Use dcfilename if base is empty

* Derive output filename from base and dcfilename
* Introduce new parameter json-ld.ext (".json") that holds the
  filename extension

suse2022-ns/xhtml/json-ld.xsl

@@ -155,9 +155,8 @@
           <xsl:when test="$node/@xml:base">
             <xsl:value-of select="substring-before($node/@xml:base, '.xml')" />
           </xsl:when>
-          <xsl:when
-            test="($node/@id or $node/@xml:id) and $use.id.as.filename != 0">
-            <xsl:value-of select="($node/@id | $node/@xml:id)[1]" />
+          <xsl:when test="$node/@xml:id and $use.id.as.filename != 0">
+            <xsl:value-of select="$node/@xml:id" />
           </xsl:when>
           <xsl:otherwise /><!-- TODO: What do we do here, if nothing works? -->
         </xsl:choose>
@@ -190,8 +189,20 @@
         <xsl:with-param name="node" select="$node"/>
       </xsl:call-template>
     </xsl:variable>
-    <xsl:variable name="filename" select="concat($base, '.json')"/>
-    <xsl:variable name="dcfile" select="concat('DC-', $base)"/>
+    <xsl:variable name="filename">
+      <xsl:variable name="dcfile">
+        <xsl:call-template name="get-dc-filename"/>
+      </xsl:variable>
+      <xsl:variable name="file" select="substring-after($dcfile, 'DC-')"/>
+      <xsl:choose>
+        <xsl:when test="$base != ''">
+          <xsl:value-of select="concat($base, $json-ld.ext)"/>
+        </xsl:when>
+        <xsl:otherwise>
+          <xsl:value-of select="concat($file, $json-ld.ext)"/>
+        </xsl:otherwise>
+      </xsl:choose>
+    </xsl:variable>
     <xsl:variable name="content">
       <xsl:call-template name="generate-json-content">
         <xsl:with-param name="node" select="$node"/>

suse2022-ns/xhtml/param.xsl

@@ -469,6 +469,8 @@ task before
   <xsl:param name="stitchfile"/>
   <!-- Should the individual authors be used? 0=no, 1=yes  -->
   <xsl:param name="json-ld-use-individual-authors" select="1"/>
+  <!-- File extension -->
+  <xsl:param name="json-ld.ext">.json</xsl:param>
   <!-- Timezone -->
   <xsl:param name="json-ld-date-timezone">+02:00</xsl:param>
   <xsl:param name="json-ld-fallback-author-name">SUSE Product &amp; Solution Documentation Team</xsl:param>