module ActionDispatch::Http::Cache::Response

def etag
  @etag
end

def etag=(etag)
  key = ActiveSupport::Cache.expand_cache_key(etag)
  @etag = self["ETag"] = %("#{Digest::MD5.hexdigest(key)}")
end

def etag?
  @etag
end

def handle_conditional_get!
  if etag? || last_modified? || !@cache_control.empty?
    set_conditional_cache_control!
  elsif nonempty_ok_response?
    self.etag = body
    if request && request.etag_matches?(etag)
      self.status = 304
      self.body = []
    end
    set_conditional_cache_control!
  else
    headers["Cache-Control"] = "no-cache"
  end
end

def initialize(*)
  status, header, body = super
  @cache_control = {}
  @etag = self["ETag"]
  if cache_control = self["Cache-Control"]
    cache_control.split(/,\s*/).each do |segment|
      first, last = segment.split("=")
      last ||= true
      @cache_control[first.to_sym] = last
    end
  end
end

def last_modified
  if last = headers['Last-Modified']
    Time.httpdate(last)
  end
end

def last_modified=(utc_time)
  headers['Last-Modified'] = utc_time.httpdate
end

def last_modified?
  headers.include?('Last-Modified')
end

def nonempty_ok_response?
  @status == 200 && string_body?
end

def set_conditional_cache_control!
  return if self["Cache-Control"].present?
  control = @cache_control
  if control.empty?
    headers["Cache-Control"] = DEFAULT_CACHE_CONTROL
  elsif @cache_control[:no_cache]
    headers["Cache-Control"] = "no-cache"
  else
    extras  = control[:extras]
    max_age = control[:max_age]
    options = []
    options << "max-age=#{max_age.to_i}" if max_age
    options << (control[:public] ? "public" : "private")
    options << "must-revalidate" if control[:must_revalidate]
    options.concat(extras) if extras
    headers["Cache-Control"] = options.join(", ")
  end
end

def string_body?
  !@blank && @body.respond_to?(:all?) && @body.all? { |part| part.is_a?(String) }
end