nth week

gistfile1.rb

def nthweek( time )
    time.strftime("%U").to_i
end

def get_time_by_nthweek(i, year = Time.now.year)
    first_day = Time.mktime(year,1,1)
    first_day - first_day.wday.days + i*7.days
end

def next_nthweek(i, year = Time.now.year)
    time = get_time_by_nthweek(i, year) + 7.days
    return time.year, nthweek( time )
end

def previous_nthweek(i, year = Time.now.year)
    time = get_time_by_nthweek(i, year) - 7.days
    return time.year, nthweek( time )
end

# example
foo = nthweek( Time.parse('2009-01-01') ) # 0
bar = get_time_by_nthweek(foo) # 2008-12-28

foo = nthweek( Time.parse('2009-01-14') ) # 2
bar = get_time_by_nthweek(foo) # 2009-1-11

year, nthweek = next_nthweek(52, 2008)  # 2009, 1
year, nthweek = previous_nthweek(1, 2009) # 2008, 52