From: Rick DeNatale <rick.denatale@...>
Date: 2010-04-30T00:53:43+09:00
Subject: Re: Handling week numbers according to US Standard and ISO 8601

On Wed, Apr 28, 2010 at 4:58 PM, Kasper Tidemann <kaspert@gmail.com> wrote:
> Hi ruby-lang list,
>
> Thank you all for reading this mail.
>
> I am struggling to handle week numbers properly on a web platform made in
> Ruby that is used across several countries. I have googled this for days
> trying to find a solution, but I have not had any success whatsoever so far.
>
> The problem is the following:
>
> ------- DENMARK:
>
> 1) Say we are using the system in Denmark and we want to know the week
> number of the date 2009-12-31.
>
> 2) Denmark follows the ISO 8601 standard for calendar handling, and the
> server running the system is initialized using the Europe/Copenhagen time
> zone.
>
> 3) Executing Date.civil(2009, 12, 31).cweek returns "53", which is the
> correct answer, since December 31st 2009 is part of week 53 in Denmark (and
> the rest of Europe, pretty much).
>
> ------- USA:
>
> 1) Now we are using the system in USA, but still communicating with the same
> server here in Denmark, the UI itself just speaks English.
>
> 2) When I execute Date.civil(2009, 12, 31).cweek, it still - obviously -
> returns "53". But in the case of USA, this is wrong, since December 31st
> 2009 would be week 52 according to the US Standard.
>
> -------
>
> Now, I have tried to use TZInfo for Ruby, doing a
> Time.zone.parse("2009-12-31").strftime("%W") to get the week number of
> December 31st 2009 - with weeks beginning on Monday (ISO 8601). This returns
> 52, which is WRONG according to European standards.
>
> However, executing Time.zone.parse("2009-12-31").strftime("%U") to get the
> week number of December 31st 2009 - with weeks beginning on Sunday (US
> Standard) - returns 52. Which is right.
>
> So, I have Date.civil that tells me one thing - 53 - and Time.zone that
> tells me another - 52. Either is wrong in one of the cases.
>
> Do you guys have any ideas regarding handling the week numbers correctly
> according to the country of the user? Is there a way to tell Date.civil() to
> follow a specific standard, or does it just inherit from the machine
> settings no matter what? What can I do to fix this?
>
> Thank you for your help.
>
> All the best,
> Kasper Tidemann
> kaspert@gmail.com

My ri_cal gem (whose purpose is to support rfc2445/5545 icalendar
data) extends Time and DateTime with this method

        # return the iso year of the receiver
        # == parameter
        # wkst:: an integer representing the day of the week on which
weeks are deemed to start. This uses
        # the ruby convention where 0 represents Sunday.
        def iso_year(wkst)


http://github.com/rubyredrick/ri_cal
-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Github: http://github.com/rubyredrick
Twitter: @RickDeNatale
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