Replacing the namespace in input xml - xslt

Question

I have two types of input xml, one with namespace prefix and another one without prefix and i want to replace the namespaces.
Sample1
<v1:Library xmlns:v1="http://testlibrary" xmlns:v2="http://commonprice">
<v1:Books_details>
<v1:Name>test1</v1:Name>
<v1:title>test2</v1:title>
<v2:price xmlns="http://commonprice">12</v2:price>
</v1:Books_details>
</v1:Library>
Sample2
<Library xmlns="http://testlibrary">
<Books_details>
<Name>test1</Name>
<title>test2</title>
<price xmlns="http://commonprice">12</price>
</Books_details>
</Library>
I have written following XSLT to change the namespace from "http://testlibrary" to "http://newlibrary" and it works fine for sample1 but it doesn't work for the sample2. It gives wrong result. It also the change the namespace of the price element even though it doesn't have namespace to be replaced.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xsl:param name="old_namespace"/>
<xsl:param name="new_namespace"/>
<xsl:template match="/">
<xsl:apply-templates select="#* | node()"/>
</xsl:template>
<xsl:template match="text() | comment() | processing-instruction()">
<xsl:copy>
<xsl:apply-templates select="text() | comment() | processing-instruction()"/>
</xsl:copy>
</xsl:template>
<!-- Template used to copy elements -->
<xsl:template match="*">
<xsl:variable name="name">
<xsl:choose>
<xsl:when test="contains(name(), ':')">
<xsl:value-of select="name()"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="local-name()"/>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>
<xsl:element name="{$name}" namespace="{$new_namespace}">
<!-- Copy all namespace through except for namespace to be changed -->
<xsl:for-each select="namespace::*">
<xsl:if test="string(.)!=$old_namespace">
<xsl:copy-of select="."/>
</xsl:if>
</xsl:for-each>
<xsl:apply-templates select="node()|#*"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>

Answer 1

Note: My first answer was wrong because in XSLT 1.0, you can't use variable references within a match pattern.
This style-sheet will take either Sample1 or Sample2 as input document and replace all occurrences of the old namespace, from the element names, with the new namespace. Note: you can change the xsl:variable for xsl:param.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:variable name="old_namespace" select="'http://testlibrary'" />
<xsl:variable name="new_namespace" select="'http://newlibrary'" />
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="*">
<xsl:choose>
<xsl:when test="namespace-uri()=$old_namespace">
<xsl:element name="{local-name()}" namespace="{$new_namespace}">
<xsl:apply-templates select="#*|node()"/>
</xsl:element>
</xsl:when>
<xsl:otherwise>
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>
Caveat
The above style-sheet will only change the namespace of the elements. It will not change the namespaces of attributes, nor will it remove extraneous namespaces nodes.
On a more specific solution
It is very unusual to require a general solution for an operation on a variable namespace. Namespaces, being what they are tend to be fixed and known. Consider carefully, if you really need a generalized solution. If you need a specific solution, meaning replacing occurrences of a specific namespace, then things get a lot easier, such as with this style-sheet...
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:old="http://testlibrary"
xmlns:new="http://newlibrary">
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="old:*">
<xsl:element name="{local-name()}" namespace="http://newlibrary">
<xsl:apply-templates select="#*|node()" />
</xsl:element>
</xsl:template>
</xsl:stylesheet>
UPDATE
I just noticed Dimitre's solution to a very similar question here.