Countdown (with output always shown at the top of the terminal)

countdown.rb

class Countdown
  BELL = "\a"
  COLORS = { 
    'black'   => 30,
    'red'     => 31, 
    'green'   => 32, 
    'yellow'  => 33,
    'blue'    => 34,
    'magenta' => 35,
    'cyan'    => 36,
    'white'   => 37
  }

  def self.for total_time_in_minutes
    total_time_in_seconds = total_time_in_minutes * 60
    end_time =  Time.now + total_time_in_seconds

    print choose_color(total_time_in_seconds, total_time_in_seconds) + format_time(total_time_in_seconds)
    print fill

    while Time.now < end_time
      time_remaining = end_time - Time.now
      print backtrack
      print choose_color(total_time_in_seconds, time_remaining) + format_time(time_remaining)
      print fill
      sleep 1
    end
    print backtrack
    puts "\e[#{COLORS['blue']}mDone!" + BELL
  end

  private

  def self.terminal_height
    `tput lines`.to_i
  end

  def self.backtrack
     "\e[#{terminal_height}A" + " " * 8 + "\e[#{8}D"
  end

  def self.fill
    output = ""
    (terminal_height - 1).times do
      output <<  "\n"
    end
    output
  end

  def self.format_time time
    seconds = time % 60
    minutes  = (time / 60) % 60
    hours = time / 3600
    formatted_string = sprintf("%02d:%02d:%02d", hours, minutes, seconds);
  end

  def self.choose_color total_time_in_seconds, seconds_remaining
    percentage_remaining = 100 * seconds_remaining / total_time_in_seconds
    if percentage_remaining < 5
      color_code = COLORS['red']
    elsif percentage_remaining < 10
      color_code = COLORS['yellow']
    else
      color_code = COLORS['green']
    end
    "\e[#{color_code}m"
  end
end