superiorlu/unicorn_metrics

module UnicornMetrics
  # UnicornMetrics::Timer keeps track of total time and the count of 'ticks'
  # A simple rate of average of ticks over time elapsed can be calculated this way.
  # For more advanced metrics (e.g., 1/5/15min moving averages) this data should be reported to an intelligent metric store (i.e. Graphite)
  #
  class Timer
    extend Forwardable

    attr_reader :name

    # The Raindrops::Struct can only hold unsigned long ints (0 -> 4,294,967,295)
    # Since we usually care about ms in a web application, \
    # let's store 3 significant digits after the decimal
    EXPONENT = -3

    class Stats < Raindrops::Struct.new(:count, :mantissa, :consume); end

    def_instance_delegators :@stats, :mantissa, :count, :consume

    # @param name [String] user-defined name
    def initialize(name)
      @name  = name
      @stats = Stats.new
    end

    def type
      'timer'
    end

    # @param elapsed_time [Numeric] in seconds
    def tick(elapsed_time)
      elapsed_time = (elapsed_time * 10**-EXPONENT).to_i

      @stats.mantissa = mantissa + elapsed_time
      @stats.incr_count
      @stats.consume = elapsed_time
    end

    # Reset the timer
    def reset
      @stats.mantissa = 0
      @stats.count = 0
    end

    # @return [Numeric] total elapsed time
    def sum
      (mantissa * 10**EXPONENT).to_f.round(-EXPONENT)
    end

    # @return [Hash] JSON representation of the object
    def as_json(*)
      {
        name.to_sym => {
          type: type,
          sum:  sum,
          times: count,
          consume: consume
        }
      }
    end
  end
end