Very simple Date math goes randomly bonkers

[Matt Darby]

I have a "timesheet" in my app that simply displays the week range
based on a passed in date (params[:date]).
The view iterates through the Date::ABBR_DAYNAMES and shows a link to
the corresponding date.

Trouble is that about 40% of the time the calculated dates go bonkers.
Am I missing something?

Model:
# Get a date range of the week that a particular date falls in
# This is broken out like mad for diagnostics
def self.get_work_week_date_range(date)
monday = date.monday
sunday = monday - 1.day
eow = date.end_of_week
saturday = eow - 1.day

dates = [sunday, saturday]

logger.info
(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>")
logger.info(">>>>> #{date}.monday = #{monday}")
logger.info(">>>>> #{monday}-1.day = #{sunday}")
logger.info(">>>>> #{date}.end_of_week = #{eow}")
logger.info(">>>>> #{eow}-1.day = #{saturday}")
logger.info(">>>>> #{date} == [#{dates[0]}, #{dates[1]}]")
logger.info
(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>")

dates
end

Logger output:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>> 2008-12-08.monday = 2008-12-08
>>>>> 2008-12-08-1.day = 2008-12-07
>>>>> 2008-12-08.end_of_week = 2008-12-14
>>>>> 2008-12-14-1.day = 2008-12-13
>>>>> 2008-12-08 == [2008-12-07, 2008-12-13]
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

... n times later ...

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>> 2008-12-08.monday = 2008-12-08
>>>>> 2008-12-08-1.day = 1772-05-19
>>>>> 2008-12-08.end_of_week = 3428-04-08
>>>>> 3428-04-08-1.day = 3191-09-18
>>>>> 2008-12-08 == [1772-05-19, 3191-09-18]
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

[Philip Hallstrom]

On Dec 8, 2008, at 10:55 AM, Matt Darby wrote:

>
> I have a "timesheet" in my app that simply displays the week range
> based on a passed in date (params[:date]).
> The view iterates through the Date::ABBR_DAYNAMES and shows a link to
> the corresponding date.

What do you pass to get_work_week_date_range? Is it a string? Or an
instance of Date? Or Time?

If it worked once it should always work. Which suggests that maybe
you're passing in something different from time to time? One time a
Date, one time a Time?

Maybe?

Put together a test and explicitly pass the *same* argument (class and
value) and see if you can duplicate it.

[Matt Darby]

> What do you pass to get_work_week_date_range?  Is it a string?  Or an  
> instance of Date?  Or Time?

I pull the date in from the params hash, and immediately parse it to a
Date:
Date.parse(params[:date]) rescue Date.today

> If it worked once it should always work.  Which suggests that maybe  
> you're passing in something different from time to time?  One time a  
> Date, one time a Time?

You're right, that's why I've pounded my head against the wall for a
week!
This method is only called from one other method, and I've extracted
it really only for testing.

> Put together a test and explicitly pass the *same* argument (class and  
> value) and see if you can duplicate it.

All tests pass :(

it "should know how to get the week based on a date" do
TimeCard.get_work_week_date_range(Date.parse("2008-08-05")).should
== [Date.parse("2008-08-03"), Date.parse("2008-08-09")]
TimeCard.get_work_week_date_range(Date.parse("2008-01-01")).should
== [Date.parse("2007-12-30"), Date.parse("2008-01-05")]
TimeCard.get_work_week_date_range(Date.parse("2008-02-29")).should
== [Date.parse("2008-02-24"), Date.parse("2008-03-01")]
TimeCard.get_work_week_date_range(Date.parse("2007-02-28")).should
== [Date.parse("2007-02-25"), Date.parse("2007-03-03")]
end

[Frederick Cheung]

On Dec 8, 6:55 pm, Matt Darby <m...@matt-darby.com> wrote:

>
>
> >>>>> 2008-12-08.monday = 2008-12-08
> >>>>> 2008-12-08-1.day = 2008-12-07
> >>>>> 2008-12-08.end_of_week = 2008-12-14
> >>>>> 2008-12-14-1.day = 2008-12-13
> >>>>> 2008-12-08 == [2008-12-07, 2008-12-13]
>
> ... n times later ...
>
>
>
> >>>>> 2008-12-08.monday = 2008-12-08
> >>>>> 2008-12-08-1.day = 1772-05-19
> >>>>> 2008-12-08.end_of_week = 3428-04-08
> >>>>> 3428-04-08-1.day = 3191-09-18
> >>>>> 2008-12-08 == [1772-05-19, 3191-09-18]

Perhaps the key thing to note is that 1772-05-19 is about 236 years
and 7 months ago, which (get your calculators out) is about 86400, ie
the number of seconds in a day. Whereas on an instance of Time, +/- 1
means +/- 1 second, on instances of Date/DateTime +/- means +/- 1
second. That is I suspect the basic problem.

On newer versions of rails, things like 1.day are smart enough to do
the right thing whether or not you add a date or a Time to them (the +
method on Date is overriden to check if the argument is a thing like
1.day).
Somewhere this has gone wrong. If you have any plugins that mess with
dates (or if you've being doing stuff like that yourself) then I'd
have a look at those - it could be something like once some random
model is loaded some extensions to Date are pulled in at that point
and from then onwards calculations are borked.

Fred

[Matt Darby]

> Perhaps the key thing to note is that 1772-05-19 is about 236 years
> and 7 months ago, which (get your calculators out) is about 86400, ie
> the number of seconds in a day. Whereas on an instance of Time, +/- 1
> means +/- 1 second, on instances of Date/DateTime +/- means +/- 1
> second. That is I suspect the basic problem.

Man, good call.

> On newer versions of rails, things like 1.day are smart enough to do
> the right thing whether or not you add a date or a Time to them (the +
> method on Date is overriden to check if the argument is a thing like
> 1.day).

I'm using 2.2.2, but...

> Somewhere this has gone wrong. If you have any plugins that mess with
> dates (or if you've being doing stuff like that yourself) then I'd
> have a look at those - it could be something like once some random
> model is loaded some extensions to Date are pulled in at that point
> and from then onwards calculations are borked.

... I do monkeypatch Date, but I ensured that I wasn't actually
overriding any existing method.

Thanks for you help Fred, this smells like the right track.

[Matt Darby]

It was the facets/time library. It was loaded in a totally separate
part of the app, in a method that had not much to do with anything.

Thanks again Frederick; that one got your a WWR recommendation ;)