cal.rb

# require 'ap'

def months_between(d1, d2)
  (d2.year * 12 + d2.month) - (d1.year * 12 + d1.month)
end

today = Date.today

first = (today - 10.weeks).beginning_of_month
last = today.end_of_month

cal = {}

(first..last).each do |date|
  week_number = (date - today + today.wday).to_i / 7
  day_number = (date - today + today.wday).to_i % 7

  month = months_between(first, date)
  row = week_number + month
  col = day_number

  cal[row] ||= []
  cal[row][col] = date
end

# ap cal
(cal.keys.min..cal.keys.max).each do |row|
  days_in_week = cal[row]
  if days_in_week
    (0...7).each do |col|
      date = days_in_week[col]
      print date ? " %2d" % date.day : "   "
    end
  end

  print "\n"
end