Ruby token bucket rate limiter

class TokenBucket
  def initialize(rate:, burst:, clock: -> { Process.clock_gettime(Process::CLOCK_MONOTONIC) })
    @rate = Float(rate)
    @burst = Float(burst)
    @clock = clock
    @tokens = @burst
    @stamp = @clock.call
  end

  def allow?(cost = 1.0)
    now = @clock.call
    @tokens = [@burst, @tokens + (now - @stamp) * @rate].min
    @stamp = now
    return false if @tokens < cost
    @tokens -= cost
    true
  end
end