require 'digest/md5'
require 'base64'

class Oplop
  attr_reader :master, :label, :length

  LEGACY_LENGTH = 8
  DEFAULT_LENGTH = 16

  def self.password(args={})
    self.new(args).password
  end

  def initialize(args={})
    @master = args[:master]
    @label = args[:label]
    @length = args[:length] || DEFAULT_LENGTH

    if @label =~ /^([0-9]*)?\*/
      (@length, @label) = @label.split('*')
      @length = length.to_i
      @length = LEGACY_LENGTH if length <= 0
    end
  end

  def master_label
    @master_label ||= '%s%s' % [ master, label ]
  end

  def password
    password = Base64.urlsafe_encode64(Digest::MD5.digest(master_label))

    if password.respond_to?(:encode)
      password = password.encode('UTF-8')
    end

    if m = password.match(/\d+/)
      password = '%s%s' % [ m[0], password ] if (m.begin(0) >= length)
    else
      password = '1%s' % password
    end

    password[0,length]
  end
end