module Locksmith
  extend self

  Locked = Class.new(StandardError)

  def acquire(page, user, timeout = 30)
    if key[page.id].setnx(user.id)
      key[page.id].expire(timeout)
    else
      raise Locked
    end
  end

  def release(page)
    key[page.id].del
  end

  def key
    Nest.new(:Locksmith)
  end
end