Date_calc

> irb
> require './datecalc'

irb(main):002> dc = DateCalc.new('2026-05-25')
irb(main):003> dc.w + 5 # advance 5 weeks
irb(main):005> puts dc # '2026-06-29' 

→MS # advance to next Summer Soltice (or stay if condition is met)
→SE→FM→Thu # advance to next Summer Equinox,
#            then to next Full Moon, then to next Thursday

dc = DateCalc.new               # 2026-05-27
dc.m + 5                        # => #<DateCalc …>  (date advanced 5 months)
puts dc                         # 2026-10-27
puts dc.m                       # 10  (read the new value via to_s)

dc.d - 10                       # => #<DateCalc …>  (back 10 days)
puts dc                         # 2026-10-17

dc.y + 1                        # => #<DateCalc …>
puts dc                         # 2027-10-17

# chaining works
(dc.y + 1).m + 2                # advance year by 1, then months by 2