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TemplateInspector.php
001 <?php
002
003 /**
004 * @package s9e\TextFormatter
005 * @copyright Copyright (c) 2010-2022 The s9e authors
006 * @license http://www.opensource.org/licenses/mit-license.php The MIT License
007 */
008 namespace s9e\TextFormatter\Configurator\Helpers;
009
010 use DOMElement;
011 use DOMXPath;
012
013 /**
014 * This class helps the RulesGenerator by analyzing a given template in order to answer questions
015 * such as "can this tag be a child/descendant of that other tag?" and others related to the HTML5
016 * content model.
017 *
018 * We use the HTML5 specs to determine which children or descendants should be allowed or denied
019 * based on HTML5 content models. While it does not exactly match HTML5 content models, it gets
020 * pretty close. We also use HTML5 "optional end tag" rules to create closeParent rules.
021 *
022 * Currently, this method does not evaluate elements created with <xsl:element> correctly, or
023 * attributes created with <xsl:attribute> and may never will due to the increased complexity it
024 * would entail. Additionally, it does not evaluate the scope of <xsl:apply-templates/>. For
025 * instance, it will treat <xsl:apply-templates select="LI"/> as if it was <xsl:apply-templates/>
026 *
027 * @link http://dev.w3.org/html5/spec/content-models.html#content-models
028 * @link http://dev.w3.org/html5/spec/syntax.html#optional-tags
029 */
030 class TemplateInspector
031 {
032 /**
033 * XSL namespace
034 */
035 const XMLNS_XSL = 'http://www.w3.org/1999/XSL/Transform';
036
037 /**
038 * @var string[] allowChild bitfield for each branch
039 */
040 protected $allowChildBitfields = [];
041
042 /**
043 * @var bool Whether elements are allowed as children
044 */
045 protected $allowsChildElements;
046
047 /**
048 * @var bool Whether text nodes are allowed as children
049 */
050 protected $allowsText;
051
052 /**
053 * @var array[] Array of array of DOMElement instances
054 */
055 protected $branches;
056
057 /**
058 * @var string OR-ed bitfield representing all of the categories used by this template
059 */
060 protected $contentBitfield = "\0";
061
062 /**
063 * @var string Default bitfield used at the root of a branch
064 */
065 protected $defaultBranchBitfield;
066
067 /**
068 * @var string denyDescendant bitfield
069 */
070 protected $denyDescendantBitfield = "\0";
071
072 /**
073 * @var \DOMDocument Document containing the template
074 */
075 protected $dom;
076
077 /**
078 * @var bool Whether this template contains any HTML elements
079 */
080 protected $hasElements = false;
081
082 /**
083 * @var bool Whether this template renders non-whitespace text nodes at its root
084 */
085 protected $hasRootText;
086
087 /**
088 * @var bool Whether this template should be considered a block-level element
089 */
090 protected $isBlock = false;
091
092 /**
093 * @var bool Whether the template uses the "empty" content model
094 */
095 protected $isEmpty;
096
097 /**
098 * @var bool Whether this template adds to the list of active formatting elements
099 */
100 protected $isFormattingElement;
101
102 /**
103 * @var bool Whether this template lets content through via an xsl:apply-templates element
104 */
105 protected $isPassthrough = false;
106
107 /**
108 * @var bool Whether all branches use the transparent content model
109 */
110 protected $isTransparent = false;
111
112 /**
113 * @var bool Whether all branches have an ancestor that is a void element
114 */
115 protected $isVoid;
116
117 /**
118 * @var array Last HTML element that precedes an <xsl:apply-templates/> node
119 */
120 protected $leafNodes = [];
121
122 /**
123 * @var bool Whether any branch has an element that preserves new lines by default (e.g. <pre>)
124 */
125 protected $preservesNewLines = false;
126
127 /**
128 * @var array Bitfield of the first HTML element of every branch
129 */
130 protected $rootBitfields = [];
131
132 /**
133 * @var array Every HTML element that has no HTML parent
134 */
135 protected $rootNodes = [];
136
137 /**
138 * @var DOMXPath XPath engine associated with $this->dom
139 */
140 protected $xpath;
141
142 /**
143 * Constructor
144 *
145 * @param string $template Template content
146 */
147 public function __construct($template)
148 {
149 $this->dom = TemplateLoader::load($template);
150 $this->xpath = new DOMXPath($this->dom);
151
152 $this->defaultBranchBitfield = ElementInspector::getAllowChildBitfield($this->dom->createElement('div'));
153
154 $this->analyseRootNodes();
155 $this->analyseBranches();
156 $this->analyseContent();
157 }
158
159 /**
160 * Return whether this template allows a given child
161 *
162 * @param TemplateInspector $child
163 * @return bool
164 */
165 public function allowsChild(TemplateInspector $child)
166 {
167 // Sometimes, a template can technically be allowed as a child but denied as a descendant
168 if (!$this->allowsDescendant($child))
169 {
170 return false;
171 }
172
173 foreach ($child->rootBitfields as $rootBitfield)
174 {
175 foreach ($this->allowChildBitfields as $allowChildBitfield)
176 {
177 if (!self::match($rootBitfield, $allowChildBitfield))
178 {
179 return false;
180 }
181 }
182 }
183
184 return ($this->allowsText || !$child->hasRootText);
185 }
186
187 /**
188 * Return whether this template allows a given descendant
189 *
190 * @param TemplateInspector $descendant
191 * @return bool
192 */
193 public function allowsDescendant(TemplateInspector $descendant)
194 {
195 // Test whether the descendant is explicitly disallowed
196 if (self::match($descendant->contentBitfield, $this->denyDescendantBitfield))
197 {
198 return false;
199 }
200
201 // Test whether the descendant contains any elements and we disallow elements
202 return ($this->allowsChildElements || !$descendant->hasElements);
203 }
204
205 /**
206 * Return whether this template allows elements as children
207 *
208 * @return bool
209 */
210 public function allowsChildElements()
211 {
212 return $this->allowsChildElements;
213 }
214
215 /**
216 * Return whether this template allows text nodes as children
217 *
218 * @return bool
219 */
220 public function allowsText()
221 {
222 return $this->allowsText;
223 }
224
225 /**
226 * Return whether this template automatically closes given parent template
227 *
228 * @param TemplateInspector $parent
229 * @return bool
230 */
231 public function closesParent(TemplateInspector $parent)
232 {
233 // Test whether any of this template's root nodes closes any of given template's leaf nodes
234 foreach ($this->rootNodes as $rootNode)
235 {
236 foreach ($parent->leafNodes as $leafNode)
237 {
238 if (ElementInspector::closesParent($rootNode, $leafNode))
239 {
240 return true;
241 }
242 }
243 }
244
245 return false;
246 }
247
248 /**
249 * Evaluate an XPath expression
250 *
251 * @param string $expr XPath expression
252 * @param DOMElement $node Context node
253 * @return mixed
254 */
255 public function evaluate($expr, DOMElement $node = null)
256 {
257 return $this->xpath->evaluate($expr, $node);
258 }
259
260 /**
261 * Return whether this template should be considered a block-level element
262 *
263 * @return bool
264 */
265 public function isBlock()
266 {
267 return $this->isBlock;
268 }
269
270 /**
271 * Return whether this template adds to the list of active formatting elements
272 *
273 * @return bool
274 */
275 public function isFormattingElement()
276 {
277 return $this->isFormattingElement;
278 }
279
280 /**
281 * Return whether this template uses the "empty" content model
282 *
283 * @return bool
284 */
285 public function isEmpty()
286 {
287 return $this->isEmpty;
288 }
289
290 /**
291 * Return whether this template lets content through via an xsl:apply-templates element
292 *
293 * @return bool
294 */
295 public function isPassthrough()
296 {
297 return $this->isPassthrough;
298 }
299
300 /**
301 * Return whether this template uses the "transparent" content model
302 *
303 * @return bool
304 */
305 public function isTransparent()
306 {
307 return $this->isTransparent;
308 }
309
310 /**
311 * Return whether all branches have an ancestor that is a void element
312 *
313 * @return bool
314 */
315 public function isVoid()
316 {
317 return $this->isVoid;
318 }
319
320 /**
321 * Return whether this template preserves the whitespace in its descendants
322 *
323 * @return bool
324 */
325 public function preservesNewLines()
326 {
327 return $this->preservesNewLines;
328 }
329
330 /**
331 * Analyses the content of the whole template and set $this->contentBitfield accordingly
332 */
333 protected function analyseContent()
334 {
335 // Get all non-XSL elements
336 $query = '//*[namespace-uri() != "' . self::XMLNS_XSL . '"]';
337 foreach ($this->xpath->query($query) as $node)
338 {
339 $this->contentBitfield |= ElementInspector::getCategoryBitfield($node);
340 $this->hasElements = true;
341 }
342
343 // Test whether this template is passthrough
344 $this->isPassthrough = (bool) $this->evaluate('count(//xsl:apply-templates)');
345 }
346
347 /**
348 * Records the HTML elements (and their bitfield) rendered at the root of the template
349 */
350 protected function analyseRootNodes()
351 {
352 // Get every non-XSL element with no non-XSL ancestor. This should return us the first
353 // HTML element of every branch
354 $query = '//*[namespace-uri() != "' . self::XMLNS_XSL . '"]'
355 . '[not(ancestor::*[namespace-uri() != "' . self::XMLNS_XSL . '"])]';
356 foreach ($this->xpath->query($query) as $node)
357 {
358 // Store the root node of this branch
359 $this->rootNodes[] = $node;
360
361 // If any root node is a block-level element, we'll mark the template as such
362 if ($this->elementIsBlock($node))
363 {
364 $this->isBlock = true;
365 }
366
367 $this->rootBitfields[] = ElementInspector::getCategoryBitfield($node);
368 }
369
370 // Test for non-whitespace text nodes at the root. For that we need a predicate that filters
371 // out: nodes with a non-XSL ancestor,
372 $predicate = '[not(ancestor::*[namespace-uri() != "' . self::XMLNS_XSL . '"])]';
373
374 // ..and nodes with an <xsl:attribute/>, <xsl:comment/> or <xsl:variable/> ancestor
375 $predicate .= '[not(ancestor::xsl:attribute | ancestor::xsl:comment | ancestor::xsl:variable)]';
376
377 $query = '//text()[normalize-space() != ""]' . $predicate
378 . '|'
379 . '//xsl:text[normalize-space() != ""]' . $predicate
380 . '|'
381 . '//xsl:value-of' . $predicate;
382
383 $this->hasRootText = (bool) $this->evaluate('count(' . $query . ')');
384 }
385
386 /**
387 * Analyses each branch that leads to an <xsl:apply-templates/> tag
388 */
389 protected function analyseBranches()
390 {
391 $this->branches = [];
392 foreach ($this->xpath->query('//xsl:apply-templates') as $applyTemplates)
393 {
394 $query = 'ancestor::*[namespace-uri() != "' . self::XMLNS_XSL . '"]';
395 $this->branches[] = iterator_to_array($this->xpath->query($query, $applyTemplates));
396 }
397
398 $this->computeAllowsChildElements();
399 $this->computeAllowsText();
400 $this->computeBitfields();
401 $this->computeFormattingElement();
402 $this->computeIsEmpty();
403 $this->computeIsTransparent();
404 $this->computeIsVoid();
405 $this->computePreservesNewLines();
406 $this->storeLeafNodes();
407 }
408
409 /**
410 * Test whether any branch of this template has an element that has given property
411 *
412 * @param string $methodName
413 * @return bool
414 */
415 protected function anyBranchHasProperty($methodName)
416 {
417 foreach ($this->branches as $branch)
418 {
419 foreach ($branch as $element)
420 {
421 if (ElementInspector::$methodName($element))
422 {
423 return true;
424 }
425 }
426 }
427
428 return false;
429 }
430
431 /**
432 * Compute the allowChildBitfields and denyDescendantBitfield properties
433 *
434 * @return void
435 */
436 protected function computeBitfields()
437 {
438 if (empty($this->branches))
439 {
440 $this->allowChildBitfields = ["\0"];
441
442 return;
443 }
444 foreach ($this->branches as $branch)
445 {
446 /**
447 * @var string allowChild bitfield for current branch. Starts with the value associated
448 * with <div> in order to approximate a value if the whole branch uses the
449 * transparent content model
450 */
451 $branchBitfield = $this->defaultBranchBitfield;
452
453 foreach ($branch as $element)
454 {
455 if (!ElementInspector::isTransparent($element))
456 {
457 // If the element isn't transparent, we reset its bitfield
458 $branchBitfield = "\0";
459 }
460
461 // allowChild rules are cumulative if transparent, and reset above otherwise
462 $branchBitfield |= ElementInspector::getAllowChildBitfield($element);
463
464 // denyDescendant rules are cumulative
465 $this->denyDescendantBitfield |= ElementInspector::getDenyDescendantBitfield($element);
466 }
467
468 // Add this branch's bitfield to the list
469 $this->allowChildBitfields[] = $branchBitfield;
470 }
471 }
472
473 /**
474 * Compute the allowsChildElements property
475 *
476 * A template allows child Elements if it has at least one xsl:apply-templates and none of its
477 * ancestors have the text-only ("to") property
478 *
479 * @return void
480 */
481 protected function computeAllowsChildElements()
482 {
483 $this->allowsChildElements = ($this->anyBranchHasProperty('isTextOnly')) ? false : !empty($this->branches);
484 }
485
486 /**
487 * Compute the allowsText property
488 *
489 * A template is said to allow text if none of the leaf elements disallow text
490 *
491 * @return void
492 */
493 protected function computeAllowsText()
494 {
495 foreach (array_filter($this->branches) as $branch)
496 {
497 if (ElementInspector::disallowsText(end($branch)))
498 {
499 $this->allowsText = false;
500
501 return;
502 }
503 }
504 $this->allowsText = true;
505 }
506
507 /**
508 * Compute the isFormattingElement property
509 *
510 * A template is said to be a formatting element if all (non-zero) of its branches are entirely
511 * composed of formatting elements
512 *
513 * @return void
514 */
515 protected function computeFormattingElement()
516 {
517 foreach ($this->branches as $branch)
518 {
519 foreach ($branch as $element)
520 {
521 if (!ElementInspector::isFormattingElement($element) && !$this->isFormattingSpan($element))
522 {
523 $this->isFormattingElement = false;
524
525 return;
526 }
527 }
528 }
529 $this->isFormattingElement = (bool) count(array_filter($this->branches));
530 }
531
532 /**
533 * Compute the isEmpty property
534 *
535 * A template is said to be empty if it has no xsl:apply-templates elements or any there is a empty
536 * element ancestor to an xsl:apply-templates element
537 *
538 * @return void
539 */
540 protected function computeIsEmpty()
541 {
542 $this->isEmpty = ($this->anyBranchHasProperty('isEmpty')) || empty($this->branches);
543 }
544
545 /**
546 * Compute the isTransparent property
547 *
548 * A template is said to be transparent if it has at least one branch and no non-transparent
549 * elements in its path
550 *
551 * @return void
552 */
553 protected function computeIsTransparent()
554 {
555 foreach ($this->branches as $branch)
556 {
557 foreach ($branch as $element)
558 {
559 if (!ElementInspector::isTransparent($element))
560 {
561 $this->isTransparent = false;
562
563 return;
564 }
565 }
566 }
567 $this->isTransparent = !empty($this->branches);
568 }
569
570 /**
571 * Compute the isVoid property
572 *
573 * A template is said to be void if it has no xsl:apply-templates elements or any there is a void
574 * element ancestor to an xsl:apply-templates element
575 *
576 * @return void
577 */
578 protected function computeIsVoid()
579 {
580 $this->isVoid = ($this->anyBranchHasProperty('isVoid')) || empty($this->branches);
581 }
582
583 /**
584 * Compute the preservesNewLines property
585 *
586 * @return void
587 */
588 protected function computePreservesNewLines()
589 {
590 foreach ($this->branches as $branch)
591 {
592 $style = '';
593 foreach ($branch as $element)
594 {
595 $style .= $this->getStyle($element, true);
596 }
597
598 if (preg_match('(.*white-space\\s*:\\s*(no|pre))is', $style, $m) && strtolower($m[1]) === 'pre')
599 {
600 $this->preservesNewLines = true;
601
602 return;
603 }
604 }
605 $this->preservesNewLines = false;
606 }
607
608 /**
609 * Test whether given element is a block-level element
610 *
611 * @param DOMElement $element
612 * @return bool
613 */
614 protected function elementIsBlock(DOMElement $element)
615 {
616 $style = $this->getStyle($element);
617 if (preg_match('(\\bdisplay\\s*:\\s*block)i', $style))
618 {
619 return true;
620 }
621 if (preg_match('(\\bdisplay\\s*:\\s*(?:inli|no)ne)i', $style))
622 {
623 return false;
624 }
625
626 return ElementInspector::isBlock($element);
627 }
628
629 /**
630 * Retrieve and return the inline style assigned to given element
631 *
632 * @param DOMElement $node Context node
633 * @param bool $deep Whether to retrieve the content of all xsl:attribute descendants
634 * @return string
635 */
636 protected function getStyle(DOMElement $node, $deep = false)
637 {
638 $style = '';
639 if (ElementInspector::preservesWhitespace($node))
640 {
641 $style .= 'white-space:pre;';
642 }
643 $style .= $node->getAttribute('style');
644
645 // Add the content of any descendant/child xsl:attribute named "style"
646 $query = (($deep) ? './/' : './') . 'xsl:attribute[@name="style"]';
647 foreach ($this->xpath->query($query, $node) as $attribute)
648 {
649 $style .= ';' . $attribute->textContent;
650 }
651
652 return $style;
653 }
654
655 /**
656 * Test whether given node is a span element used for formatting
657 *
658 * Will return TRUE if the node is a span element with a class attribute and/or a style attribute
659 * and no other attributes
660 *
661 * @param DOMElement $node
662 * @return boolean
663 */
664 protected function isFormattingSpan(DOMElement $node)
665 {
666 if ($node->nodeName !== 'span')
667 {
668 return false;
669 }
670
671 if ($node->getAttribute('class') === '' && $node->getAttribute('style') === '')
672 {
673 return false;
674 }
675
676 foreach ($node->attributes as $attrName => $attribute)
677 {
678 if ($attrName !== 'class' && $attrName !== 'style')
679 {
680 return false;
681 }
682 }
683
684 return true;
685 }
686
687 /**
688 * Store the names of every leaf node
689 *
690 * A leaf node is defined as the closest non-XSL ancestor to an xsl:apply-templates element
691 *
692 * @return void
693 */
694 protected function storeLeafNodes()
695 {
696 foreach (array_filter($this->branches) as $branch)
697 {
698 $this->leafNodes[] = end($branch);
699 }
700 }
701
702 /**
703 * Test whether two bitfields have any bits in common
704 *
705 * @param string $bitfield1
706 * @param string $bitfield2
707 * @return bool
708 */
709 protected static function match($bitfield1, $bitfield2)
710 {
711 return (trim($bitfield1 & $bitfield2, "\0") !== '');
712 }
713 }