progress.rb

class Progress
  class DefaultFormatter
    def progress_format(current, total)
      format("\e[K\e[G %5.2f%% (%s / %s)", current / total.to_f * 100.0, format_number(current), format_number(total))
    end

    def format_number(number)
      number.to_s.chars.reverse.each_slice(3).map(&:reverse).reverse.map(&:join).join(" ")
    end
  end

  UPDATE_FREQUENCY = 0.01

  attr_accessor :current
  attr_reader :total

  def initialize(total, formatter: DefaultFormatter.new, out: $stdout)
    @out = out
    @current = 0
    @total = total
    @formatter = formatter
    @last_print_at = nil

    if block_given?
      @out.print "\e[?25l"

      begin
        yield self
      ensure
        @out.puts "\e[?25h"
      end
    end
  end

  def print
    return unless should_print?

    @last_print_at = Time.now

    @out.print @formatter.progress_format(@current.succ, @total)
    @out.flush
  end

  private

  def should_print?
    return true unless @last_print_at
    return true if Time.now - @last_print_at > UPDATE_FREQUENCY
    return true if @current.succ >= @total
    false
  end
end

count = 10_000_000

Progress.new(count) do |progress|
  count.times do |i|
    progress.current = i
    progress.print
    sleep Math.sin(i * 3000).abs * 0.000001
  end
end