module ActionDispatch::Http::Cache::Response

def cache_control_headers
  cache_control = {}
  cache_control_segments.each do |segment|
    directive, argument = segment.split('=', 2)
    if SPECIAL_KEYS.include? directive
      key = directive.tr('-', '_')
      cache_control[key.to_sym] = argument || true
    else
      cache_control[:extras] ||= []
      cache_control[:extras] << segment
    end
  end
  cache_control
end

def cache_control_segments
  if cache_control = self[CACHE_CONTROL]
    cache_control.delete(' ').split(',')
  else
    []
  end
end

def date
  if date_header = headers[DATE]
    Time.httpdate(date_header)
  end
end

def date=(utc_time)
  headers[DATE] = utc_time.httpdate
end

def date?
  headers.include?(DATE)
end

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

def handle_conditional_get!
  if etag? || last_modified? || !@cache_control.empty?
    set_conditional_cache_control!
  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 prepare_cache_control!
  @cache_control = cache_control_headers
  @etag = self[ETAG]
end

def set_conditional_cache_control!
  control = {}
  cc_headers = cache_control_headers
  if extras = cc_headers.delete(:extras)
    @cache_control[:extras] ||= []
    @cache_control[:extras] += extras
    @cache_control[:extras].uniq!
  end
  control.merge! cc_headers
  control.merge! @cache_control
  if control.empty?
    headers[CACHE_CONTROL] = DEFAULT_CACHE_CONTROL
  elsif control[:no_cache]
    headers[CACHE_CONTROL] = NO_CACHE
    if control[:extras]
      headers[CACHE_CONTROL] += ", #{control[:extras].join(', ')}"
    end
  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