From 0707ada63bf5662c34b8f8fab60291840377217c Mon Sep 17 00:00:00 2001
From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Fri, 14 Sep 2018 12:48:10 +0200
Subject: XSLT stylesheet to convert cmark XML back to Commonmark

Initial version of an XSLT stylesheet that converts the XML format
produced by `cmark -t xml` back to Commonmark.

Fixes #264
---
 tools/xml2md.xsl | 308 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 308 insertions(+)
 create mode 100644 tools/xml2md.xsl

diff --git a/tools/xml2md.xsl b/tools/xml2md.xsl
new file mode 100644
index 0000000..2fc7ce1
--- /dev/null
+++ b/tools/xml2md.xsl
@@ -0,0 +1,308 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!--
+
+xml2md.xsl
+==========
+
+This XSLT stylesheet transforms the cmark XML format back to Commonmark.
+Since the XML output is lossy, a lossless MD->XML->MD roundtrip isn't
+possible. The XML->MD->XML roundtrip should produce the original XML,
+though.
+
+HTML blocks and inlines aren't supported.
+
+Example usage with xsltproc:
+
+    cmark -t xml doc.md | xsltproc -novalid xml2md.xsl -
+
+-->
+
+<xsl:stylesheet
+    version="1.0"
+    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+    xmlns:md="http://commonmark.org/xml/1.0">
+
+<xsl:output method="text" encoding="utf-8"/>
+
+<!-- Generic templates -->
+
+<xsl:template match="/ | md:document | md:list">
+    <xsl:apply-templates select="md:*"/>
+</xsl:template>
+
+<xsl:template match="md:*">
+    <xsl:message>Unsupported element '<xsl:value-of select="local-name()"/>'</xsl:message>
+</xsl:template>
+
+<xsl:template match="md:*" mode="indent"/>
+
+<!-- Indent blocks -->
+
+<xsl:template match="md:*" mode="indent-block">
+    <xsl:if test="preceding-sibling::md:*">
+        <xsl:if test="not(ancestor::md:list[1][@tight='true'])">
+            <xsl:apply-templates select="ancestor::md:*" mode="indent"/>
+            <xsl:text>&#10;</xsl:text>
+        </xsl:if>
+        <xsl:apply-templates select="ancestor::md:*" mode="indent"/>
+    </xsl:if>
+</xsl:template>
+
+<!-- Heading -->
+
+<xsl:template match="md:heading">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <xsl:value-of select="substring('###### ', 7 - @level)"/>
+    <xsl:apply-templates select="md:*"/>
+    <xsl:text>&#10;</xsl:text>
+</xsl:template>
+
+<!-- Paragraph -->
+
+<xsl:template match="md:paragraph">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <xsl:apply-templates select="md:*"/>
+    <xsl:text>&#10;</xsl:text>
+</xsl:template>
+
+<!-- Thematic break -->
+
+<xsl:template match="md:thematic_break">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <xsl:text>***&#10;</xsl:text>
+</xsl:template>
+
+<!-- List -->
+
+<xsl:template match="md:list">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <xsl:apply-templates select="md:*"/>
+</xsl:template>
+
+<xsl:template match="md:item">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <xsl:choose>
+        <xsl:when test="../@type = 'bullet'">-</xsl:when>
+        <xsl:when test="../@type = 'ordered'">
+            <xsl:value-of select="../@start + position() - 1"/>
+            <xsl:choose>
+                <xsl:when test="../@delim = 'period'">.</xsl:when>
+                <xsl:when test="../@delim = 'paren'">)</xsl:when>
+            </xsl:choose>
+        </xsl:when>
+    </xsl:choose>
+    <xsl:text> </xsl:text>
+    <xsl:apply-templates select="md:*"/>
+</xsl:template>
+
+<xsl:template match="md:item" mode="indent">
+    <xsl:choose>
+        <xsl:when test="../@type = 'bullet'">
+            <xsl:text>  </xsl:text>
+        </xsl:when>
+        <xsl:when test="../@type = 'ordered'">
+            <xsl:text>   </xsl:text>
+        </xsl:when>
+    </xsl:choose>
+</xsl:template>
+
+<!-- Block quote -->
+
+<xsl:template match="md:block_quote">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <xsl:text>&gt; </xsl:text>
+    <xsl:apply-templates select="md:*"/>
+</xsl:template>
+
+<xsl:template match="md:block_quote" mode="indent">
+    <xsl:text>&gt; </xsl:text>
+</xsl:template>
+
+<!-- Code block -->
+
+<xsl:template match="md:code_block">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <!-- TODO: Longer delimiter if text contains ``` -->
+    <xsl:text>```</xsl:text>
+    <xsl:value-of select="@info"/>
+    <xsl:text>&#10;</xsl:text>
+    <xsl:call-template name="indent-lines">
+        <xsl:with-param name="code" select="."/>
+    </xsl:call-template>
+    <xsl:apply-templates select="ancestor::md:*" mode="indent"/>
+    <xsl:text>```</xsl:text>
+    <xsl:text>&#10;</xsl:text>
+</xsl:template>
+
+<!-- Inline HTML -->
+
+<xsl:template match="md:html_block">
+    <xsl:apply-templates select="." mode="indent-block"/>
+    <xsl:value-of select="substring-before(., '&#10;')"/>
+    <xsl:text>&#10;</xsl:text>
+    <xsl:call-template name="indent-lines">
+        <xsl:with-param name="code" select="substring-after(., '&#10;')"/>
+    </xsl:call-template>
+</xsl:template>
+
+<!-- Indent multiple lines -->
+
+<xsl:template name="indent-lines">
+    <xsl:param name="code"/>
+    <xsl:if test="contains($code, '&#10;')">
+        <xsl:apply-templates select="ancestor::md:*" mode="indent"/>
+        <xsl:value-of select="substring-before($code, '&#10;')"/>
+        <xsl:text>&#10;</xsl:text>
+        <xsl:call-template name="indent-lines">
+            <xsl:with-param name="code" select="substring-after($code, '&#10;')"/>
+        </xsl:call-template>
+    </xsl:if>
+</xsl:template>
+
+<!-- Text -->
+
+<xsl:template match="md:text">
+    <xsl:variable name="t" select="string(.)"/>
+    <xsl:variable name="first" select="substring($t, 1, 1)"/>
+    <xsl:variable name="marker-check" select="translate(substring($t, 1, 10), '0123456789', '')"/>
+    <xsl:choose>
+        <!-- Escape ordered list markers -->
+        <xsl:when test="starts-with($marker-check, '.') and $first != '.'">
+            <xsl:value-of select="substring-before($t, '.')"/>
+            <xsl:text>\.</xsl:text>
+            <xsl:call-template name="escape-text">
+                <xsl:with-param name="text" select="substring-after($t, '.')"/>
+            </xsl:call-template>
+        </xsl:when>
+        <xsl:when test="starts-with($marker-check, ')') and $first != ')'">
+            <xsl:value-of select="substring-before($t, ')')"/>
+            <xsl:text>\)</xsl:text>
+            <xsl:call-template name="escape-text">
+                <xsl:with-param name="text" select="substring-after($t, ')')"/>
+            </xsl:call-template>
+        </xsl:when>
+        <!-- Escape leading block characters -->
+        <xsl:when test="contains('-+>#=~', $first)">
+            <xsl:text>\</xsl:text>
+            <xsl:value-of select="$first"/>
+            <xsl:call-template name="escape-text">
+                <xsl:with-param name="text" select="substring($t, 2)"/>
+            </xsl:call-template>
+        </xsl:when>
+        <!-- Otherwise -->
+        <xsl:otherwise>
+            <xsl:call-template name="escape-text">
+                <xsl:with-param name="text" select="$t"/>
+            </xsl:call-template>
+        </xsl:otherwise>
+    </xsl:choose>
+</xsl:template>
+
+<!-- Breaks -->
+
+<xsl:template match="md:softbreak">
+    <xsl:text>&#10;</xsl:text>
+    <xsl:apply-templates select="ancestor::md:*" mode="indent"/>
+</xsl:template>
+
+<xsl:template match="md:linebreak">
+    <xsl:text>  &#10;</xsl:text>
+    <xsl:apply-templates select="ancestor::md:*" mode="indent"/>
+</xsl:template>
+
+<!-- Emphasis -->
+
+<xsl:template match="md:emph">
+    <xsl:text>*</xsl:text>
+    <xsl:apply-templates select="md:*"/>
+    <xsl:text>*</xsl:text>
+</xsl:template>
+
+<xsl:template match="md:strong">
+    <xsl:text>**</xsl:text>
+    <xsl:apply-templates select="md:*"/>
+    <xsl:text>**</xsl:text>
+</xsl:template>
+
+<!-- Inline code -->
+
+<xsl:template match="md:code">
+    <xsl:call-template name="escape-code">
+        <xsl:with-param name="text" select="string(.)"/>
+    </xsl:call-template>
+</xsl:template>
+
+<xsl:template name="escape-code">
+    <xsl:param name="text"/>
+    <xsl:param name="delim" select="'`'"/>
+
+    <xsl:choose>
+        <xsl:when test="contains($text, $delim)">
+            <xsl:call-template name="escape-code">
+                <xsl:with-param name="text" select="$text"/>
+                <xsl:with-param name="delim" select="concat($delim, '`')"/>
+            </xsl:call-template>
+        </xsl:when>
+        <xsl:otherwise>
+            <xsl:value-of select="$delim"/>
+            <xsl:value-of select="$text"/>
+            <xsl:value-of select="$delim"/>
+        </xsl:otherwise>
+    </xsl:choose>
+</xsl:template>
+
+<!-- Links and images -->
+
+<xsl:template match="md:link | md:image">
+    <xsl:if test="self::md:image">!</xsl:if>
+    <xsl:text>[</xsl:text>
+    <xsl:apply-templates select="md:*"/>
+    <xsl:text>](</xsl:text>
+    <xsl:call-template name="escape-text">
+        <xsl:with-param name="text" select="string(@destination)"/>
+        <xsl:with-param name="escape" select="'()'"/>
+    </xsl:call-template>
+    <xsl:if test="string(@title)">
+        <xsl:text> "</xsl:text>
+        <xsl:call-template name="escape-text">
+            <xsl:with-param name="text" select="string(@title)"/>
+            <xsl:with-param name="escape" select="'&quot;'"/>
+        </xsl:call-template>
+        <xsl:text>"</xsl:text>
+    </xsl:if>
+    <xsl:text>)</xsl:text>
+</xsl:template>
+
+<!-- Inline HTML -->
+
+<xsl:template match="md:html_inline">
+    <xsl:value-of select="."/>
+</xsl:template>
+
+<!-- Escape text -->
+
+<xsl:template name="escape-text">
+    <xsl:param name="text"/>
+    <xsl:param name="escape" select="'*_`&lt;[]&amp;'"/>
+
+    <xsl:variable name="trans" select="translate($text, $escape, '\\\\\\\')"/>
+    <xsl:choose>
+        <xsl:when test="contains($trans, '\')">
+            <xsl:variable name="safe" select="substring-before($trans, '\')"/>
+            <xsl:variable name="l" select="string-length($safe)"/>
+            <xsl:value-of select="$safe"/>
+            <xsl:text>\</xsl:text>
+            <xsl:value-of select="substring($text, $l + 1, 1)"/>
+            <xsl:call-template name="escape-text">
+                <xsl:with-param name="text" select="substring($text, $l + 2)"/>
+                <xsl:with-param name="escape" select="$escape"/>
+            </xsl:call-template>
+        </xsl:when>
+        <xsl:otherwise>
+            <xsl:value-of select="$text"/>
+        </xsl:otherwise>
+    </xsl:choose>
+</xsl:template>
+
+</xsl:stylesheet>
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