Overwriting nodes within a node tree in xslt - xslt

Question

This is my input
<SimpleInput>
<variable1>1</variable1>
<variable2>2</variable2>
<variable3>3</variable3>
</SimpleInput>
This is the output i am geting now
<Classes>
<ClassA>
<input1>overwrite 1</input1>
<input2>2</input2>
<input3>3</input3>
</ClassA>
<ClassB>
<input1>1</input1>
<input2>overwrite 2</input2>
<input3>3</input3>
</ClassB>
</Classes>
This is how i have achieved the above
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="UTF-8" indent="yes" />
<xsl:variable name="myVar">
<input1><xsl:value-of select="/SimpleInput/variable1"/></input1>
<input2><xsl:value-of select="/SimpleInput/variable2"/></input2>
<input3><xsl:value-of select="/SimpleInput/variable3"/></input3>
</xsl:variable>
<xsl:template match="/">
<Classes>
<xsl:variable name="paramForClassA">
<input1><xsl:value-of select="'overwrite 1'"/></input1>
<input2><xsl:value-of select="/SimpleInput/variable2"/></input2>
<input3><xsl:value-of select="/SimpleInput/variable3"/></input3>
</xsl:variable>
<ClassA>
<xsl:call-template name="buildSection">
<xsl:with-param name="obj" select="$paramForClassA"/>
</xsl:call-template>
</ClassA>
<ClassB>
<xsl:variable name="paramForClassB">
<input1><xsl:value-of select="/SimpleInput/variable1"/></input1>
<input2><xsl:value-of select="'overwrite 2'"/></input2>
<input3><xsl:value-of select="/SimpleInput/variable3"/></input3>
</xsl:variable>
<xsl:call-template name="buildSection">
<xsl:with-param name="obj" select="$paramForClassB"/>
</xsl:call-template>
</ClassB>
</Classes>
</xsl:template>
<xsl:template name="buildSection">
<xsl:param name="obj" select="()"/>
<xsl:for-each select="$obj/*">
<xsl:element name="{name()}">
<xsl:copy-of select="#*|node()" />
</xsl:element>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
But I want to be able to overwrite/create the nodes i want dynamically without rebuilding the entire node tree before passing it to the buildSection template.
Below is an example of the output I am looking for (with an additional input4 on ClassB which i am not able to achieve with the code above)
<Classes>
<ClassA>
<input1>overwrite 1</input1>
<input2>2</input2>
<input3>3</input3>
</ClassA>
<ClassB>
<input1>1</input1>
<input2>overwrite 2</input2>
<input3>3</input3>
<input4>New Item</input4>
</ClassB>
</Classes>
Something similar to what is done here, but i am looking to replace or add the node itself if it doesnt exist.
There are 2 limitations with my current design which i am looking to overcome when passing the parameter to a template call.
Adding new elements to ClassX if necessary
Removing the need to rebuild the entire node tree (There could be over 80 variable in the node tree in some cases)
The build template is actually in a separate file and could be used from multiple callers. If we hard code the node tree building logic in each class (which are also in separate files), if there is a requirement to update the template, then I will need to also update all the callers (which can be upto 30 separate ones). Hope this explains the necessity of the new design.
Ideally something like this when building paramForX
<xsl:variable name="myReplacementsForA">
<input1>overwrite 1</input1>
</xsl:variable>
<xsl:variable name="myReplacementsForB">
<input2>overwrite 2</input2>
<input4>Add 4</input4>
</xsl:variable>
<xsl:variable name="paramForClassA">
<xsl:apply-templates select="$myVar" mode="add-or-replace-value">
<with-param name="replacements" select="$myReplacementsForA"/>
</xsl:apply-templates>
</xsl:variable>
<xsl:variable name="paramForClassB">
<xsl:apply-templates select="$myVar" mode="add-or-replace-value">
<with-param name="replacements" select="$myReplacementsForB"/>
</xsl:apply-templates>
</xsl:variable>

Answer 1

I managed to do it this way. Not sure if it is the most efficient
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="UTF-8" indent="yes" />
<xsl:variable name="myVar">
<input1><xsl:value-of select="/SimpleInput/variable1"/></input1>
<input2><xsl:value-of select="/SimpleInput/variable2"/></input2>
<input3><xsl:value-of select="/SimpleInput/variable3"/></input3>
</xsl:variable>
<xsl:template match="/">
<Classes>
<xsl:variable name="myReplacementsForA">
<input1>overwrite 1</input1>
</xsl:variable>
<xsl:variable name="paramForClassA">
<xsl:apply-templates mode="buildNewParam">
<xsl:with-param name="original" select="$myVar"/>
<xsl:with-param name="replacements" select="$myReplacementsForA"/>
</xsl:apply-templates>
</xsl:variable>
<ClassA>
<xsl:value-of select="$paramForClassA/item2"/>
<xsl:call-template name="buildSection">
<xsl:with-param name="obj" select="$paramForClassA"/>
</xsl:call-template>
</ClassA>
<ClassB>
<xsl:variable name="myReplacementsForB">
<input2>overwrite 2</input2>
<input4>Add 4</input4>
</xsl:variable>
<xsl:variable name="paramForClassB">
<xsl:apply-templates mode="buildNewParam">
<xsl:with-param name="original" select="$myVar"/>
<xsl:with-param name="replacements" select="$myReplacementsForB"/>
</xsl:apply-templates>
</xsl:variable>
<xsl:call-template name="buildSection">
<xsl:with-param name="obj" select="$paramForClassB"/>
</xsl:call-template>
</ClassB>
</Classes>
</xsl:template>
<xsl:template name="buildSection">
<xsl:param name="obj" select="()"/>
<xsl:for-each select="$obj/*">
<xsl:element name="{name()}">
<xsl:copy-of select="#*|node()" />
</xsl:element>
</xsl:for-each>
</xsl:template>
<xsl:template mode="buildNewParam" match=".">
<xsl:param name="original"/>
<xsl:param name="replacements"/>
<xsl:variable name="merged">
<xsl:for-each select="$original/*">
<xsl:element name="{name()}">
<xsl:copy-of select="#*|node()" />
</xsl:element>
</xsl:for-each>
<xsl:for-each select="$replacements/*">
<xsl:element name="{name()}">
<xsl:copy-of select="#*|node()" />
</xsl:element>
</xsl:for-each>
</xsl:variable>
<xsl:variable name="sorted">
<xsl:for-each select="$merged/*">
<xsl:sort select="name()"/>
<xsl:element name="{name()}">
<xsl:copy-of select="#*|node()" />
</xsl:element>
</xsl:for-each>
</xsl:variable>
<xsl:for-each select="$sorted/*">
<xsl:if test="name()!=name(following-sibling::node()[1])">
<xsl:element name="{name()}">
<xsl:copy-of select="#*|node()" />
</xsl:element>
</xsl:if>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>