eta.rb

# ETA class is used to calculate the time a script will finish
# It needs to be initilized with the total number of units to be processed
# It needs to be called with the current number of of units processed so far
# eg:   eta = Eta.new(things.count)
#       things.each_with_index do |thing, index|
#          puts eta.calc(index) rescue nil
#          do_something(thing)
#       end
# eta goes first because on index 0 you've processed 0 units
# Usage:
#  Eta.new(total, start_time, note, frequency)
#  total: total number of units to iterate over
#  start_time: time the first unit started to process
#  note: a string to include in the output (helpfull if you have more than 1 eta at a time)
#  frequency: sampeling frequency, default should produce 100 lines of output
#    eg: frequency of 3 would give results every third index
class Eta

  attr_accessor :total, :start_time, :note, :frequency, :index, :display_memory_usage

  def initialize(t, st = Time.now, n = nil, f = [t/100, 1].max)
    @total = t
    @start_time = st
    @note = n
    @frequency = f
    @index = 0
    @display_memory_usage = false
  end

  def calc(idx = nil)
    #TODO: Cleanup instance variable associations, remove total = @total lines
    n = "#{note.to_s} (Mem: #{NewRelic::Agent::Samplers::MemorySampler.new.sampler.get_sample.to_i}M)" if display_memory_usage
    idx ||= @index += 1
    
    if idx > 1 && idx % frequency != 0
      return 
    end
    
    if idx == 1
      return "working #{idx} of #{total}%s." % (" #{n}" if n)
    elsif idx > total
      return "working #{idx} of #{total}%s. Should be done already." % (" #{n}" if n)
    else
      rate = (idx / (Time.now - start_time))
      ttf = (total - idx) / rate
      eta = (Time.now + ttf.round.seconds).strftime("%Y-%m-%d %H:%M:%S")

      seconds    =  ttf % 60
      ttf = (ttf - seconds) / 60
      minutes    =  ttf % 60
      ttf = (ttf - minutes) / 60
      hours      =  ttf 

      return "working #{idx} of #{total}%s. ETA: #{eta} (%02d:%02d:%02d)" % [(" #{n}" if n), hours, minutes, seconds]
    end
  end

  def out(idx = nil)
    begin
      output = self.calc(idx)
      puts output unless output.nil? 
    rescue => e
      puts "eta error: " + e.full_message
    end
  end

end