#14704: New function to wxDateTime to get wxDateSpan
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 Reporter:  jonasr       |       Owner:    
     Type:  enhancement  |      Status:  new
 Priority:  normal       |   Milestone:    
Component:  base         |     Version:    
 Keywords:  wxDateTime   |   Blockedby:    
    Patch:  1            |    Blocking:    
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 Hi

 A new function to wxDateTime similar to
 {{{
 wxTimeSpan Subtract(const wxDateTime &dt)
 }}}
 which returns a wxDateSpan with all fields filled:
 {{{
 wxDateSpan SubtractDate(const wxDateTime &dt)
 }}}

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
-------------------------+------------------------------------------------- -
 Reporter:  jonasr       |       Owner:          
     Type:  enhancement  |      Status:  confirmed
 Priority:  normal       |   Milestone:          
Component:  base         |     Version:          
 Keywords:  wxDateTime   |   Blockedby:          
    Patch:  1            |    Blocking:          
-------------------------+------------------------------------------------- -
Changes (by vadz):

  * status:  new => confirmed

Comment:

 Thanks for your patch, I agree that this could be useful.

 But I'm not sure if `SubtractDate()` is really a good name for it, I
 really would be hard pressed to explain how is it different from just
 `Subtract()`. I can propose `SubtractLogical()` but this is not ideal
 neither so what about a longer but perfectly clear `DiffAsDateSpan()`? It
 is inconsistent with `Subtract()`, of course, but OTOH it's really a
 different operation so I think clarity is more important than consistency
 here. But any other suggestions for the name would be welcome.

 Also, and this is really important, could you please add a few tests for
 the new function to
 [source:wxWidgets/trunk/tests/datetime/datetimetest.cpp
 tests/datetime/datetimetest.cpp]? If you have trouble with this, please
 see [source:wxWidgets/trunk/docs/tech/tn0017.txt the instructions].

 TIA!

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
-------------------------+------------------------------------------------- -
 Reporter:  jonasr       |       Owner:          
     Type:  enhancement  |      Status:  confirmed
 Priority:  normal       |   Milestone:          
Component:  base         |     Version:          
 Keywords:  wxDateTime   |   Blockedby:          
    Patch:  1            |    Blocking:          
-------------------------+------------------------------------------------- -

Comment(by jonasr):

 I'll think about the name. I wanted it to be as close to Subtract as
 possible, but perhaps i'ts too close.

 As for tests, I didn't find any tests for Subtract/Add in
 datetimetest.cpp, and the size of it, and its embedded python scripts,
 scared me.
 But now that i revisit it, I realize that operator- is an alias for
 subtract, so now i feel dumb. I'll try to cook up some tests.

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
-------------------------+------------------------------------------------- -
 Reporter:  jonasr       |       Owner:          
     Type:  enhancement  |      Status:  confirmed
 Priority:  normal       |   Milestone:          
Component:  base         |     Version:          
 Keywords:  wxDateTime   |   Blockedby:          
    Patch:  1            |    Blocking:          
-------------------------+------------------------------------------------- -

Comment(by jonasr):

 Writing the test I noted that arithmetics with the resulting wxDateSpan
 gives wrong results.

 Consider this:

 {{{
 wxDateTime dt1(11, wxDateTime::Jan, 1996);
 wxDateTime dt2(5, wxDateTime::Jun, 1998);
 wxDateSpan diff = dt2.DiffAsDateSpan(dt1);
 // now diff has years=1, months=28, weeks=125, days=0
 wxDateTime dt3 = dt1 + diff;
 // now dt3 = 2001-10-02, so dt3 != dt2
 }}}

 This is because DiffAsDateSpan fills all fields that it can, so calls to
 GetYears()/GetMonths()/GetDays() etc. returns correctly for the diff.
 But wxDateSpan::Add(const wxDateSpan&) uses all fields for adding, so it
 effectivly adds the span four times.
 This maybe is somewhat unexpected, so i make a not of it in the
 documentation.

 This means that writing a test that checks arithmetics is not possible, so
 the only thing I can think of is testing that the calculation of
 year/month/week/day is correct, hope that's ok.

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
-------------------------+------------------------------------------------- -
 Reporter:  jonasr       |       Owner:          
     Type:  enhancement  |      Status:  confirmed
 Priority:  normal       |   Milestone:          
Component:  base         |     Version:          
 Keywords:  wxDateTime   |   Blockedby:          
    Patch:  1            |    Blocking:          
-------------------------+------------------------------------------------- -

Comment(by vadz):

 Err, I think the implementation is wrong then (hence the usefulness of
 writing tests!). I'd expect the operation above to give "2 years, 4
 months, 25 days", i.e. the number of months should never be greater than
 12 in `wxDateSpan`. And if it worked like this, then addition would work,
 as expected.

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
-------------------------+------------------------------------------------- -
 Reporter:  jonasr       |       Owner:          
     Type:  enhancement  |      Status:  confirmed
 Priority:  normal       |   Milestone:          
Component:  base         |     Version:          
 Keywords:  wxDateTime   |   Blockedby:          
    Patch:  1            |    Blocking:          
-------------------------+------------------------------------------------- -

Comment(by jonasr):

 For my purpose, I needed to get a span that returns the actual diff
 between two dates for each part of
 GetYears()/GetMonths()/GetWeeks()/GetDays(), so I wanted GetMonths() to
 return 28 in example above. (btw, i see it's a typo in the example, year
 in diff is ofcourse 2, not 1)

 But I guess that this is a misunderstanding/misuse of wxDateSpan, and I
 agree that arithmetics should work as expected.
 Now this function is of no use to me, but if someone else finds it useful
 I made a new patch.

 Note that for the tests to pass, and to keep with how I understand
 wxDateSpan, weeks are set, so it's not exactly like your example, but
 rather "2 years, 4 months, 3 weeks, 4 days"

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
-------------------------+------------------------------------------------- -
 Reporter:  jonasr       |       Owner:          
     Type:  enhancement  |      Status:  confirmed
 Priority:  normal       |   Milestone:          
Component:  base         |     Version:          
 Keywords:  wxDateTime   |   Blockedby:          
    Patch:  1            |    Blocking:          
-------------------------+------------------------------------------------- -

Comment(by vadz):

 I think you may want to add `wxDateSpan::GetTotalMonths()` method, just as
 already have `GetTotalDays()`. Then you should be able to get the values
 that you need. Of course, it's not exactly difficult to write
 `12*GetYears()+GetMonths()` directly neither but I wouldn't be against
 adding such method if people think it can be useful.

 In the meanwhile I'll apply this patch, thanks!

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
--------------------------+------------------------------------------------ -
  Reporter:  jonasr       |       Owner:            
      Type:  enhancement  |      Status:  closed    
  Priority:  normal       |   Milestone:            
 Component:  base         |     Version:            
Resolution:  fixed        |    Keywords:  wxDateTime
 Blockedby:               |       Patch:  1        
  Blocking:               |  
--------------------------+------------------------------------------------ -
Changes (by VZ):

  * status:  confirmed => closed
  * resolution:  => fixed

Comment:

 (In [72600]) Add wxDateTime::DiffAsDateSpan().

 This method returns the difference between the dates as wxDateSpan, unlike
 the
 existing Subtract() and overloaded operator-() that return wxTimeSpan.

 Closes #14704.

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
--------------------------+------------------------------------------------ -
  Reporter:  jonasr       |       Owner:            
      Type:  enhancement  |      Status:  reopened  
  Priority:  normal       |   Milestone:            
 Component:  base         |     Version:            
Resolution:               |    Keywords:  wxDateTime
 Blockedby:               |       Patch:  1        
  Blocking:               |  
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Changes (by jonasr):

  * status:  closed => reopened
  * resolution:  fixed =>

Comment:

 Here's a patch for {{{wxDateSpan::GetTotalMonths()}}}.

 But starting to use this function in my app, I'm embarrased to say that my
 previous patch had a couple of bugs in it. Turns out that the test I added
 were to trivial. Dates are tricky.
 Attached is a patch that fixes {{{wxDateTime::DiffAsDateSpan}}}, plus more
 extensive tests.

 Hope it's ok to add 2 patches to an old ticket like this.

 Regards
 //Jonas

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
--------------------------+------------------------------------------------ -
  Reporter:  jonasr       |       Owner:            
      Type:  enhancement  |      Status:  reopened  
  Priority:  normal       |   Milestone:            
 Component:  base         |     Version:            
Resolution:               |    Keywords:  wxDateTime
 Blockedby:               |       Patch:  1        
  Blocking:               |  
--------------------------+------------------------------------------------ -

Comment(by vadz):

 If it helps, it's rare for me to write any non trivial code working with
 dates without bugs too. The best is to generate a lot of random data
 (there are small Python scripts embedded into the test, e.g. see
 source:wxWidgets/trunk/tests/datetime/datetimetest.cpp#L383) and check
 that everything works correctly with it.

 Will apply the fixes soon, thanks again!

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
--------------------------+------------------------------------------------ -
  Reporter:  jonasr       |       Owner:            
      Type:  enhancement  |      Status:  reopened  
  Priority:  normal       |   Milestone:            
 Component:  base         |     Version:            
Resolution:               |    Keywords:  wxDateTime
 Blockedby:               |       Patch:  1        
  Blocking:               |  
--------------------------+------------------------------------------------ -

Comment(by VZ):

 (In [72615]) Add wxDateSpan::GetTotalMonths() method.

 This is similar to the existing GetTotalDays() and counts both months and
 years.

 See #14704.

#14704: New function to get difference of two wxDateTime objects as a wxDateSpan
--------------------------+------------------------------------------------ -
  Reporter:  jonasr       |       Owner:            
      Type:  enhancement  |      Status:  closed    
  Priority:  normal       |   Milestone:            
 Component:  base         |     Version:            
Resolution:  fixed        |    Keywords:  wxDateTime
 Blockedby:               |       Patch:  1        
  Blocking:               |  
--------------------------+------------------------------------------------ -
Changes (by VZ):

  * status:  reopened => closed
  * resolution:  => fixed

Comment:

 (In [72616]) Fix bugs in the recently added wxDateTime::DiffAsDateSpan().

 Correct the test for negative spans less than a month and use the correct
 month for computing the number of days in it.

 Also add unit tests for problematic cases.

 Closes #14704.