class Fluent::ForwardOutput::FailureDetector

def add(now)
  if @window.empty?
    @window << @init_gap
    @last = now
  else
    gap = now - @last
    @window << (gap * 1e6).to_i
    @window.shift if @window.length > SAMPLE_SIZE
    @last = now
  end
end

def clear
  @window.clear
  @last = 0
end

def hard_timeout?(now)
  now - @last > @hard_timeout
end

def initialize(heartbeat_interval, hard_timeout, init_last)
  @heartbeat_interval = heartbeat_interval
  @last = init_last
  @hard_timeout = hard_timeout
  # microsec
  @init_gap = (heartbeat_interval * 1e6).to_i
  @window = [@init_gap]
end

def phi(now)
  size = @window.size
  return 0.0 if size == 0
  # Calculate weighted moving average
  mean_usec = 0
  fact = 0
  @window.each_with_index {|gap,i|
    mean_usec += gap * (1+i)
    fact += (1+i)
  }
  mean_usec = mean_usec / fact
  # Normalize arrive intervals into 1sec
  mean = (mean_usec.to_f / 1e6) - @heartbeat_interval + 1
  # Calculate phi of the phi accrual failure detector
  t = now - @last
  phi = PHI_FACTOR * t / mean
  return phi
end

def sample_size
  @window.size
end