January not shown for some years in en_GB

[percysnoodle]

I have a calendar view which I set up like so:

        _calendarView = [[TSQCalendarView alloc] init];
        _calendarView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
        _calendarView.delegate = self;
        _calendarView.rowCellClass = [C3CCalendarRowCell class];
        _calendarView.pagingEnabled = YES;
        _calendarView.firstDate = [NSDate dateWithTimeIntervalSince1970:0];
        _calendarView.lastDate = [NSDate dateWithTimeIntervalSince1970:(36525 + 364) * kSecondsInADay];
        _calendarView.selectedDate = selectedDate;
        [self.contentView addSubview:_calendarView];

C3CCalendarRowCell just defines some images, as per the example app. When I scroll to the start of 2010, I see this:

Looking in the debugger, I see that something weird is going in inside -[tableView:numberOfRowsInSection:]. firstWeek is 3, but nextToLastWeek is 53, so that section has minus 47 rows.

Could this be because my calendar locale is en_GB? It's possible we have different rules about week numbers in Britain; I have no idea.

[percysnoodle]

Looking further into this, it also affects 2011 and 2012, but not 2009 or 2008. Not sure what makes them different.

I notice there's a comment in the code:

    // -[NSDateComponents weekOfYear] doesn't explicitly specify what its valid range is. In the Gregorian case, it appears to be [1,52], which means the last day of December is probably going to be week 1 of next year. The same logic extends to other calendars.

so I added this code to -[tableView:numberOfRowsInSection:] to test out the range methods on NSCalendar:

    if ((section == 480) || (section == 504))
    {
        NSLog(@"section %d", section);
        NSLog(@"firstWeek %d", firstWeek);
        NSLog(@"nextToLastWeek %d", nextToLastWeek);
        NSRange range;

        range = [self.calendar minimumRangeOfUnit:NSWeekOfYearCalendarUnit];
        NSLog(@"minimumRangeOfUnit:[%d, %d]", range.location, range.location + range.length - 1);

        range = [self.calendar maximumRangeOfUnit:NSWeekOfYearCalendarUnit];
        NSLog(@"maximumRangeOfUnit:[%d, %d]", range.location, range.location + range.length - 1);

        range = [self.calendar rangeOfUnit:NSWeekOfYearCalendarUnit inUnit:NSYearCalendarUnit forDate:firstOfMonth];
        NSLog(@"rangeOfUnit:inUnit:[%d, %d]", range.location, range.location + range.length - 1);
    }

I got this output:

2013-03-16 18:42:31.324 MyApp[95353:c07] section 480
2013-03-16 18:42:31.324 MyApp[95353:c07] firstWeek 53
2013-03-16 18:42:31.324 MyApp[95353:c07] nextToLastWeek 3
2013-03-16 18:42:31.324 MyApp[95353:c07] minimumRangeOfUnit:[1, 52]
2013-03-16 18:42:31.324 MyApp[95353:c07] maximumRangeOfUnit:[1, 53]
2013-03-16 18:42:31.324 MyApp[95353:c07] rangeOfUnit:inUnit:[0, 52]
2013-03-16 18:42:31.325 MyApp[95353:c07] section 504
2013-03-16 18:42:31.326 MyApp[95353:c07] firstWeek 52
2013-03-16 18:42:31.326 MyApp[95353:c07] nextToLastWeek 4
2013-03-16 18:42:31.326 MyApp[95353:c07] minimumRangeOfUnit:[1, 52]
2013-03-16 18:42:31.326 MyApp[95353:c07] maximumRangeOfUnit:[1, 53]
2013-03-16 18:42:31.326 MyApp[95353:c07] rangeOfUnit:inUnit:[0, 53]

Hopefully that's useful in figuring out the valid range. I also found that I can work around the problem by adding this just before the return:

    if (firstWeek > nextToLastWeek)
    {
        // The first week must have been the end of last year.
        firstWeek = 0;
    }

but I'm not sure I understand what I've done well enough to say that that's fixed the problem. I could still put it in a pull request, if you'd like (I've signed the CLA for KIF - do I need to sign it again for TS?).