class Net::HTTPHeader::DigestAuthenticator

def a1
  a1_user_realm_pwd =  [@username, @response['realm'], @password].join(':')
  if use_md5_sess?
    [ md5(a1_user_realm_pwd), @response['nonce'], @cnonce ].join(':')
  else
    a1_user_realm_pwd
  end
end

def a2
  [@method, @path].join(':')
end

def algorithm_present?
  @response.key?('algorithm') && !@response['algorithm'].empty?
end

def authorization_header
  @cnonce = md5(random)
  header = [
    %(Digest username="#{@username}"),
    %(realm="#{@response['realm']}"),
    %(nonce="#{@response['nonce']}"),
    %(uri="#{@path}"),
    %(response="#{request_digest}")
  ]
  header << %(algorithm="#{@response['algorithm']}") if algorithm_present?
  if qop_present?
    header << %(cnonce="#{@cnonce}")
    header << %(qop="#{@response['qop']}")
    header << 'nc=00000001'
  end
  header << %(opaque="#{@response['opaque']}") if opaque_present?
  header
end

def cookie_header
  @cookies
end

def initialize(username, password, method, path, response_header)
  @username = username
  @password = password
  @method   = method
  @path     = path
  @response = parse(response_header)
  @cookies  = parse_cookies(response_header)
end

def md5(str)
  Digest::MD5.hexdigest(str)
end

def opaque_present?
  @response.key?('opaque') && !@response['opaque'].empty?
end

def parse(response_header)
  header = response_header['www-authenticate']
  header = header.gsub(/qop=(auth(?:-int)?)/, 'qop="\\1"')
  header =~ /Digest (.*)/
  params = {}
  if $1
    non_quoted = $1.gsub(/(\w+)="(.*?)"/) { params[$1] = $2 }
    non_quoted.gsub(/(\w+)=([^,]*)/) { params[$1] = $2 }
  end
  params
end

def parse_cookies(response_header)
  return [] unless response_header['Set-Cookie']
  cookies = response_header['Set-Cookie'].split('; ')
  cookies.reduce([]) do |ret, cookie|
    ret << cookie
    ret
  end
  cookies
end

def qop_present?
  @response.key?('qop') && !@response['qop'].empty?
end

def random
  format '%x', (Time.now.to_i + rand(65535))
end

def request_digest
  a = [md5(a1), @response['nonce'], md5(a2)]
  a.insert(2, '00000001', @cnonce, @response['qop']) if qop_present?
  md5(a.join(':'))
end

def use_md5_sess?
  algorithm_present? && @response['algorithm'] == 'MD5-sess'
end