XSLT 2.0: Evaluate and modify element value according to current index of for-each -group

Question

I am trying to evaluate EndDate as next "StartDate -1" (a day before next start date). Given below is the input XML:

<?xml version="1.0" encoding="UTF-8"?>
<queryCompoundEmployeeResponse>
   <CompoundEmployee>
         <id>176</id>
         <person>
               <action>NO CHANGE</action>
               <person_id_external>10005005</person_id_external>
               <personal_information>
                     <end_date>9999-12-31</end_date>
                     <start_date>2021-06-03</start_date>
               </personal_information>
               <personal_information>
                     <end_date>2021-06-02</end_date>
                     <start_date>2017-12-06</start_date>
               </personal_information>
               <phone_information>
                     <phone_type>B</phone_type>
               </phone_information>
               <phone_information>
                     <phone_number>7CAED430A494B3C404</phone_number>
               </phone_information>
               <email_information>
                     <last_modified_on>2019-03-25T02:44:51.000Z</last_modified_on>
               </email_information>
               <employment_information>
                     <start_date>2017-12-06</start_date>
                     <user_id>10005005</user_id>
                     <job_information>
                           <end_date>9999-12-31</end_date>
                           <start_date>2019-03-02</start_date>
                        </job_information>
               </employment_information>
         </person>
         <execution_timestamp>2021-07-14T15:08:38.000Z</execution_timestamp>
         <version_id>2105P0</version_id>
      <Start_Dates>
         <StartDate>2017-12-06</StartDate>
         <StartDate>2017-12-06</StartDate>
         <StartDate>2019-03-02</StartDate>
         <StartDate>2021-06-03</StartDate>
      </Start_Dates>
      <End_Dates>
         <EndDate>2021-06-02</EndDate>
         <EndDate>NA</EndDate>
         <EndDate>9999-12-31</EndDate>
         <EndDate>9999-12-31</EndDate>
      </End_Dates>
   </CompoundEmployee>
   </queryCompoundEmployeeResponse>

Current Output:

    <?xml version="1.0" encoding="UTF-8"?>
<queryCompoundEmployeeResponse xmlns:xs="http://www.w3.org/2001/XMLSchema">
   <CompoundEmployee>
      <Person>
         <StartDate>2017-12-06</StartDate>
         <EndDate>2019-03-01</EndDate>
      </Person>
      <Person>
         <StartDate>2019-03-02</StartDate>
         <EndDate/>
      </Person>
      <Person>
         <StartDate>2021-06-03</StartDate>
         <EndDate>9999-12-31</EndDate>
      </Person>
   </CompoundEmployee>
</queryCompoundEmployeeResponse>

Required Output:

<?xml version="1.0" encoding="UTF-8"?>
<queryCompoundEmployeeResponse xmlns:xs="http://www.w3.org/2001/XMLSchema">
   <CompoundEmployee>
      <Person>
         <StartDate>2017-12-06</StartDate>
         <EndDate>2019-03-01</EndDate>
      </Person>
      <Person>
         <StartDate>2019-03-02</StartDate>
         <EndDate>2021-06-02</EndDate>
      </Person>
      <Person>
         <StartDate>2021-06-03</StartDate>
         <EndDate>9999-12-31</EndDate>
      </Person>
   </CompoundEmployee>
</queryCompoundEmployeeResponse>

I am trying to calculate the EndDate as a day minus next StartDate for each Person node. For last Person, the EndDate should be the last EndDate in the input XML.

Here is the code that I am trying to enhance:

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/queryCompoundEmployeeResponse">
    <queryCompoundEmployeeResponse>
        <xsl:for-each select="CompoundEmployee">
            <xsl:copy>
                <xsl:variable name="person" select="person" />
                <xsl:for-each-group select="Start_Dates/StartDate" group-by=".">
                    <Person>
                       <xsl:copy-of select="."/>
                       
                        <!--Start of EndDate logic for last record-->
                        <xsl:variable name="nxtStartDate" select="following-sibling::StartDate"/>
                           <xsl:if test="not($nxtStartDate)">
                             <xsl:variable name="i" select="position()"/>
                                <EndDate>
                                    <xsl:value-of select="../following-sibling::End_Dates/EndDate[last()]"/>   
                                </EndDate>
                           </xsl:if>
                          <!-- End of EndDate logic for last record-->  
                          
                          <!--Calculate next start date -1 -->
                            <xsl:if test="$nxtStartDate">
                            <xsl:variable name="currentDate" select="Start_Dates/StartDate"/>
                            <xsl:variable name="i" select="position()"/>
                            <EndDate>
                                <xsl:apply-templates select="following-sibling::StartDate[$i+1]"/>
                            </EndDate>
                            </xsl:if>
                      <!--Calculate next start date -1 -->
                    
                     <!-- //Some additional required code://
                     
                       <xsl:copy-of select="$person/* except $person/(personal_information | phone_information | email_information | employment_information)"/>
                       <xsl:copy-of select="$person/personal_information[start_date le current() and current() le end_date]"/>
                       <xsl:copy-of select="$person/employment_information[start_date le current() and current() le end_date]"/>
                        <xsl:copy-of select="$person/employment_information/job_information[start_date le current() and current() le end_date]"/> 
                     -->
                    </Person>
                </xsl:for-each-group>
            </xsl:copy>
        </xsl:for-each>
    </queryCompoundEmployeeResponse>
</xsl:template>

<xsl:template match="StartDate">
 <xsl:variable name="sDate" select="." as="xs:date"/>
        <xsl:copy-of select="$sDate - 1*xs:dayTimeDuration('P1D')"/>
</xsl:template>
    
</xsl:stylesheet>



 I need something like following-sibling::(.)[index+1]. It gives me the End date in first Person. But next one is still empty. 

What am I doing wrong? Also, how can I modify this to have separate templates for each part?

Thanks in advance!

Answer 1

When you do xsl:for-each-group, you are placed in the context of the first item in the group. From this context, your expression following-sibling::StartDate selects the following siblings of the group's first StartDate in the original XML document - not in the current group. And you certainly can't use any of the axes to get to the first item of the next group - which is what you really want.

Try it perhaps this way:

XSLT 2.0

<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="xs">
<xsl:output method="xml" version="1.0" encoding="utf-8" indent="yes"/>

<xsl:template match="/queryCompoundEmployeeResponse">
    <queryCompoundEmployeeResponse>
        <xsl:for-each select="CompoundEmployee">
            <xsl:copy>
            
                <xsl:variable name="start-dates">
                    <xsl:for-each-group select="Start_Dates/StartDate" group-by=".">
                        <xsl:copy-of select="."/>
                    </xsl:for-each-group>
                </xsl:variable>
            
                <xsl:for-each select="$start-dates/StartDate">
                    <Person>
                        <xsl:copy-of select="."/>
                        <xsl:variable name="next" select="following-sibling::StartDate[1]"/>   
                        <EndDate>
                            <xsl:value-of select="if ($next) then xs:date($next) - xs:dayTimeDuration('P1D') else '9999-12-31'"/>   
                         </EndDate>
                    </Person>
                </xsl:for-each>
                
            </xsl:copy>
        </xsl:for-each>
    </queryCompoundEmployeeResponse>
</xsl:template>

</xsl:stylesheet>

---

Note: this is a quick draft; it can probably be streamlined a bit - maybe along the lines of:

<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="xs">
<xsl:output method="xml" version="1.0" encoding="utf-8" indent="yes"/>

<xsl:template match="/queryCompoundEmployeeResponse">
    <queryCompoundEmployeeResponse>
        <xsl:for-each select="CompoundEmployee">
            <xsl:copy>
                <xsl:variable name="start-dates" select="distinct-values(Start_Dates/StartDate)"/>
                <xsl:for-each select="$start-dates">
                    <Person>
                        <StartDate>
                            <xsl:value-of select="."/>   
                        </StartDate>
                        <xsl:variable name="i" select="position()"/>   
                        <EndDate>                       
                            <xsl:value-of select="if ($i != last()) then xs:date($start-dates[$i+ 1]) - xs:dayTimeDuration('P1D') else '9999-12-31'"/>
                        </EndDate>
                    </Person>
                </xsl:for-each>
            </xsl:copy>
        </xsl:for-each>
    </queryCompoundEmployeeResponse>
</xsl:template>

</xsl:stylesheet>