SMWQueryParser

Complexity

Total Complexity

112

Size/Duplication

Total Lines	603
Duplicated Lines	0 %

Coupling/Cohesion

Components	1
Dependencies	11

Test Coverage

Coverage

86.67%

Importance

Changes

0

17 Methods

Rating	Name	Duplication	Size	Complexity
A	__construct()	0	13	2
A	getQueryToken()	0	3	1
A	setContextPage()	0	3	1
A	setDefaultNamespaces()	0	12	3
A	getQueryDescription()	0	19	3
A	getErrors()	0	3	1
A	getErrorString()	0	3	1
F	getSubqueryDescription()	0	100	25
B	getLinkDescription()	0	25	6
C	getClassDescription()	0	28	8
F	getPropertyDescription()	0	114	26
C	getArticleDescription()	0	49	9
C	finishLinkDescription()	0	42	11
C	readChunk()	0	32	11
A	pushDelimiter()	0	3	1
A	popDelimiter()	0	4	1
A	isPagePropertyType()	0	3	2

<?php

use SMW\DataTypeRegistry;
use SMW\DIWikiPage;
use SMW\Query\Language\ClassDescription;
use SMW\Query\Language\ConceptDescription;
use SMW\Query\Language\Description;
use SMW\Query\Language\NamespaceDescription;
use SMW\Query\Language\SomeProperty;
use SMW\Query\Language\ThingDescription;
use SMW\Query\Parser\DescriptionProcessor;
use SMW\Query\QueryToken;

/**
 * Objects of this class are in charge of parsing a query string in order
 * to create an SMWDescription. The class and methods are not static in order
 * to more cleanly store the intermediate state and progress of the parser.
 * @ingroup SMWQuery
 * @author Markus Krötzsch
 */
class SMWQueryParser {

PSR1 recommends that each class must be in a namespace of at least one level to avoid collisions.

	private $separatorStack; // list of open blocks ("parentheses") that need closing at current step
	private $currentString; // remaining string to be parsed (parsing eats query string from the front)

	private $defaultNamespace; // description of the default namespace restriction, or NULL if not used

	private $categoryPrefix; // cache label of category namespace . ':'
	private $conceptPrefix; // cache label of concept namespace . ':'
	private $categoryPrefixCannonical; // cache canonnical label of category namespace . ':'
	private $conceptPrefixCannonical; // cache canonnical label of concept namespace . ':'
	private $queryFeatures; // query features to be supported, format similar to $smwgQFeatures

	/**
	 * @var DescriptionProcessor
	 */
	private $descriptionProcessor;

	/**
	 * @var QueryToken
	 */
	private $queryToken;

	public function __construct( $queryFeatures = false ) {
		global $wgContLang, $smwgQFeatures;

Use of global functionality is not recommended; it makes your code harder to test, and less reusable.

		$this->categoryPrefix = $wgContLang->getNsText( NS_CATEGORY ) . ':';
		$this->conceptPrefix = $wgContLang->getNsText( SMW_NS_CONCEPT ) . ':';
		$this->categoryPrefixCannonical = 'Category:';
		$this->conceptPrefixCannonical = 'Concept:';

		$this->defaultNamespace = null;
		$this->queryFeatures = $queryFeatures === false ? $smwgQFeatures : $queryFeatures;
		$this->descriptionProcessor = new DescriptionProcessor( $this->queryFeatures );
		$this->queryToken = new QueryToken();
	}

	/**
	 * @since 2.5
	 *
	 * @return QueryToken
	 */
	public function getQueryToken() {
		return $this->queryToken;
	}

	/**
	 * @since 2.4
	 *
	 * @param DIWikiPage|null $contextPage
	 */
	public function setContextPage( DIWikiPage $contextPage = null ) {
		$this->descriptionProcessor->setContextPage( $contextPage );
	}

	/**
	 * Provide an array of namespace constants that are used as default restrictions.
	 * If NULL is given, no such default restrictions will be added (faster).
	 */
	public function setDefaultNamespaces( $namespaceArray ) {
		$this->defaultNamespace = null;

		if ( !is_null( $namespaceArray ) ) {
			foreach ( $namespaceArray as $ns ) {
				$this->defaultNamespace = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom(
					$this->defaultNamespace,
					new NamespaceDescription( $ns )
				);
			}
		}
	}

	/**
	 * Compute an SMWDescription from a query string. Returns whatever descriptions could be
	 * wrestled from the given string (the most general result being SMWThingDescription if
	 * no meaningful condition was extracted).
	 *
	 * @param string $queryString
	 *
	 * @return Description
	 */
	public function getQueryDescription( $queryString ) {

		$this->descriptionProcessor->clear();
		$this->currentString = $queryString;
		$this->separatorStack = array();
		$setNS = false;
		$result = $this->getSubqueryDescription( $setNS );

		if ( !$setNS ) { // add default namespaces if applicable
			$result = $this->descriptionProcessor->constructConjunctiveCompoundDescriptionFrom( $this->defaultNamespace, $result );
		}

		if ( is_null( $result ) ) { // parsing went wrong, no default namespaces
			$result = new ThingDescription();
		}


		return $result;
	}

	/**
	 * Return array of error messages (possibly empty).
	 *
	 * @return array
	 */
	public function getErrors() {
		return $this->descriptionProcessor->getErrors();
	}

	/**
	 * Return error message or empty string if no error occurred.
	 *
	 * @return string
	 */
	public function getErrorString() {
		return smwfEncodeMessages( $this->getErrors() );
	}

	/**
	 * Compute an SMWDescription for current part of a query, which should
	 * be a standalone query (the main query or a subquery enclosed within
	 * "\<q\>...\</q\>". Recursively calls similar methods and returns NULL upon error.
	 *
	 * The call-by-ref parameter $setNS is a boolean. Its input specifies whether
	 * the query should set the current default namespace if no namespace restrictions
	 * were given. If false, the calling super-query is happy to set the required
	 * NS-restrictions by itself if needed. Otherwise the subquery has to impose the defaults.
	 * This is so, since outermost queries and subqueries of disjunctions will have to set
	 * their own default restrictions.
	 *
	 * The return value of $setNS specifies whether or not the subquery has a namespace
	 * specification in place. This might happen automatically if the query string imposes
	 * such restrictions. The return value is important for those callers that otherwise
	 * set up their own restrictions.
	 *
	 * Note that $setNS is no means to switch on or off default namespaces in general,
	 * but just controls query generation. For general effect, the default namespaces
	 * should be set to NULL.
	 *
	 * @return Description|null
	 */
	private function getSubqueryDescription( &$setNS ) {
		$conjunction = null;      // used for the current inner conjunction
		$disjuncts = array();     // (disjunctive) array of subquery conjunctions
		$hasNamespaces = false;   // does the current $conjnuction have its own namespace restrictions?
		$mustSetNS = $setNS;      // must NS restrictions be set? (may become true even if $setNS is false)

		$continue = ( $chunk = $this->readChunk() ) !== ''; // skip empty subquery completely, thorwing an error

		while ( $continue ) {
			$setsubNS = false;

			switch ( $chunk ) {
				case '[[': // start new link block
					$ld = $this->getLinkDescription( $setsubNS );

					if ( !is_null( $ld ) ) {
						$conjunction = $this->descriptionProcessor->constructConjunctiveCompoundDescriptionFrom( $conjunction, $ld );
					}
				break;
				case 'AND':
				case '<q>': // enter new subquery, currently irrelevant but possible
					$this->pushDelimiter( '</q>' );
					$conjunction = $this->descriptionProcessor->constructConjunctiveCompoundDescriptionFrom( $conjunction, $this->getSubqueryDescription( $setsubNS ) );
				break;
				case 'OR':
				case '||':
				case '':
				case '</q>': // finish disjunction and maybe subquery
					if ( !is_null( $this->defaultNamespace ) ) { // possibly add namespace restrictions
						if ( $hasNamespaces && !$mustSetNS ) {
							// add NS restrictions to all earlier conjunctions (all of which did not have them yet)
							$mustSetNS = true; // enforce NS restrictions from now on
							$newdisjuncts = array();

							foreach ( $disjuncts as $conj ) {
								$newdisjuncts[] = $this->descriptionProcessor->constructConjunctiveCompoundDescriptionFrom( $conj, $this->defaultNamespace );
							}

							$disjuncts = $newdisjuncts;
						} elseif ( !$hasNamespaces && $mustSetNS ) {
							// add ns restriction to current result
							$conjunction = $this->descriptionProcessor->constructConjunctiveCompoundDescriptionFrom( $conjunction, $this->defaultNamespace );
						}
					}

					$disjuncts[] = $conjunction;
					// start anew
					$conjunction = null;
					$hasNamespaces = false;

					// finish subquery?
					if ( $chunk == '</q>' ) {
						if ( $this->popDelimiter( '</q>' ) ) {
							$continue = false; // leave the loop
						} else {
							$this->descriptionProcessor->addErrorWithMsgKey( 'smw_toomanyclosing', $chunk );
							return null;
						}
					} elseif ( $chunk === '' ) {
						$continue = false;
					}
				break;
				case '+': // "... AND true" (ignore)

50% of this comment could be valid code. Did you maybe forget this after debugging?

				break;
				default: // error: unexpected $chunk
					$this->descriptionProcessor->addErrorWithMsgKey( 'smw_unexpectedpart', $chunk );
					// return null; // Try to go on, it can only get better ...

50% of this comment could be valid code. Did you maybe forget this after debugging?

			}

			if ( $setsubNS ) { // namespace restrictions encountered in current conjunct
				$hasNamespaces = true;
			}

			if ( $continue ) { // read on only if $continue remained true
				$chunk = $this->readChunk();
			}
		}

		if ( count( $disjuncts ) > 0 ) { // make disjunctive result
			$result = null;

			foreach ( $disjuncts as $d ) {
				if ( is_null( $d ) ) {
					$this->descriptionProcessor->addErrorWithMsgKey( 'smw_emptysubquery' );
					$setNS = false;
					return null;
				} else {
					$result = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $result, $d );
				}
			}
		} else {
			$this->descriptionProcessor->addErrorWithMsgKey( 'smw_emptysubquery' );
			$setNS = false;
			return null;
		}

		$setNS = $mustSetNS; // NOTE: also false if namespaces were given but no default NS descs are available

		return $result;
	}

	/**
	 * Compute an SMWDescription for current part of a query, which should
	 * be the content of "[[ ... ]]". Returns NULL upon error.
	 *
	 * Parameters $setNS has the same use as in getSubqueryDescription().
	 */
	private function getLinkDescription( &$setNS ) {
		// This method is called when we encountered an opening '[['. The following
		// block could be a Category-statement, fixed object, or property statement.
		$chunk = $this->readChunk( '', true, false ); // NOTE: untrimmed, initial " " escapes prop. chains

		if ( in_array( smwfNormalTitleText( $chunk ),
			array( $this->categoryPrefix, $this->conceptPrefix, $this->categoryPrefixCannonical, $this->conceptPrefixCannonical ) ) ) {
			return $this->getClassDescription( $setNS, (
				smwfNormalTitleText( $chunk ) == $this->categoryPrefix || smwfNormalTitleText( $chunk ) == $this->categoryPrefixCannonical
			) );
		} else { // fixed subject, namespace restriction, property query, or subquery
			$sep = $this->readChunk( '', false ); // do not consume hit, "look ahead"

			if ( ( $sep == '::' ) || ( $sep == ':=' ) ) {
				if ( $chunk{0} != ':' ) { // property statement
					return $this->getPropertyDescription( $chunk, $setNS );
				} else { // escaped article description, read part after :: to get full contents
					$chunk .= $this->readChunk( '\[\[|\]\]|\|\||\|' );
					return $this->getArticleDescription( trim( $chunk ), $setNS );
				}
			} else { // Fixed article/namespace restriction. $sep should be ]] or ||
				return $this->getArticleDescription( trim( $chunk ), $setNS );
			}
		}
	}

	/**
	 * Parse a category description (the part of an inline query that
	 * is in between "[[Category:" and the closing "]]" and create a
	 * suitable description.
	 */
	private function getClassDescription( &$setNS, $category = true ) {
		// note: no subqueries allowed here, inline disjunction allowed, wildcards allowed
		$result = null;
		$continue = true;

		while ( $continue ) {
			$chunk = $this->readChunk();

			if ( $chunk == '+' ) {
				$description = new NamespaceDescription( $category ? NS_CATEGORY : SMW_NS_CONCEPT );
				$result = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $result, $description );
			} else { // assume category/concept title
				/// NOTE: we add m_c...prefix to prevent problems with, e.g., [[Category:Template:Test]]
				$title = Title::newFromText( ( $category ? $this->categoryPrefix : $this->conceptPrefix ) . $chunk );

				if ( !is_null( $title ) ) {
					$diWikiPage = new SMWDIWikiPage( $title->getDBkey(), $title->getNameSpace(), '' );
					$desc = $category ? new ClassDescription( $diWikiPage ) : new ConceptDescription( $diWikiPage );
					$result = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $result, $desc );
				}
			}

			$chunk = $this->readChunk();
			$continue = ( $chunk == '||' ) && $category; // disjunctions only for cateories
		}

		return $this->finishLinkDescription( $chunk, false, $result, $setNS );

The variable $chunk does not seem to be defined for all execution paths leading up to this point.

	}

	/**
	 * Parse a property description (the part of an inline query that
	 * is in between "[[Some property::" and the closing "]]" and create a
	 * suitable description. The "::" is the first chunk on the current
	 * string.
	 */
	private function getPropertyDescription( $propertyName, &$setNS ) {
		$this->readChunk(); // consume separator ":=" or "::"

		// first process property chain syntax (e.g. "property1.property2::value"), escaped by initial " ":
		$propertynames = ( $propertyName{0} == ' ' ) ? array( $propertyName ) : explode( '.', $propertyName );
		$properties = array();
		$typeid = '_wpg';
		$inverse = false;

		foreach ( $propertynames as $name ) {
			if ( !$this->isPagePropertyType( $typeid ) ) { // non-final property in chain was no wikipage: not allowed
				$this->descriptionProcessor->addErrorWithMsgKey( 'smw_valuesubquery', $name );
				return null; ///TODO: read some more chunks and try to finish [[ ]]
			}

			$property = SMWPropertyValue::makeUserProperty( $name );

			if ( !$property->isValid() ) { // illegal property identifier
				$this->descriptionProcessor->addError( $property->getErrors() );
				return null; ///TODO: read some more chunks and try to finish [[ ]]
			}

			$typeid = $property->getDataItem()->findPropertyTypeID();

It seems like you code against a specific sub-type and not the parent class SMWDataItem as the method findPropertyTypeID() does only exist in the following sub-classes of SMWDataItem: SMWDIProperty, SMW\DIProperty. Maybe you want to instanceof check for one of these explicitly?

			$inverse = $property->isInverse();

The method SMWPropertyValue::isInverse() has been deprecated with message: since 1.6

			$properties[] = $property;
		} ///NOTE: after iteration, $property and $typeid correspond to last value

		$innerdesc = null;
		$continue = true;

		while ( $continue ) {
			$chunk = $this->readChunk();

			switch ( $chunk ) {
				case '+': // wildcard, add namespaces for page-type properties
					if ( !is_null( $this->defaultNamespace ) && ( $this->isPagePropertyType( $typeid ) || $inverse ) ) {
						$innerdesc = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $innerdesc, $this->defaultNamespace );
					} else {
						$innerdesc = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $innerdesc, new ThingDescription() );
					}
					$chunk = $this->readChunk();
				break;
				case '<q>': // subquery, set default namespaces
					if ( $this->isPagePropertyType( $typeid ) || $inverse ) {
						$this->pushDelimiter( '</q>' );
						$setsubNS = true;
						$innerdesc = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $innerdesc, $this->getSubqueryDescription( $setsubNS ) );
					} else { // no subqueries allowed for non-pages
						$this->descriptionProcessor->addErrorWithMsgKey( 'smw_valuesubquery', end( $propertynames ) );
						$innerdesc = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $innerdesc, new ThingDescription() );
					}
					$chunk = $this->readChunk();
				break;
				default: // normal object value
					// read value(s), possibly with inner [[...]]

40% of this comment could be valid code. Did you maybe forget this after debugging?

					$open = 1;
					$value = $chunk;
					$continue2 = true;
					// read value with inner [[, ]], ||

39% of this comment could be valid code. Did you maybe forget this after debugging?

					while ( ( $open > 0 ) && ( $continue2 ) ) {
						$chunk = $this->readChunk( '\[\[|\]\]|\|\||\|' );
						switch ( $chunk ) {
							case '[[': // open new [[ ]]

50% of this comment could be valid code. Did you maybe forget this after debugging?

								$open++;
							break;
							case ']]': // close [[ ]]

50% of this comment could be valid code. Did you maybe forget this after debugging?

								$open--;
							break;
							case '|':
							case '||': // terminates only outermost [[ ]]
								if ( $open == 1 ) {
									$open = 0;
								}
							break;
							case '': ///TODO: report error; this is not good right now
								$continue2 = false;
							break;
						}
						if ( $open != 0 ) {
							$value .= $chunk;
						}
					} ///NOTE: at this point, we normally already read one more chunk behind the value
					$outerDesription = $this->descriptionProcessor->constructDescriptionForPropertyObjectValue(
						$property->getDataItem(),

The variable $property does not seem to be defined for all execution paths leading up to this point.

$property->getDataItem() of type object<SMWDataItem> is not a sub-type of object<SMW\DIProperty>. It seems like you assume a child class of the class SMWDataItem to be always present.

						$value
					);

					$this->queryToken->addFromDesciption( $outerDesription );
					$innerdesc = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom(
						$innerdesc,
						$outerDesription
					);

			}
			$continue = ( $chunk == '||' );
		}

		if ( is_null( $innerdesc ) ) { // make a wildcard search
			$innerdesc = ( !is_null( $this->defaultNamespace ) && $this->isPagePropertyType( $typeid ) ) ?
							$this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $innerdesc, $this->defaultNamespace ) :
							$this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $innerdesc, new ThingDescription() );
			$this->descriptionProcessor->addErrorWithMsgKey( 'smw_propvalueproblem', $property->getWikiValue() );
		}

		$properties = array_reverse( $properties );

		foreach ( $properties as $property ) {
			$innerdesc = new SomeProperty( $property->getDataItem(), $innerdesc );

It seems like $innerdesc can be null; however, __construct() does not accept null, maybe add an additional type check?

		}

		$result = $innerdesc;

		return $this->finishLinkDescription( $chunk, false, $result, $setNS );

The variable $chunk does not seem to be defined for all execution paths leading up to this point.

	}

	/**
	 * Parse an article description (the part of an inline query that
	 * is in between "[[" and the closing "]]" assuming it is not specifying
	 * a category or property) and create a suitable description.
	 * The first chunk behind the "[[" has already been read and is
	 * passed as a parameter.
	 */
	private function getArticleDescription( $firstChunk, &$setNS ) {
		$chunk = $firstChunk;
		$result = null;
		$continue = true;

		while ( $continue ) {
			if ( $chunk == '<q>' ) { // no subqueries of the form [[<q>...</q>]] (not needed)

				$this->descriptionProcessor->addErrorWithMsgKey( 'smw_misplacedsubquery' );
				return null;
			}

			$list = preg_split( '/:/', $chunk, 3 ); // ":Category:Foo" "User:bar"  ":baz" ":+"

50% of this comment could be valid code. Did you maybe forget this after debugging?

			if ( ( $list[0] === '' ) && ( count( $list ) == 3 ) ) {
				$list = array_slice( $list, 1 );
			}
			if ( ( count( $list ) == 2 ) && ( $list[1] == '+' ) ) { // try namespace restriction

				$idx = \SMW\Localizer::getInstance()->getNamespaceIndexByName( $list[0] );

				if ( $idx !== false ) {
					$result = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom( $result, new NamespaceDescription( $idx ) );

It seems like $idx defined by \SMW\Localizer::getInstance()->getNamespaceIndexByName($list[0]) on line 477 can also be of type boolean; however, SMW\Query\Language\NamespaceDescription::__construct() does only seem to accept integer, maybe add an additional type check?

				}
			} else {
				$outerDesription = $this->descriptionProcessor->constructDescriptionForWikiPageValueChunk(
					$chunk
				);

				$this->queryToken->addFromDesciption( $outerDesription );

				$result = $this->descriptionProcessor->constructDisjunctiveCompoundDescriptionFrom(
					$result,
					$outerDesription
				);
			}

			$chunk = $this->readChunk( '\[\[|\]\]|\|\||\|' );

			if ( $chunk == '||' ) {
				$chunk = $this->readChunk( '\[\[|\]\]|\|\||\|' );
				$continue = true;
			} else {
				$continue = false;
			}
		}

		return $this->finishLinkDescription( $chunk, true, $result, $setNS );
	}

	private function finishLinkDescription( $chunk, $hasNamespaces, $result, &$setNS ) {
		if ( is_null( $result ) ) { // no useful information or concrete error found
			$this->descriptionProcessor->addErrorWithMsgKey( 'smw_unexpectedpart', $chunk ); // was smw_badqueryatom
		} elseif ( !$hasNamespaces && $setNS && !is_null( $this->defaultNamespace  ) ) {
			$result = $this->descriptionProcessor->constructConjunctiveCompoundDescriptionFrom( $result, $this->defaultNamespace );
			$hasNamespaces = true;
		}

		$setNS = $hasNamespaces;

		if ( $chunk == '|' ) { // skip content after single |, but report a warning
			// Note: Using "|label" in query atoms used to be a way to set the mainlabel in SMW <1.0; no longer supported now
			$chunk = $this->readChunk( '\]\]' );
			$labelpart = '|';
			if ( $chunk != ']]' ) {
				$labelpart .= $chunk;
				$chunk = $this->readChunk( '\]\]' );
			}
			$this->descriptionProcessor->addErrorWithMsgKey( 'smw_unexpectedpart', $labelpart );
		}

		if ( $chunk != ']]' ) {
			// What happended? We found some chunk that could not be processed as
			// link content (as in [[Category:Test<q>]]), or the closing ]] are
			// just missing entirely.
			if ( $chunk !== '' ) {
				$this->descriptionProcessor->addErrorWithMsgKey( 'smw_misplacedsymbol', $chunk );

				// try to find a later closing ]] to finish this misshaped subpart
				$chunk = $this->readChunk( '\]\]' );

				if ( $chunk != ']]' ) {
					$chunk = $this->readChunk( '\]\]' );
				}
			}
			if ( $chunk === '' ) {
				$this->descriptionProcessor->addErrorWithMsgKey( 'smw_noclosingbrackets' );
			}
		}

		return $result;
	}

	/**
	 * Get the next unstructured string chunk from the query string.
	 * Chunks are delimited by any of the special strings used in inline queries
	 * (such as [[, ]], <q>, ...). If the string starts with such a delimiter,
	 * this delimiter is returned. Otherwise the first string in front of such a
	 * delimiter is returned.
	 * Trailing and initial spaces are ignored if $trim is true, and chunks
	 * consisting only of spaces are not returned.
	 * If there is no more qurey string left to process, the empty string is
	 * returned (and in no other case).
	 *
	 * The stoppattern can be used to customise the matching, especially in order to
	 * overread certain special symbols.
	 *
	 * $consume specifies whether the returned chunk should be removed from the
	 * query string.
	 */
	private function readChunk( $stoppattern = '', $consume = true, $trim = true ) {
		if ( $stoppattern === '' ) {
			$stoppattern = '\[\[|\]\]|::|:=|<q>|<\/q>' .
				'|^' . $this->categoryPrefix . '|^' . $this->categoryPrefixCannonical .
				'|^' . $this->conceptPrefix . '|^' . $this->conceptPrefixCannonical .
				'|\|\||\|';
		}
		$chunks = preg_split( '/[\s]*(' . $stoppattern . ')/iu', $this->currentString, 2, PREG_SPLIT_DELIM_CAPTURE );
		if ( count( $chunks ) == 1 ) { // no matches anymore, strip spaces and finish
			if ( $consume ) {
				$this->currentString = '';
			}

			return $trim ? trim( $chunks[0] ) : $chunks[0];
		} elseif ( count( $chunks ) == 3 ) { // this should generally happen if count is not 1
			if ( $chunks[0] === '' ) { // string started with delimiter
				if ( $consume ) {
					$this->currentString = $chunks[2];
				}

				return $trim ? trim( $chunks[1] ) : $chunks[1];
			} else {
				if ( $consume ) {
					$this->currentString = $chunks[1] . $chunks[2];
				}

				return $trim ? trim( $chunks[0] ) : $chunks[0];
			}
		} else {
			return false;
		} // should never happen
	}

	/**
	 * Enter a new subblock in the query, which must at some time be terminated by the
	 * given $endstring delimiter calling popDelimiter();
	 */
	private function pushDelimiter( $endstring ) {
		array_push( $this->separatorStack, $endstring );
	}

	/**
	 * Exit a subblock in the query ending with the given delimiter.
	 * If the delimiter does not match the top-most open block, false
	 * will be returned. Otherwise return true.
	 */
	private function popDelimiter( $endstring ) {
		$topdelim = array_pop( $this->separatorStack );
		return ( $topdelim == $endstring );
	}

	private function isPagePropertyType( $typeid ) {
		return $typeid == '_wpg' || DataTypeRegistry::getInstance()->isSubDataType( $typeid );
	}

}