XML to CSV (Generation of New Date with input Date) - xslt-2.0

Question

I have a requirement in which I have to generate new date(YYYYMMDD) from the date which is coming in the record(YYYYMMDD) and below is logic for New date creation:
1.If 'MM - 1' = 0, Then make MM -'12', and Year value as YearFromActualDate - 1
2.DD is always '01'
3.If 'MM - 1' != 0, Then MM in output will be 'MM - 1' and Year will remain the same
I have mentioned the Expected Output which will give idea of above mentioned logic.
Please advise.
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:fn="http://www.w3.org/2005/xpath-functions" >
<xsl:output method="text" encoding="utf-8" />
<xsl:param name="delim" select="','" />
<xsl:param name="quote" select="'"'" />
<xsl:param name="break" select="'
'" />
<xsl:template match="/">
<xsl:value-of select="$quote" />
<xsl:text>Name</xsl:text>
<xsl:value-of select="$quote" />
<xsl:value-of select="$delim" />
<xsl:value-of select="$quote" />
<xsl:text>Date</xsl:text>
<xsl:value-of select="$quote" />
<xsl:value-of select="$delim" />
<xsl:value-of select="$quote" />
<xsl:text>NewDate</xsl:text>
<xsl:value-of select="$quote" />
<xsl:value-of select="$break" />
<xsl:apply-templates select="ID/ED/E1" />
</xsl:template>
<xsl:template match="E1">
<xsl:value-of select="$quote" />
<xsl:value-of select="name"/>
<xsl:value-of select="$quote" />
<xsl:value-of select="$delim" />
<xsl:value-of select="$quote" />
<xsl:value-of select="date"/>
<xsl:value-of select="$quote" />
<xsl:value-of select="$delim" />
<xsl:value-of select="$quote" />
<xsl:variable name="newdate" select="'01'" />
<xsl:variable name="inMonth" select="substring(date,5,2)" />
<xsl:variable name="inputYear" select="substring(date,1,4)" />
<xsl:choose>
<xsl:when test = "$inMonth='01'">
<xsl:variable name="calculatedMonth" select="12"/>
<xsl:value-of select="concat(xs:integer($inputYear) - 1,$calculatedMonth,$newdate)" />
</xsl:when>
<xsl:otherwise>
<xsl:variable name="inMonthlength" select="string-length(xs:string(xs:integer($inMonth) - 1))" />
<xsl:if test="xs:integer($inMonthlength) !=2">
<xsl:value-of select="concat($inputYear,concat(0,xs:integer($inMonth) - 1),$newdate)" />
</xsl:if>
<xsl:if test="xs:integer($inMonthlength) =2">
<xsl:value-of select="concat($inputYear,(xs:integer($inMonth) - 1),$newdate)" />
</xsl:if>
</xsl:otherwise>
</xsl:choose>
<xsl:value-of select="$quote"/>
<xsl:if test="following-sibling::*">
<xsl:value-of select="$break" />
</xsl:if>
</xsl:template>
Input:
<ID>
<ED>
<E1>
<name>Eva</name>
<date>20190504</date> (Consider date as YYYYMMDD)
</E1>
<E1>
<name>Alan</name>
<date>20190101</date>
</E1>
</ED>
<ID>
Expected Output:
"Name","Date","NewDate"
"Eva","20190504","20190401"
"Alan","20190101","20181201"

Answer 1

If I've reverse-engineered your algorithm correctly, what you want is the first day of the previous month.
Logically the steps are:
Convert your date to an xs:date value
Take the first day of the current month
Subtract one month.
In practice it's simplest to combine (1) and (2) so you end up with
xs:date(replace($date, '(....)(..)(..)', '$1-$2-01')) - xs:yearMonthDuration('P1M')
and then you can format this date as YYYYMMDD using
format-date($date, '[Y0001][M01][D01]')