", metadata: {}}.merge(input))
  when NilClass
    metadata
  when Hash
    metadata.merge(result)
  when String
    metadata.merge(data: result)
  else
    raise TypeError, "invalid processor return type: #{result.class}"
  end
end

def call_processors(processors, input)

Returns a Hash with :data and other processor metadata key/values.

input - Hash of input data to pass to each processor
processors - Array of processor callables

bundle.call(uglify.call(coffee.call(input)))

Think about:
The right to left order processing mirrors standard function composition.

Public: Invoke list of processors in right to left order. 
def call_processors(processors, input)
  data = input[:data] || ""
  metadata = (input[:metadata] || {}).dup
  processors.reverse_each do |processor|
    result = call_processor(processor, input.merge(data: data, metadata: metadata))
    data = result.delete(:data)
    metadata.merge!(result)
  end
  metadata.merge(data: data)
end

def compose_processors(*processors)

Returns a composed Proc.

processors - Array of processors callables

Public: Compose processors in right to left order. 
def compose_processors(*processors)
  context = self
  if processors.length == 1
    obj = method(:call_processor).to_proc.curry[processors.first]
  else
    obj = method(:call_processors).to_proc.curry[processors]
  end
  metaclass = (class << obj; self; end)
  metaclass.send(:define_method, :cache_key) do
    context.processors_cache_keys(processors)
  end
  obj
end

def processor_cache_key(processor)

Returns JSON serializable key or nil.

processor - Processor function

Internal: Get processor defined cached key. 
def processor_cache_key(processor)
  processor.cache_key if processor.respond_to?(:cache_key)
end

def processors_cache_keys(processors)

Returns Array of JSON serializable keys.

processors - Array of processor functions

Internal: Get combined cache keys for set of processors. 
def processors_cache_keys(processors)
  processors.map { |processor| processor_cache_key(processor) }
end