Concat two xml values with XSLT

The use-case described in this blog-post,is there's an WSO2 ESB node setup to proxy an incoming message to a particular back-end endpoint. 
Before delivering the message to the back-end endpoint,from the ESB node itself,this incoming message need to processed and change its inside xml payload format.

For eg: Below is the incoming message

<?xml version="1.0" encoding="UTF-8"?>

<CinemaHall name="liberty">

<OwnerData>

<Name>John Smith</Name>

<openedDate>12/12/80</openedDate>

<quality>good</quality>

</OwnerData>

<CinemaHallData>

<rows>100</rows>

<seats>

<seat>50</seat>

<seat>60</seat>

</seats>

</CinemaHallData>

</CinemaHall>

This message need to be changed as  below;

<?xml version="1.0" encoding="UTF-8"?>

<CinemaHall name="liberty">

<OwnerData>

<Name>John Smith</Name>

<openedDate>12/12/80</openedDate>

<quality>good</quality>

</OwnerData>

<CinemaHallData>

<rows>100</rows>

<seats> 50,60 </seats>

</CinemaHallData>

</CinemaHall>

Note I have highlighted which part of the payload need to be changed. So how to do that change. Simply you can use XSLT[XSL Transformations] support here.XSL means XSL stands for EXtensible Stylesheet Language, and is a style sheet language for XML documents.Simply to do a XSLT transformation from ESB,you can use the support of in-built XSLT mediator in it. Additionally you will a XSL stylesheet which contains the conversion source logic apart from incoming XML payload.

In the above example conversion,you'll see there are multiple XML elements called <seat> in the XML input payload and thus,you need to iterate through each <seat> element and get each value of it and concat those values with a ',' at each iteration.And specially appending of ',' need to avoid in last iterated <seat>  value.

Thus xsl sheet would contain,a for loop and if-else condition as the conversion source.

In XSLT world for loop => < xsl:for-each> &lt/xsl:for-each>   and if-else condition =>< xsl:choose>  < xsl:when> < /xsl:when> <xsl:choose> 

And the sample xsl sheet source for above conversion is as below;

<?xml version="1.0" encoding="ISO-8859-1"?>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

  <xsl:template match="node()|@*">

        <xsl:copy>

            <xsl:apply-templates select="node()|@*"/>

        </xsl:copy>

    </xsl:template>

    <xsl:template match="//CinemaHall/CinemaHallData/seats">

    <seats>

   <xsl:for-each select="//CinemaHall/CinemaHallData/seats/seat">

        <xsl:variable name="i" select="position()" />  

     <xsl:choose>

     <xsl:when test="count(//CinemaHall/CinemaHallData/seats/seat)-position() >=1">      

         <xsl:value-of select="concat(//CinemaHall/CinemaHallData/seats/seat[$i] , ',')"/>

      </xsl:when>

      <xsl:when test="count(//CinemaHall/CinemaHallData/seats/seat)-position() =0">      

        <xsl:value-of select="//CinemaHall/CinemaHallData/seats/seat[$i]"/>

      </xsl:when>

   </xsl:choose>

    </xsl:for-each> 

   </seats> 

    </xsl:template>

</xsl:stylesheet>

Note to test,my XSL sheet correctness,I used online provided XSLT tool support.