class Devise::TokenGenerator

def digest(klass, column, value)
  value.present? && OpenSSL::HMAC.hexdigest(@digest, key_for(column), value.to_s)
end

def generate(klass, column)
  key = key_for(column)
  loop do
    raw = Devise.friendly_token
    enc = OpenSSL::HMAC.hexdigest(@digest, key, raw)
    break [raw, enc] unless klass.to_adapter.find_first({ column => enc })
  end
end

def initialize(key_generator, digest = "SHA256")
  @key_generator = key_generator
  @digest = digest
end

def key_for(column)
  @key_generator.generate_key("Devise #{column}")
end