class Sprockets::Helpers::RailsHelper::AssetPaths

def asset_for(source, ext)
  source = source.to_s
  return nil if is_uri?(source)
  source = rewrite_extension(source, nil, ext)
  asset_environment[source]
rescue Sprockets::FileOutsidePaths
  nil
end

def digest_for(logical_path)
  if digest_assets && asset_digests && (digest = asset_digests[logical_path])
    return digest
  end
  if compile_assets
    if digest_assets && asset = asset_environment[logical_path]
      return asset.digest_path
    end
    return logical_path
  else
    raise AssetNotPrecompiledError.new("#{logical_path} isn't precompiled")
  end
end

def rewrite_asset_path(source, dir, options = {})
  if source[0] == ?/
    source
  else
    source = digest_for(source) unless options[:digest] == false
    source = File.join(dir, source)
    source = "/#{source}" unless source =~ /^\//
    source
  end
end

def rewrite_extension(source, dir, ext)
  source_ext = File.extname(source)
  if ext && source_ext != ".#{ext}"
    if !source_ext.empty? && asset_environment[source]
      source
    else
      "#{source}.#{ext}"
    end
  else
    source
  end
end