Weekday calculation doing something wrong?

[Alex9779]

Hi, I have a problem when doing calculation with weeks and weekdays when you you library and I am not able to track down why. I did a test:

NSDate *now = [NSDate date];
expectedDate = [NSDate mt_dateFromYear:[now mt_year]
                                  week:[now mt_weekOfYear]
                               weekday:[now mt_weekdayOfWeek]
                                  hour:[now mt_hourOfDay]
                                minute:[now mt_minuteOfHour]];

From what I feel expectedDate should be the same as today but it is yesterday. Maybe I have to add that I am in Europe and when I debug I can see the error: [now mt_weekdayOfWeek] returns 3 for wednesday as if 1 is monday but 3 is tuesday when sunday is 1. So the function returns one day less and recreating it with the value seems to use sunday as 1 so I get tuesday in the result, not wednesday. I dunno how to fix this or why it is this way or what I should have to set to get the correct result.

Regards, Alexander

[atomkirk]

Can I see a concrete example of how you're using these methods in a real app?

[Alex9779]

Ahh well I tried to simplify my current method because it is not very nice so I included your lib. Unfortunately I didn't save my tries. What I am trying to do is I have a date in the past and I want to calculate a new date by adding a number of weeks to the date now but I want to keep the weekday, hour and minute of the date in the past. E. g. I have 2014-02-04 15:50:00, today is 2014-02-05 22:00:00 and I wanna add 2 weeks. My expected result is 2014-02-18 15:50:00 but with the current implementation I get 2014-02-17 15:50:00. What I tried is not much different from what I wrote in my first post but I add 2 to the week component and take the year from the now date and the weekday of the original date, but as I told the function that gets the weeks day gets it with 1=monday, in this case the result is 2, and the function that creates the new day uses 1=sunday, so the constructed date has monday as weekday...

[Alex9779]

Ok here some code:

self.dueDate = [NSDate mt_dateFromYear:[now mt_year]
                                  week:[now mt_weekOfYear] + self.intervalAmount
                               weekday:[self.dueDate mt_weekdayOfWeek]
                                  hour:[self.dueDate mt_hourOfDay]
                                minute:[self.dueDate mt_minuteOfHour]];

dueDate is some date in the past, now is [NSDate date].

And here the code of my test:

expectedDate = [NSDate mt_dateFromYear:[now mt_year]
                                  week:[now mt_weekOfYear] + 2
                               weekday:[[task dueDate] mt_weekdayOfWeek]
                                  hour:[[task dueDate] mt_hourOfDay]
                                minute:[[task dueDate] mt_minuteOfHour]];

now is again [NSDate date], [task dueDate] is some date in the past...

[Alex9779]

Some time passed and I tried myself some things. I wrote a test in the test suite:

NSDate *now = [[NSDate date] mt_startOfCurrentMinute];
NSDate *expectedDate = [NSDate mt_dateFromYear:[now mt_year]
                                          week:[now mt_weekOfYear]
                                       weekday:[now mt_weekdayOfWeek]
                                          hour:[now mt_hourOfDay]
                                        minute:[now mt_minuteOfHour]];

STAssertEqualObjects(now, expectedDate, nil);

and found that with no changes the test passes. But your tests set the default to local "en_US" and so the resulting calendar object has 1 as first weekday. I am located in Germany with the local "de_DE" and our first weekday is 2, monday. So when I use:

[NSDate mt_setFirstDayOfWeek:2];

in the test the test fails. I tracked it down and it seems to me that there is some calculation error in the calendar methods "- (NSUInteger)ordinalityOfUnit:(NSCalendarUnit)smaller inUnit:(NSCalendarUnit)larger forDate:(NSDate )date" and "- (NSDate )dateFromComponents:(NSDateComponents *)comps". The first one is used to get the weekday in "- (NSUInteger)mt_weekdayOfWeek" the second one when creating the new date from the components. The first one returns a number of the weekday always based on 1=sunday, 2=monday and so on. But the second one uses the set first weekday as 1. So when you do "[NSDate mt_setFirstDayOfWeek:2];" you have to construct with 1=monday, 2=tuesday and so on. I tried with other first weekdays and the test always fails if I do not first day of week to 1.

So I think there should be a correction in "- (NSUInteger)mt_weekdayOfWeek" as follows:

weekdayOfWeek += [[NSDate mt_calendar] firstWeekday] - 1;

This will correct the return value by the difference of the set first weekday and the test will always succeed...

Regards, Alexander

[Alex9779]

After the fix from the previous post I tried to run all other test and realized a failure in "- (NSDate )mt_startOfCurrentWeek" Because we get now alway the "normalized" weekday back from "- (NSUInteger)mt_weekdayOfWeek" there has to be another fix in "- (NSDate )mt_startOfCurrentWeek":

NSDate *date = [self mt_dateDaysAfter:-(weekday - [[NSDate mt_calendar] firstWeekday])];

After that all tests succeed...

[Alex9779]

I am preparing a pull request...

[atomkirk]

Nice catch! Yeah if you make changes to the code, write new tests that pass without modifying the other tests, ill merge it right in and push a new version of the cocoapod— Sent from Mailbox for iPhone

On Sat, Feb 15, 2014 at 9:48 AM, Alexander Leisentritt notifications@github.com wrote:

I am preparing a pull request...

Reply to this email directly or view it on GitHub: https://github.com/mysterioustrousers/MTDates/issues/36#issuecomment-35160765