module Rack::Utils

def select_best_encoding(available_encodings, accept_encoding)
  # http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
  expanded_accept_encoding = []
  accept_encoding.each do |m, q|
    preference = available_encodings.index(m) || available_encodings.size
    if m == "*"
      (available_encodings - accept_encoding.map(&:first)).each do |m2|
        expanded_accept_encoding << [m2, q, preference]
      end
    else
      expanded_accept_encoding << [m, q, preference]
    end
  end
  encoding_candidates = expanded_accept_encoding
    .sort_by { |_, q, p| [-q, p] }
    .map!(&:first)
  unless encoding_candidates.include?("identity")
    encoding_candidates.push("identity")
  end
  expanded_accept_encoding.each do |m, q|
    encoding_candidates.delete(m) if q == 0.0
  end
  (encoding_candidates & available_encodings)[0]
end