librato_metric.rb

require 'lazy'
require 'system_timer'

class LibratoMetric
  COUNT      = 10
  RESOLUTION = 1

  def initialize(metric_name, timeout = 5)
    @metric_name = metric_name
    @timeout     = timeout

    # Start loading data
    data
  end

  def data
    @data ||= Lazy.future do
      with_timeout { Librato::Metrics.fetch(@metric_name, :count => COUNT, :resolution => RESOLUTION, :summarize_time => true) }
    end
  end

  def value
    @value ||= Lazy.demand(data).sum { |source, data| data[0]['value'] }
  end

  def time
    measure_time + COUNT.minutes
  end

  def measure_time
    @measure_time ||= Time.at(Lazy.demand(data).collect { |source, data| data[0]['measure_time'] }.min)
  end

  def with_timeout(&block)
    SystemTimer.timeout_after(@timeout, Timeout::Error, &block)
  end
end