plain_time.rb

class PlainTime
  include Comparable

  attr_reader :hour, :minute, :second

  HOUR_PER_DAY = 24
  MINUTE_PER_HOUR = 60
  SECOND_PER_MINUTE = 60

  SECOND_PER_HOUR = HOUR_PER_DAY * MINUTE_PER_HOUR

  def initialize(hour, minute, second)
    @hour = hour.tap { |h| raise ArgumentError, "hour is #{h}" if h > HOUR_PER_DAY }
    @minute = minute.tap { |m| raise ArgumentError, "minute is #{m}" if m > MINUTE_PER_HOUR }
    @second = second.tap { |s| raise ArgumentError, "second is #{s}" if s > SECOND_PER_MINUTE }
  end

  def self.from_second(input_in_second)
    hour = input_in_second / SECOND_PER_HOUR
    minute = (input_in_second - hour * SECOND_PER_HOUR) / MINUTE_PER_HOUR
    second = (input_in_second - hour * SECOND_PER_HOUR - minute * MINUTE_PER_HOUR)

    new(hour, minute, second)
  end

  def am?
    hour < 12
  end

  def pm?
    !am?
  end

  def on(date)
    Time.local(date.year, date.month, date.day, hour, minute, second)
  end

  def +(other)
    PlainTime.from_second(self.to_i + other.to_i)
  end

  def <=>(other)
    if hour != other.hour
      hour <=> other.hour
    elsif minute != other.minute
      minute <=> other.minute
    elsif second != other.second
      second <=> other.second
    else
      0
    end
  end

  def in_seconds
    (hour * SECOND_PER_HOUR) + (minute * SECOND_PER_MINUTE) + second
  end

  alias to_i in_seconds

  def inspect
    format(
      '%02d:%02d:%02d %s',
      hour,
      minute,
      second,
      pm? ? 'PM' : 'AM'
    )
  end

  alias to_s inspect
end