Indexing in XSLT

I need some help to solve this problem. Any help is appreciated.

I have an instance document that gives me a list of available dates to
choose from. I get passed another date which I have to compare against this
list and return the matched date.

If no match is found in the list, and the date passed is lower, I need to
return the next higher date from the list. For example, if the date passed
is Aug 10, 2002 and it is not in the available list, I need to return the
next available date which could be Aug 12, 2002. Also I need to check for
month end and year end. So if Aug 30 is passed, I will need to pass back Sep
2 (if available in the list).

The last requirement is if no match is found, and the date passed is higher,
I need to pass a null. For example, the date passed is Sep 30 and the last
date in the list is Aug 15, I need to pass back a null (or empty string).

I have used keys and the sample code I am pasting here is in working mode
and does not include everything I have tried. Any help is appreciated.

Instance XML:
<acquisitions>
	<delivery zip="06850">
		<date>07/31/2002</date>
		<date>08/01/2002</date>
		<date>08/02/2002</date>
		<date>08/05/2002</date>
		<date>08/31/2002</date>
		<date>09/01/2002</date>
	</delivery>
</acquisitions>

XSL (in working draft):

	<xsl:key name="dateindex" match="delivery/date" use="."/>
	<xsl:template match="/">
		<all>
			<xsl:apply-templates
select="acquisitions/delivery"/>
		</all>
	</xsl:template>
	<xsl:template match="delivery">
		<xsl:call-template name="datevar">
			<xsl:with-param name="svcdate"
select="'08/03/2002'"/>
			<xsl:with-param name="deldate"
select="key('dateindex',date[1])"/>
			<xsl:with-param name="totaldates"
select="count(date)"/>
		</xsl:call-template>
	</xsl:template>
	<xsl:template name="datevar">
		<xsl:param name="svcdate"/>
		<xsl:param name="deldate"/>
		<xsl:param name="pos" select="1"/>
		<xsl:param name="totaldates"/>
		<xsl:variable name="delmonth"
select="substring-before($deldate,'/')"/>
		<xsl:variable name="delday"
select="substring-before(substring-after($deldate,'/'),'/')"/>
		<xsl:variable name="delyear"
select="substring-after(substring-after($deldate,'/'),'/')"/>
		<xsl:variable name="svcmonth"
select="substring-before($svcdate,'/')"/>
		<xsl:variable name="svcday"
select="substring-before(substring-after($svcdate,'/'),'/')"/>
		<xsl:variable name="svcyear"
select="substring-after(substring-after($svcdate,'/'),'/')"/>
		<xsl:variable name="daysinmonth">
			<xsl:choose>
				<xsl:when test="$svcmonth='01' or
$svcmonth='03' or $svcmonth='05' or $svcmonth='07' or $svcmonth='08' or
$svcmonth='10' or $svcmonth='12'">
					<xsl:value-of select="31"/>
				</xsl:when>
				<xsl:when test="$svcmonth='04' or
$svcmonth='06' or $svcmonth='09' or $svcmonth='11'">
					<xsl:value-of select="30"/>
				</xsl:when>
				<xsl:when test="$svcmonth='02'">
					<xsl:value-of select="28"/>
				</xsl:when>
			</xsl:choose>
		</xsl:variable>
		<xsl:choose>
			<xsl:when test="$svcday=$delday">
				<xsl:choose>
					<xsl:when
test="$svcmonth=$delmonth">
						<xsl:choose>
							<xsl:when
test="$svcyear=$delyear">
	
<xsl:value-of select="concat($delmonth,'/',$delday,'/',$delyear)"/>
							</xsl:when>
							<xsl:otherwise>
							failed year
							</xsl:otherwise>
						</xsl:choose>
					</xsl:when>
					<xsl:otherwise>
						<xsl:call-template
name="datevar">
							<xsl:with-param
name="svcdate" select="$svcdate"/>
							<xsl:with-param
name="deldate" select="key('dateindex',date[$pos+1])"/>
							<xsl:with-param
name="pos" select="$pos+1"/>
							<xsl:with-param
name="totaldates" select="$totaldates"/>
						</xsl:call-template>
					</xsl:otherwise>
				</xsl:choose>
			</xsl:when>
			<xsl:otherwise>
				<xsl:choose>
					<xsl:when
test="$pos=$totaldates">exhausted list for day match</xsl:when>
					<xsl:otherwise>
						<xsl:call-template
name="datevar">
							<xsl:with-param
name="svcdate" select="$svcdate"/>
							<xsl:with-param
name="deldate" select="key('dateindex',date[$pos+1])"/>
							<xsl:with-param
name="pos" select="$pos+1"/>
							<xsl:with-param
name="totaldates" select="$totaldates"/>
						</xsl:call-template>
					</xsl:otherwise>
				</xsl:choose>
			</xsl:otherwise>
		</xsl:choose>
	</xsl:template>


TIA,

Maulik 

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