[xsl] date formatting function

[Bruce D'Arcus <bdarcus@xxxxxxxxxxxxx>]

I'm about to integrate the configuration code that Wendell helped me 
out with last week, but I'd like to work out one detail related to date 
formatting before doing so.

My configuration file currently has code like this for specifying date 
formatting:

	<date>
	  <year>
	    <prefix>(</prefix>
	    <suffix>)</suffix>
	  </year>
	</date>

So here I would end up with (YYYY).

I'm still struggling with how to specify rendering for MM-DD or MM, and 
I think I'd like to make the decision based on the XSLT code that would 
actually render the dates.  So, I'd like to go back to this suggestion 
from Mike Kay on how to handle dates that could either be YYYY, 
YYYY-MM, or YYYY-MM-DD.

> If you do want to use the gYearMonth data type, you can write your own
> function f:format-gYearMonth which converts the value to a date:
>
> xs:date(concat($gYM, '-01'))
>
> and then applies format-date() to it.

Basically, what I want to be able to do is to specify a config option 
something like:

<date>
  <month-day/>
</date>

This would apply, for example, to the issue date in a periodical, where 
a complete citation -- with both year at the beginning and month later 
are both drawn from the same mods:dateIssued content -- would look 
like:

	Doe, J. (2000) Some Title, Some Periodical, v2, n3, January, pp. 23-34.

.... or:

	Smith, S. (1999) Some Other Title, Different Periodical, v2, n3, March 
15, pp. 23-34.

So I want the function to do the proper thing whether the date is in 
the form YYYY, YYYY-MM, or YYYY-MM-DD, where in the first case, nothing 
would be rendered, in the second I'd get only the month, and the third 
the month and day.  I also want there to be a parameter that specifies 
either the full month or abbreviated.

The function would then get invoked, I assume, within the template that 
maps the config file to the source data something vaguely like:

<xsl:template match="cs:month-day">
  <xsl:param name="source"/>
  <xsl:apply-templates select="bib:format-month-day{mods:mods)">
    <xsl:with-param name="prefix" select="cs:prefix"/>
    <xsl:with-param name="suffix" select="cs:suffix"/>
  </xsl:apply-templates>
</xsl:template>

The date in this case can be either of these:
 	mods:relatedItem/mods:originInfo/mods:dateIssued
	mods:relatedItem/mods:part/mods:date

I understand conceptually I need to have a choose option in which I am 
testing if the string is castable as xs:gYearMonth or xs:date, and that 
if the former I need to concat the -01 to it but to ignore the day in 
formatting, but I'm not really clear how I put it all together.

Here's where I'm at now:

<xsl:function name="bib:format-month-day" as="xs:integer">
  <xsl:param name="mods" as="element(mods:mods)" />
  <xsl:variable name="date" as="element(mods:dateIssued)"
    select="$mods/mods:originInfo/mods:dateIssued" />
<!-- need above to work for mods:part/mods:date also -->
  <xsl:choose>
    <xsl:when test="$date castable as xs:date">
      ...
    </xsl:when>
    <xsl:when test="$date castable as xs:gYearMonth">
      ...
    </xsl:when>
   <xsl:when test="$date castable as xs:gYear">
      ...
    </xsl:when>
  </xsl:choose>
</xsl:function>

Or is this the wrong approach, and I need to do the testing and 
formatting from within the cs:month-day template, with this function 
only creating the proper date format?

Bruce