TemplateParser::removeNodes() - Code Metrics - Inspection of "TemplateParser: simplified node removal" - s9e/TextFormatter - Measure and Improve Code Quality continuously with Scrutinizer

Completed
Push — master ( 75e09b...8a3237 )

by Josh
created 2018-01-24 17:48 UTC
TemplateParser::removeNodes() A

↳ Parent: TemplateParser
Complexity

Conditions	3
Paths	3
Size

Total Lines	11
Code Lines	5
Duplication

Lines	0
Ratio	0 %
Importance

Changes
Metric	Value
dl	0
loc	11
rs	9.4285
c	0
b	0
f	0
cc	3
eloc	5
nc	3
nop	3
<?php

/**
* @package   s9e\TextFormatter
* @copyright Copyright (c) 2010-2018 The s9e Authors
* @license   http://www.opensource.org/licenses/mit-license.php The MIT License
*/
namespace s9e\TextFormatter\Configurator\Helpers;

use DOMDocument;
use DOMElement;
use DOMNode;
use DOMXPath;
use RuntimeException;

class TemplateParser
{
	/**
	* XSL namespace
	*/
	const XMLNS_XSL = 'http://www.w3.org/1999/XSL/Transform';

	/**
	* @var string Regexp that matches the names of all void elements
	* @link http://www.w3.org/TR/html-markup/syntax.html#void-elements
	*/
	public static $voidRegexp = '/^(?:area|base|br|col|command|embed|hr|img|input|keygen|link|meta|param|source|track|wbr)$/Di';

	/**
	* Parse a template into an internal representation
	*
	* @param  string      $template     Source template
	* @return DOMDocument               Internal representation
	*/
	public static function parse($template)
	{
		$xsl = '<xsl:template xmlns:xsl="' . self::XMLNS_XSL . '">' . $template . '</xsl:template>';

		$dom = new DOMDocument;
		$dom->loadXML($xsl);

		$ir = new DOMDocument;
		$ir->loadXML('<template/>');

		self::parseChildren($ir->documentElement, $dom->documentElement);
		self::normalize($ir);

		return $ir;
	}

	/**
	* Parse an XPath expression that is composed entirely of equality tests between a variable part
	* and a constant part
	*
	* @param  string      $expr
	* @return array|false
	*/
	public static function parseEqualityExpr($expr)
	{
		// Match an equality between a variable and a literal or the concatenation of strings
		$eq = '(?<equality>'
		    . '(?<key>@[-\\w]+|\\$\\w+|\\.)'
		    . '(?<operator>\\s*=\\s*)'
		    . '(?:'
		    . '(?<literal>(?<string>"[^"]*"|\'[^\']*\')|0|[1-9][0-9]*)'
		    . '|'
		    . '(?<concat>concat\\(\\s*(?&string)\\s*(?:,\\s*(?&string)\\s*)+\\))'
		    . ')'
		    . '|'
		    . '(?:(?<literal>(?&literal))|(?<concat>(?&concat)))(?&operator)(?<key>(?&key))'
		    . ')';

		// Match a string that is entirely composed of equality checks separated with "or"
		$regexp = '(^(?J)\\s*' . $eq . '\\s*(?:or\\s*(?&equality)\\s*)*$)';

		if (!preg_match($regexp, $expr))
		{
			return false;
		}

		preg_match_all("((?J)$eq)", $expr, $matches, PREG_SET_ORDER);

		$map = [];
		foreach ($matches as $m)
		{
			$key = $m['key'];
			if (!empty($m['concat']))
			{
				preg_match_all('(\'[^\']*\'|"[^"]*")', $m['concat'], $strings);

				$value = '';
				foreach ($strings[0] as $string)
				{
					$value .= substr($string, 1, -1);
				}
			}
			else
			{
				$value = $m['literal'];
				if ($value[0] === "'" || $value[0] === '"')
				{
					$value = substr($value, 1, -1);
				}
			}

			$map[$key][] = $value;
		}

		return $map;
	}

	//==========================================================================
	// General parsing
	//==========================================================================

	/**
	* Parse all the children of a given element
	*
	* @param  DOMElement $ir     Node in the internal representation that represents the parent node
	* @param  DOMElement $parent Parent node
	* @return void
	*/
	protected static function parseChildren(DOMElement $ir, DOMElement $parent)
	{
		foreach ($parent->childNodes as $child)
		{
			switch ($child->nodeType)
			{
				case XML_COMMENT_NODE:
					// Do nothing
					break;

				case XML_TEXT_NODE:
					if (trim($child->textContent) !== '')
					{
						self::appendOutput($ir, 'literal', $child->textContent);
					}
					break;

				case XML_ELEMENT_NODE:
					self::parseNode($ir, $child);
					break;

				default:
					throw new RuntimeException("Cannot parse node '" . $child->nodeName . "''");
			}
		}
	}

	/**
	* Parse a given node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node Node to parse
	* @return void
	*/
	protected static function parseNode(DOMElement $ir, DOMElement $node)
	{
		// XSL elements are parsed by the corresponding parseXsl* method
		if ($node->namespaceURI === self::XMLNS_XSL)
		{
			$methodName = 'parseXsl' . str_replace(' ', '', ucwords(str_replace('-', ' ', $node->localName)));

			if (!method_exists(__CLASS__, $methodName))
			{
				throw new RuntimeException("Element '" . $node->nodeName . "' is not supported");
			}

			return self::$methodName($ir, $node);
		}

		// Create an <element/> with a name attribute equal to given node's name
		$element = self::appendElement($ir, 'element');
		$element->setAttribute('name', $node->nodeName);

		// Append an <attribute/> element for each namespace declaration
		$xpath = new DOMXPath($node->ownerDocument);
		foreach ($xpath->query('namespace::*', $node) as $ns)
		{
			if ($node->hasAttribute($ns->nodeName))
			{
				$irAttribute = self::appendElement($element, 'attribute');
				$irAttribute->setAttribute('name', $ns->nodeName);
				self::appendOutput($irAttribute, 'literal', $ns->nodeValue);
			}
		}

		// Append an <attribute/> element for each of this node's attribute
		foreach ($node->attributes as $attribute)
		{
			$irAttribute = self::appendElement($element, 'attribute');
			$irAttribute->setAttribute('name', $attribute->nodeName);

			// Append an <output/> element to represent the attribute's value
			self::appendOutput($irAttribute, 'avt', $attribute->value);
		}

		// Parse the content of this node
		self::parseChildren($element, $node);
	}

	//==========================================================================
	// XSL parsing
	//==========================================================================

	/**
	* Parse an <xsl:apply-templates/> node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:apply-templates/> node
	* @return void
	*/
	protected static function parseXslApplyTemplates(DOMElement $ir, DOMElement $node)
	{
		$applyTemplates = self::appendElement($ir, 'applyTemplates');

		if ($node->hasAttribute('select'))
		{
			$applyTemplates->setAttribute(
				'select',
				$node->getAttribute('select')
			);
		}
	}

	/**
	* Parse an <xsl:attribute/> node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:attribute/> node
	* @return void
	*/
	protected static function parseXslAttribute(DOMElement $ir, DOMElement $node)
	{
		$attrName = $node->getAttribute('name');

		if ($attrName !== '')
		{
			$attribute = self::appendElement($ir, 'attribute');

			// Copy this attribute's name
			$attribute->setAttribute('name', $attrName);

			// Parse this attribute's content
			self::parseChildren($attribute, $node);
		}
	}

	/**
	* Parse an <xsl:choose/> node and its <xsl:when/> and <xsl:otherwise/> children into the
	* internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:choose/> node
	* @return void
	*/
	protected static function parseXslChoose(DOMElement $ir, DOMElement $node)
	{
		$switch = self::appendElement($ir, 'switch');

		foreach ($node->getElementsByTagNameNS(self::XMLNS_XSL, 'when') as $when)
		{
			// Only children of current node, exclude other descendants
			if ($when->parentNode !== $node)
			{
				continue;
			}

			// Create a <case/> element with the original test condition in @test
			$case = self::appendElement($switch, 'case');
			$case->setAttribute('test', $when->getAttribute('test'));

			// Parse this branch's content
			self::parseChildren($case, $when);
		}

		// Add the default branch, which is presumed to be last
		foreach ($node->getElementsByTagNameNS(self::XMLNS_XSL, 'otherwise') as $otherwise)
		{
			// Only children of current node, exclude other descendants
			if ($otherwise->parentNode !== $node)
			{
				continue;
			}

			$case = self::appendElement($switch, 'case');

			// Parse this branch's content
			self::parseChildren($case, $otherwise);

			// There should be only one <xsl:otherwise/> but we'll break anyway
			break;
		}
	}

	/**
	* Parse an <xsl:comment/> node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:comment/> node
	* @return void
	*/
	protected static function parseXslComment(DOMElement $ir, DOMElement $node)
	{
		$comment = self::appendElement($ir, 'comment');

		// Parse this branch's content
		self::parseChildren($comment, $node);
	}

	/**
	* Parse an <xsl:copy-of/> node into the internal representation
	*
	* NOTE: only attributes are supported
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:copy-of/> node
	* @return void
	*/
	protected static function parseXslCopyOf(DOMElement $ir, DOMElement $node)
	{
		$expr = $node->getAttribute('select');

		// <xsl:copy-of select="@foo"/>
		if (preg_match('#^@([-\\w]+)$#', $expr, $m))
		{
			// Create a switch element in the IR
			$switch = self::appendElement($ir, 'switch');
			$case   = self::appendElement($switch, 'case');
			$case->setAttribute('test', $expr);

			// Append an attribute element
			$attribute = self::appendElement($case, 'attribute');
			$attribute->setAttribute('name', $m[1]);

			// Set the attribute's content, which is simply the copied attribute's value
			self::appendOutput($attribute, 'xpath', $expr);

			return;
		}

		// <xsl:copy-of select="@*"/>
		if ($expr === '@*')
		{
			self::appendElement($ir, 'copyOfAttributes');

			return;
		}

		throw new RuntimeException("Unsupported <xsl:copy-of/> expression '" . $expr . "'");
	}

	/**
	* Parse an <xsl:element/> node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:element/> node
	* @return void
	*/
	protected static function parseXslElement(DOMElement $ir, DOMElement $node)
	{
		$elName = $node->getAttribute('name');

		if ($elName !== '')
		{
			$element = self::appendElement($ir, 'element');

			// Copy this element's name
			$element->setAttribute('name', $elName);

			// Parse this element's content
			self::parseChildren($element, $node);
		}
	}

	/**
	* Parse an <xsl:if/> node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:if/> node
	* @return void
	*/
	protected static function parseXslIf(DOMElement $ir, DOMElement $node)
	{
		// An <xsl:if/> is represented by a <switch/> with only one <case/>
		$switch = self::appendElement($ir, 'switch');
		$case   = self::appendElement($switch, 'case');
		$case->setAttribute('test', $node->getAttribute('test'));

		// Parse this branch's content
		self::parseChildren($case, $node);
	}

	/**
	* Parse an <xsl:text/> node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:text/> node
	* @return void
	*/
	protected static function parseXslText(DOMElement $ir, DOMElement $node)
	{
		self::appendOutput($ir, 'literal', $node->textContent);
	}

	/**
	* Parse an <xsl:value-of/> node into the internal representation
	*
	* @param  DOMElement $ir   Node in the internal representation that represents the node's parent
	* @param  DOMElement $node <xsl:value-of/> node
	* @return void
	*/
	protected static function parseXslValueOf(DOMElement $ir, DOMElement $node)
	{
		self::appendOutput($ir, 'xpath', $node->getAttribute('select'));
	}

	//==========================================================================
	// IR optimization
	//==========================================================================

	/**
	* Normalize an IR
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function normalize(DOMDocument $ir)
	{
		self::addDefaultCase($ir);
		self::addElementIds($ir);
		self::addCloseTagElements($ir);
		self::markEmptyElements($ir);
		self::optimize($ir);
		self::markConditionalCloseTagElements($ir);
		self::setOutputContext($ir);
		self::markBranchTables($ir);
	}

	/**
	* Add an empty default <case/> to <switch/> nodes that don't have one
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function addDefaultCase(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		foreach ($xpath->query('//switch[not(case[not(@test)])]') as $switch)
		{
			self::appendElement($switch, 'case');
		}
	}

	/**
	* Add an id attribute to <element/> nodes
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function addElementIds(DOMDocument $ir)
	{
		$id = 0;
		foreach ($ir->getElementsByTagName('element') as $element)
		{
			$element->setAttribute('id', ++$id);
		}
	}

	/**
	* Add <closeTag/> elements everywhere an open start tag should be closed
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function addCloseTagElements(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		$exprs = [
			'//applyTemplates[not(ancestor::attribute)]',
			'//comment',
			'//element',
			'//output[not(ancestor::attribute)]'
		];
		foreach ($xpath->query(implode('|', $exprs)) as $node)
		{
			$parentElementId = self::getParentElementId($node);
			if (isset($parentElementId))
			{
				$node->parentNode
				     ->insertBefore($ir->createElement('closeTag'), $node)
				     ->setAttribute('id', $parentElementId);
			}

			// Append a <closeTag/> to <element/> nodes to ensure that empty elements get closed
			if ($node->nodeName === 'element')
			{
				$id = $node->getAttribute('id');
				self::appendElement($node, 'closeTag')->setAttribute('id', $id);
			}
		}
	}

	/**
	* Mark conditional <closeTag/> nodes
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function markConditionalCloseTagElements(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		foreach ($ir->getElementsByTagName('closeTag') as $closeTag)
		{
			$id = $closeTag->getAttribute('id');

			// For each <switch/> ancestor, look for a <closeTag/> and that is either a sibling or
			// the descendant of a sibling, and that matches the id
			$query = 'ancestor::switch/'
			       . 'following-sibling::*/'
			       . 'descendant-or-self::closeTag[@id = "' . $id . '"]';
			foreach ($xpath->query($query, $closeTag) as $following)
			{
				// Mark following <closeTag/> nodes to indicate that the status of this tag must
				// be checked before it is closed
				$following->setAttribute('check', '');

				// Mark the current <closeTag/> to indicate that it must set a flag to indicate
				// that its tag has been closed
				$closeTag->setAttribute('set', '');
			}
		}
	}

	/**
	* Mark void elements and elements with no content
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function markEmptyElements(DOMDocument $ir)
	{
		foreach ($ir->getElementsByTagName('element') as $element)
		{
			// Test whether this element is (maybe) void
			$elName = $element->getAttribute('name');
			if (strpos($elName, '{') !== false)
			{
				// Dynamic element names must be checked at runtime
				$element->setAttribute('void', 'maybe');
			}
			elseif (preg_match(self::$voidRegexp, $elName))
			{
				// Static element names can be checked right now
				$element->setAttribute('void', 'yes');
			}

			// Find whether this element is empty
			$isEmpty = self::isEmpty($element);
			if ($isEmpty === 'yes' || $isEmpty === 'maybe')
			{
				$element->setAttribute('empty', $isEmpty);
			}
		}
	}

	/**
	* Get the context type for given output element
	*
	* @param  DOMNode $output
	* @return string
	*/
	protected static function getOutputContext(DOMNode $output)
	{
		$xpath = new DOMXPath($output->ownerDocument);
		if ($xpath->evaluate('boolean(ancestor::attribute)', $output))
		{
			return 'attribute';
		}

		if ($xpath->evaluate('boolean(ancestor::element[@name="script"])', $output))
		{
			return 'raw';
		}

		return 'text';
	}

	/**
	* Get the ID of the closest "element" ancestor
	*
	* @param  DOMNode     $node Context node
	* @return string|null
	*/
	protected static function getParentElementId(DOMNode $node)
	{
		$parentNode = $node->parentNode;
		while (isset($parentNode))
		{
			if ($parentNode->nodeName === 'element')
			{
				return $parentNode->getAttribute('id');
			}
			$parentNode = $parentNode->parentNode;
		}
	}

	/**
	* Fill in output context
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function setOutputContext(DOMDocument $ir)
	{
		foreach ($ir->getElementsByTagName('output') as $output)
		{
			$output->setAttribute('escape', self::getOutputContext($output));
		}
	}

	/**
	* Optimize an IR
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function optimize(DOMDocument $ir)
	{
		// Get a snapshot of current internal representation
		$xml = $ir->saveXML();

		// Set a maximum number of loops to ward against infinite loops
		$remainingLoops = 10;

		// From now on, keep looping until no further modifications are applied
		do
		{
			$old = $xml;
			self::optimizeCloseTagElements($ir);
			$xml = $ir->saveXML();
		}
		while (--$remainingLoops > 0 && $xml !== $old);

		self::removeCloseTagSiblings($ir);
		self::removeContentFromVoidElements($ir);
		self::mergeConsecutiveLiteralOutputElements($ir);
		self::removeEmptyDefaultCases($ir);
	}

	/**
	* Remove redundant closeTag siblings after a switch
	*
	* If all branches of a switch have a closeTag we can remove any closeTag siblings of the switch
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function removeCloseTagSiblings(DOMDocument $ir)
	{
		$query = '//switch[not(case[not(closeTag)])]/following-sibling::closeTag';
		self::removeNodes($ir, $query);
	}

	/**
	* Remove empty default cases (no test and no descendants)
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function removeEmptyDefaultCases(DOMDocument $ir)
	{
		$query = '//case[not(@test | node())]';
		self::removeNodes($ir, $query);
	}

	/**
	* Merge consecutive literal outputs
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function mergeConsecutiveLiteralOutputElements(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		foreach ($xpath->query('//output[@type="literal"]') as $output)
		{
			while ($output->nextSibling
				&& $output->nextSibling->nodeName === 'output'
				&& $output->nextSibling->getAttribute('type') === 'literal')
			{
				$output->nodeValue
					= htmlspecialchars($output->nodeValue . $output->nextSibling->nodeValue);
				$output->parentNode->removeChild($output->nextSibling);
			}
		}
	}

	/**
	* Optimize closeTags elements
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function optimizeCloseTagElements(DOMDocument $ir)
	{
		self::cloneCloseTagElementsIntoSwitch($ir);
		self::cloneCloseTagElementsOutOfSwitch($ir);
		self::removeRedundantCloseTagElementsInSwitch($ir);
		self::removeRedundantCloseTagElements($ir);
	}

	/**
	* Clone closeTag elements that follow a switch into said switch
	*
	* If there's a <closeTag/> right after a <switch/>, clone the <closeTag/> at the end of
	* the every <case/> that does not end with a <closeTag/>
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function cloneCloseTagElementsIntoSwitch(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		$query = '//switch[name(following-sibling::*) = "closeTag"]';
		foreach ($xpath->query($query) as $switch)
		{
			$closeTag = $switch->nextSibling;
			foreach ($switch->childNodes as $case)
			{
				if (!$case->lastChild || $case->lastChild->nodeName !== 'closeTag')
				{
					$case->appendChild($closeTag->cloneNode());
				}
			}
		}
	}

	/**
	* Clone closeTag elements from the head of a switch's cases before said switch
	*
	* If there's a <closeTag/> at the beginning of every <case/>, clone it and insert it
	* right before the <switch/> unless there's already one
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function cloneCloseTagElementsOutOfSwitch(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		$query = '//switch[not(preceding-sibling::closeTag)]';
		foreach ($xpath->query($query) as $switch)
		{
			foreach ($switch->childNodes as $case)
			{
				if (!$case->firstChild || $case->firstChild->nodeName !== 'closeTag')
				{
					// This case is either empty or does not start with a <closeTag/> so we skip
					// to the next <switch/>
					continue 2;
				}
			}
			// Insert the first child of the last <case/>, which should be the same <closeTag/>
			// as every other <case/>
			$switch->parentNode->insertBefore($switch->lastChild->firstChild->cloneNode(), $switch);
		}
	}

	/**
	* Remove all nodes that match given XPath query
	*
	* @param  DOMDocument $ir
	* @param  string      $query
	* @param  DOMNode     $contextNode
	* @return void
	*/
	protected static function removeNodes(DOMDocument $ir, $query, DOMNode $contextNode = null)
	{
		$xpath = new DOMXPath($ir);
		foreach ($xpath->query($query, $contextNode) as $node)
		{
			if ($node->parentNode instanceof DOMElement)
			{
				$node->parentNode->removeChild($node);
			}
		}
	}

	/**
	* Remove redundant closeTag elements from the tail of a switch's cases
	*
	* If there's a <closeTag/> right after a <switch/>, remove all <closeTag/> nodes at the
	* end of every <case/>
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function removeRedundantCloseTagElementsInSwitch(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		$query = '//switch[name(following-sibling::*) = "closeTag"]';
		foreach ($xpath->query($query) as $switch)
		{
			foreach ($switch->childNodes as $case)
			{
				while ($case->lastChild && $case->lastChild->nodeName === 'closeTag')
				{
					$case->removeChild($case->lastChild);
				}
			}
		}
	}

	/**
	* Remove redundant closeTag elements from the tail of a switch's cases
	*
	* For each <closeTag/> remove duplicate <closeTag/> nodes that are either siblings or
	* descendants of a sibling
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function removeRedundantCloseTagElements(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		foreach ($xpath->query('//closeTag') as $closeTag)
		{
			$id    = $closeTag->getAttribute('id');
			$query = 'following-sibling::*/descendant-or-self::closeTag[@id="' . $id . '"]';

			self::removeNodes($ir, $query, $closeTag);
		}
	}

	/**
	* Remove content from void elements
	*
	* For each void element, we find whichever <closeTag/> elements close it and remove everything
	* after
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function removeContentFromVoidElements(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);
		foreach ($xpath->query('//element[@void="yes"]') as $element)
		{
			$id    = $element->getAttribute('id');
			$query = './/closeTag[@id="' . $id . '"]/following-sibling::*';

			self::removeNodes($ir, $query, $element);
		}
	}

	/**
	* Mark switch elements that are used as branch tables
	*
	* If a switch is used for a series of equality tests against the same attribute or variable, the
	* attribute/variable is stored within the switch as "branch-key" and the values it is compared
	* against are stored JSON-encoded in the case as "branch-values". It can be used to create
	* optimized branch tables
	*
	* @param  DOMDocument $ir
	* @return void
	*/
	protected static function markBranchTables(DOMDocument $ir)
	{
		$xpath = new DOMXPath($ir);

		// Iterate over switch elements that have at least two case children with a test attribute
		foreach ($xpath->query('//switch[case[2][@test]]') as $switch)
		{
			$key = null;
			$branchValues = [];

			foreach ($switch->childNodes as $i => $case)
			{
				if (!$case->hasAttribute('test'))
				{
					continue;
				}

				$map = self::parseEqualityExpr($case->getAttribute('test'));

				// Test whether the expression matches an equality
				if ($map === false)
				{
					continue 2;
				}

				// Abort if there's more than 1 variable used
				if (count($map) !== 1)
				{
					continue 2;
				}

				// Test whether it uses the same key
				if (isset($key) && $key !== key($map))
				{
					continue 2;
				}

				$key = key($map);
				$branchValues[$i] = end($map);
			}

			$switch->setAttribute('branch-key', $key);
			foreach ($branchValues as $i => $values)
			{
				sort($values);
				$switch->childNodes->item($i)->setAttribute('branch-values', serialize($values));
			}
		}
	}

	//==========================================================================
	// Misc
	//==========================================================================

	/**
	* Create and append an element to given node in the IR
	*
	* @param  DOMElement $parentNode Parent node of the element
	* @param  string     $name       Tag name of the element
	* @param  string     $value      Value of the element
	* @return DOMElement             The created element
	*/
	protected static function appendElement(DOMElement $parentNode, $name, $value = '')
	{
		if ($value === '')
		{
			$element = $parentNode->ownerDocument->createElement($name);
		}
		else
		{
			$element = $parentNode->ownerDocument->createElement($name, $value);
		}

		$parentNode->appendChild($element);

		return $element;
	}

	/**
	* Append an <output/> element to given node in the IR
	*
	* @param  DOMElement $ir      Parent node
	* @param  string     $type    Either 'avt', 'literal' or 'xpath'
	* @param  string     $content Content to output
	* @return void
	*/
	protected static function appendOutput(DOMElement $ir, $type, $content)
	{
		// Reparse AVTs and add them as separate xpath/literal outputs
		if ($type === 'avt')
		{
			foreach (AVTHelper::parse($content) as $token)
			{
				$type = ($token[0] === 'expression') ? 'xpath' : 'literal';
				self::appendOutput($ir, $type, $token[1]);
			}

			return;
		}

		if ($type === 'xpath')
		{
			// Remove whitespace surrounding XPath expressions
			$content = trim($content);
		}

		if ($type === 'literal' && $content === '')
		{
			// Don't add empty literals
			return;
		}

		self::appendElement($ir, 'output', htmlspecialchars($content))
			->setAttribute('type', $type);
	}

	/**
	* Test whether given element will be empty at runtime (no content, no children)
	*
	* @param  DOMElement $ir Element in the IR
	* @return string         'yes', 'maybe' or 'no'
	*/
	protected static function isEmpty(DOMElement $ir)
	{
		$xpath = new DOMXPath($ir->ownerDocument);

		// Comments and elements count as not-empty and literal output is sure to output something
		if ($xpath->evaluate('count(comment | element | output[@type="literal"])', $ir))
		{
			return 'no';
		}

		// Test all branches of a <switch/>
		// NOTE: this assumes that <switch/> are normalized to always have a default <case/>
		$cases = [];
		foreach ($xpath->query('switch/case', $ir) as $case)
		{
			$cases[self::isEmpty($case)] = 1;
		}

		if (isset($cases['maybe']))
		{
			return 'maybe';
		}

		if (isset($cases['no']))
		{
			// If all the cases are not-empty, the element is not-empty
			if (!isset($cases['yes']))
			{
				return 'no';
			}

			// Some 'yes' and some 'no', the element is a 'maybe'
			return 'maybe';
		}

		// Test for <apply-templates/> or XPath output
		if ($xpath->evaluate('count(applyTemplates | output[@type="xpath"])', $ir))
		{
			// We can't know in advance whether those will produce output
			return 'maybe';
		}

		return 'yes';
	}
}
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