#/usr/bin/ruby
require 'html5'

unless ARGV.first =~ /.tmpl$/ and ARGV.length == 1
  STDERR.puts "Usage: ruby #{__FILE__} index.html.tmpl"
  exit 86
end

tmpl = open(ARGV.first) {|file| file.read}

# convert variable names to xpath expressions
xpath = proc do |name|
  case name
  when 'Channels'       then 'planet:source'
  when 'Items'          then 'atom:entry'

  when 'channel_link'   then "atom:source/atom:link[@rel='alternate']/@href"
  when 'channel_title'  then 'atom:source/atom:title'
  when 'channel_title_plain' then 'atom:title/text()'
  when 'date'           then 'atom:updated/@planet:format'
  when 'feed'           then "atom:link[@rel='self']/@href"
  when 'feedtype'       then "atom:link[@rel='self']/@type"
  when 'generator'      then 'atom:generator'
  when 'link'           then "atom:link[@rel='alternate']/@href"
  when 'name'           then 'atom:title'
  when 'owner_name'     then 'atom:author/atom:name'
  when 'title'          then 'atom:title'
  when 'url'            then "atom:link[@rel='alternate']/@href"

  when /^channel_/      then "atom:source/planet:#{name.split('_',2).last}"

  when 'new_date'       then
    "substring-before(atom:updated/@planet:format,', ')}, {" +
    "substring-before(substring-after(atom:updated/@planet:format,', '), ' ')"

  else
    STDERR.puts "Unknown variable encountered: #{name}"
    name
  end
end

# kill the DOCTYPE
tmpl.sub! /<!DOCTYPE.*?>\s*/, ''

# enclose line comments in XML/HTML comments
tmpl.gsub! /^((#.*\n)+)/, "<!--\n\\1-->\n"

# special case: feed type already is formatted as a mime type
tmpl.gsub! 'application/<TMPL_VAR feedtype>+xml', '<TMPL_VAR feedtype>'

# template variables
tmpl.gsub! /<TMPL_VAR (\w+) ESCAPE="HTML">/, '<TMPL_VAR \1>'
tmpl.gsub! /<TMPL_VAR (\w+)>/ do
  if $1 == 'content'
    '<choose></choose>'
  else
   "{#{xpath.call($1)}}"
  end
end

# template if statements temporarily become pseudo-span elements
tmpl.gsub! /<\/TMPL_IF>/, '</span>'
tmpl.gsub! /<TMPL_IF (\w+)>/ do
  if $1 == 'new_date'
    '<span test="not(' +
        'preceding-sibling::atom:entry[substring(atom:updated,1,10) =' +
        'substring(atom:updated,1,10)])">'

  elsif $1 == 'new_channel'
    '<span test="not(' +
        'preceding-sibling::atom:entry/atom:source/atom:id =' +
        'atom:source/atom:id)">'

  else
    "<span test=\"#{xpath.call($1)}\">"
  end
end

# template loop statements temporarily become pseudo-span elements
tmpl.gsub! /<\/TMPL_LOOP>/, '</span>'
tmpl.gsub! /<TMPL_LOOP (\w+)>/ do
  "<span select=\"#{xpath.call($1)}\">"
end

# convert template to DOM
doc = HTML5.parse(tmpl)

# reparent conditional head elements
doc.elements.each('html/body/span[meta or link]') {|span|
  doc.elements['html/head'] << span
}

doc.elements.each('//*') do |node|
  # pseudo span elements become xsl control elements
  if node.name == 'span'
    if node.attributes['select']
      node.name = 'xsl:for-each'
    elsif node.attributes['test']
      node.name = 'xsl:if'
    end
  end

  # choose between content and summary
  if node.name == 'choose'
    node.name = 'xsl:choose'
    child = node.add_element('xsl:when', 'test' => 'atom:content')
    child.add_element('xsl:apply-templates', 'select' => 'atom:content')
    child = node.add_element('xsl:when', 'test' => 'atom:summary')
    child.add_element('xsl:apply-templates', 'select' => 'atom:summary')
  end

  # convert scripts to CDATA
  if node.name == 'script'
    node.texts.each do |text|
      if text.value =~ /[&<]/
        text.previous_sibling = REXML::CData.new(text.value)
        text.remove
      end
    end
  end

  # add namespace to html element
  if node.name == 'html'
    node.add_namespace 'http://www.w3.org/1999/xhtml'
  end

  # replace string interpretation in text nodes with xsl:value of elements
  node.texts.each do |text|
    if text.value =~ /\{.*?\}/
      text.value.split(/\{(.*?)\}/).each_with_index do |value, index|
        if index % 2 == 1
          text.previous_sibling = REXML::Element.new('xsl:value-of')
          text.previous_sibling.attributes['select'] = value
        elsif !value.empty?
          text.previous_sibling = REXML::Text.new(value)
        end
      end
      text.remove
    end
  end
end

# Egregious hack: convert all escaped single quotes in XPath
# expressions to double quotes.
tmpl = doc.to_s.gsub /\{.*?\}| (test|select)='.*?'/ do |xpath|
  xpath.gsub('&apos;','"')
end

# wrapt the template in a stylesheet
xslt = REXML::Document.new <<EOF
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"
                xmlns:atom="http://www.w3.org/2005/Atom"
                xmlns:xhtml="http://www.w3.org/1999/xhtml"
                xmlns:planet="http://planet.intertwingly.net/"
                xmlns="http://www.w3.org/1999/xhtml"
                exclude-result-prefixes="atom planet xhtml">

<xsl:output method="xml" omit-xml-declaration="yes"/>

<!-- main template -->
<xsl:template match="atom:feed">
#{tmpl.gsub(/\n\n\n+/,"\n\n")}
</xsl:template>

<!-- primary template -->
<xsl:template match="atom:content/xhtml:div | atom:summary/xhtml:div">
  <xsl:copy>
    <xsl:if test="../@xml:lang and not(../@xml:lang = ../../@xml:lang)">
      <xsl:attribute name="xml:lang">
        <xsl:value-of select="../@xml:lang"/>
      </xsl:attribute>
    </xsl:if>
    <xsl:attribute name="class">content</xsl:attribute>
    <xsl:apply-templates select="@*|node()"/>
  </xsl:copy>
</xsl:template>

<!-- plain text content -->
<xsl:template match="atom:content/text() | atom:summary/text()">
  <div class="content" xmlns="http://www.w3.org/1999/xhtml">
    <xsl:if test="../@xml:lang and not(../@xml:lang = ../../@xml:lang)">
      <xsl:attribute name="xml:lang">
        <xsl:value-of select="../@xml:lang"/>
      </xsl:attribute>
    </xsl:if>
    <xsl:copy-of select="."/>
  </div>
</xsl:template>

<!-- Remove stray atom elements -->
<xsl:template match="atom:*">
  <xsl:apply-templates/>
</xsl:template>

<!-- pass through everything else -->
<xsl:template match="@*|node()">
  <xsl:copy>
    <xsl:apply-templates select="@*|node()"/>
  </xsl:copy>
</xsl:template>

</xsl:stylesheet>

EOF

# output stylesheet
open(ARGV.first.sub(/.tmpl$/,'.xslt'),'w') do |file|
  file.write xslt.to_s.gsub('&quot;','"')
end