week_field gives wrong week after serialization and deserialization - ruby-on-rails

Question

I'm using the week_field helper to generate a week picker in a form. When I choose a week and submit, my controller gets the correct serialized week (e.g. '2014-W03') which I can turn into a date object. That all works, but when the date is serialized again it is always decremented by 1 (e.g. it'll be '2014-W02'). I looked at the source code for the week_field helper and it serializes as
def format_date(value)
value.try(:strftime, "%Y-W%W")
end
but this doesn't seem to be the encoding when the date is parsed. Furthermore, parsing and then serializing a date yeilded this wonky result:
irb > Date.parse('2014-W03').strftime('%Y-W%W')
=> "2014-W02"
Any ideas as to what's going on here or how I can do this in a way that makes sense? I'd hate to have an extra +1 on the week number or change the week_field format_date definition if there's a cleaner route.

Answer 1

This is from http://apidock.com/ruby/DateTime/strftime :
%W - Week number of the year. The week starts with Monday. (00..53)
It seems you have the good old - start with 0 or start with 1 - problem. Strftime will start counting weeks with 0.
But maybe %V is the right thing for you:
ISO 8601 week-based year and week number:
The week 1 of YYYY starts with a Monday and includes YYYY-01-04.
The days in the year before the first week are in the last week of
the previous year.
%G - The week-based year
%g - The last 2 digits of the week-based year (00..99)
%V - Week number of the week-based year (01..53)