XPath - find upcoming birthdays - xpath

Question

How can I find contacts with upcoming birthdays, say within 10 days, given the following XML?
<contacts>
<contact>
<name>bob</name>
<birthday>1978-05-06</birthday>
</contact>
<contact>
<name>mary</name>
<birthday>1955-06-06</birthday>
</contact>
<contact>
<name>john</name>
<birthday>1998-05-06</birthday>
</contact>
</contacts>
I've got the following xpath but it breaks down because the month-from-dateTime returns an integer (5) instead of a '0' padded string (05). Is there a way to build a date in Xpath that will accept integer parameter for day, month, year instead of my ungly hack concatenating strings?
/contacts/contact[days-from-duration(xs:dateTime(concat(year-from-dateTime(current-date()),'-',month-from-dateTime(xs:dateTime(birthday)),'-',day-from-dateTime(xs:dateTime(birthday)))) - current-date()) < 10]

Answer 1

You can use a yearMonthDuration to add so enough years to move the date to the current year:
/contacts/contact[
xs:dateTime(birthday) + xs:yearMonthDuration("P1Y") * (year-from-dateTime(current-date()) - year-from-dateTime(xs:dateTime(birthday))) < current-date() + xs:dayTimeDuration("P10D")
]
And to check that the birthday is not in the past (for works like let to avoid typing it all twice here):
/contacts/contact[
for $thisYearBirthDay in xs:dateTime(birthday) + xs:yearMonthDuration("P1Y") * (year-from-dateTime(current-date()) - year-from-dateTime(xs:dateTime(birthday)))
return $thisYearBirthDay >= current-date() and $thisYearBirthDay < current-date() + xs:dayTimeDuration("P10D")
]
However, to actually make it work, you need to check the current and the next year, in case the current-date is around xmas, e.g.:
/contacts/contact[
exists((for $delta in (0, 1) return xs:dateTime(birthday) + xs:yearMonthDuration("P1Y") * ($delta + year-from-dateTime(current-date()) - year-from-dateTime(xs:dateTime(birthday))))[. >= current-date() and . < current-date() + xs:dayTimeDuration("P10D")])
]