Get relative time in the past (with a shorter output option)

relative-past-time.rb

class RelativeTime
  MINUTE = 60
  HOUR = 60 * MINUTE
  DAY = 24 * HOUR
  WEEK = 7 * DAY
  MONTH = 4 * WEEK
  YEAR = 12 * MONTH

  def self.for(date_to, date_from = Time.zone.now, short: false)
    diff = (date_from.to_time - date_to.to_time).round
    str = "#{verb_agreement(resolution(diff))} ago"

    if short
      str = str.gsub('years', 'y').gsub('months', 'mo').gsub('weeks', 'w')
      str = str.gsub('days', 'd').gsub('hours', 'h').gsub('minutes', 'm')
      str = str.gsub('seconds', 's').gsub('an hour', 'h').gsub('a ', '1')
      str = str.gsub('ago', '').gsub(' ', '')
    end

    str
  end

  def self.resolution(diff)
    if diff >= YEAR * 2
      [(diff / YEAR).round, 'years']
    elsif diff >= MONTH * 2
      [(diff / MONTH).round, 'months']
    elsif diff >= WEEK * 2
      [(diff / WEEK).round, 'weeks']
    elsif diff >= DAY * 2
      [(diff / DAY).round, 'days']
    elsif diff >= HOUR * 2
      [(diff / HOUR).round, 'hours']
    elsif diff >= MINUTE * 2
      [(diff / MINUTE).round, 'minutes']
    else
      [diff.round, 'seconds']
    end
  end

  def self.verb_agreement(resolution)
    if resolution[0] == 1 && resolution.last == 'hours'
      'an hour'
    elsif resolution[0] == 1
      "a #{resolution.last[0...-1]}"
    else
      resolution.join(' ')
    end
  end
end