#for RubyPico (mruby)

#mrubyには String#center がないので適当に実装
class String
  def center(n)
    i = (n - length).div(2)
    " " * i + self + " " * (n - i - length)
  end
end

month_table = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

#うるう年か？
is_uruu = ->(year) {
  (year % 4 == 0 and year % 100 != 0) or year % 400 == 0
}

#西暦1年1月1日から何日目か（すべてグレゴリオ暦で計算）
days = ->(year, month, day) {
  uruu = ->(y) {
    y.div(4) - y.div(100) + y.div(400)
  }
  month_days = ->(mth) {
    month_table[0, mth].inject(&:+) + (is_uruu[year] && mth > 2 ? 1 : 0)
  }
  y1 = year - 1
  y1 * 365 + uruu[y1] + month_days[month] + day - 1
}

#曜日の計算
week_number = ->(year, month, day) {
  (days[year, month, day] + 1) % 7
}

#カレンダーの出力
Calender = ->(year, month) {
  gen = ->(from, to) {
    st = ""
    from.upto(to) do |i|
      st += sprintf("%2d  ", i)
      st = st[0..-2] if i < 10    #mrubyのバグ？　とりあえずパッチ。
    end
    st
  }
  putout = ->(i) {
    last = month_table[month]
    last += 1 if is_uruu[year] and month == 2
    while i + 6 <= last
      puts gen[i, i + 6]
      i += 7
    end
    st = gen[i, last]
    puts st unless st.empty?
  }
  puts "#{year}/#{month}".center(27)
  puts "sun mon tue wed thu fri sat"
  w = week_number[year, month, 1]
  puts "    " * w + gen[1, 7 - w]
  putout[8 - w]
}

year, month = Popup.input("年と月を入力して下さい（スペースで区切る）").split.map(&:to_i)
Calender[year, month]