A challenge: adding months to a date?

[David Bovill]

Does anyone know exactly what the convert is doing with the times? I
modified Kens code so it also returns the best guess date as well as working
out the month and year - that is if there is no exact match it return s the
last day of that month....

And the Unit test returns this:

Thu, 28 Feb 2002 01:00:00 +0000
Sun, 31 Mar 2002 02:00:00 +0000
Tue, 30 Apr 2002 02:00:00 +0000
Fri, 31 May 2002 02:00:00 +0000
Sun, 30 Jun 2002 02:00:00 +0000
Wed, 31 Jul 2002 02:00:00 +0000
Sat, 31 Aug 2002 02:00:00 +0000
Mon, 30 Sep 2002 02:00:00 +0000
Thu, 31 Oct 2002 01:00:00 +0000
Sat, 30 Nov 2002 01:00:00 +0000
Wed, 31 Dec 2003 01:00:00 +0000
Fri, 31 Jan 2003 01:00:00 +0000
Fri, 28 Feb 2003 01:00:00 +0000
Mon, 31 Mar 2003 02:00:00 +0000
1 2 3 4 5 6 7 8 9 10 11 12 1 2 3

Which passes - as each month is incremental, as are the month numbers. But -
why do the times change from October to February. Note I added the 2am line
to the script to ensure convert does not subtract the odd day now and
then...

Here is the modified code:

on mouseUp
    put "2002,1,31,1,0,0,5" into startDate
    put 1 into lastMonth
    put lastMonth into endMonths
    repeat with statementNumber = 1 to 14
        set the cursor to busy
        date_AddMonth statementNumber, startDate, endMonth, endYear
        put the result
        put space & endMonth after endMonths

        if statementNumber mod 12 is not (endMonth - 1) then
            put merge("Failed adding [[statementNumber]] to
[[abbeyStartDate]]. Resulted in [[someMonth]]")
        end if
    end repeat

    put endMonths
end mouseUp

on date_AddMonth monthsToAdd, startDate, @endMonth, @endYear
    -- thanks to Ken Ray <kray at sonsothunder.com> !
    put startDate into someDate

    convert someDate to dateItems
    put item 1 of someDate into tYear
    put item 2 of someDate into tMonth
    put (monthsToAdd+tMonth) mod 12 into endMonth
    if endMonth = 0 then put 12 into endMonth
    put ((monthsToAdd+tMonth) div 12) + tYear into endYear

    put endYear into item 1 of someDate
    put endMonth into item 2 of someDate
    put date_MaxDaysInMonth(endMonth, endYear) into item 3 of someDate
    put 2 into item 4 of someDate    # seems to be required !!!
    convert someDate to internet date
    return someDate
end date_AddMonth

function date_MaxDaysInMonth theMonth, theYear
    -- thanks to Björnke von Gierke <bvg at mac.com> !

    put "1,January,3,March,5,May,7,July,8,August,10,October,12,December"
into Months31
    put "4,April,6,June,9,September,11,November" into Months30
    if theMonth is among the items of Months31 then
        put 31 into HowManyDays
    else if theMonth is among the items of Months30 then
        put 30 into HowManyDays
    else --February
        if (theYear mod 400 = 0) or (theYear mod 100 <> 0) and (theYear mod
4 = 0) then
            put 29 into HowManyDays -- leap year
        else
            put 28 into HowManyDays
        end if
    end if
    return HowManyDays
end date_MaxDaysInMonth