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<?php namespace ProcessWire;

require_once(PROCESSWIRE_CORE_PATH . "Selector.php"); 

/**
 * ProcessWire Selectors
 *
 * #pw-summary Processes a selector string into a WireArray of Selector objects. 
 * #pw-summary-static-helpers Static helper methods useful in analyzing selector strings outside of this class. 
 * #pw-body = 
 * This Selectors class is used internally by ProcessWire to provide selector string (and array) matching throughout the core.
 * 
 * ~~~~~
 * $selectors = new Selectors("sale_price|retail_price>100, currency=USD|EUR");
 * if($selectors->matches($page)) {
 *   // selector string matches the given $page (which can be any Wire-derived item)
 * }
 * ~~~~~
 * ~~~~~
 * // iterate and display what's in this Selectors object
 * foreach($selectors as $selector) {
 *   echo "<p>";
 *   echo "Field(s): " . implode('|', $selector->fields) . "<br>"; 
 *   echo "Operator: " . $selector->operator . "<br>"; 
 *   echo "Value(s): " . implode('|', $selector->values) . "<br>";
 *   echo "</p>";
 * }
 * ~~~~~
 * #pw-body
 * 
 * @link https://processwire.com/api/selectors/ Official Selectors Documentation
 * @method Selector[] getIterator()
 * 
 * ProcessWire 3.x, Copyright 2021 by Ryan Cramer
 * https://processwire.com
 * 
 * @todo Move static helper methods to dedicated API var/class so this class can be more focused
 * @todo Determine whether Selector array handling methods would be better in separate/descending class
 *
 */

class Selectors extends WireArray {

    /**
     * Maximum length for a selector operator
     *
     */
    const maxOperatorLength = 10; 

    /**
     * Static array of Selector types of $operator => $className
     *
     */
    static $selectorTypes = array();

    /**
     * Array of all individual characters used by operators
     *
     */
    static $operatorChars = array();

    /**
     * Original saved selector string, used for debugging purposes
     *
     */
    protected $selectorStr = '';

    /**
     * Whether or not variables like [user.id] should be converted to actual value
     * 
     * In most cases this should be true. 
     * 
     * @var bool
     *
     */
    protected $parseVars = true;

    /**
     * API variable names that are allowed to be parsed
     * 
     * @var array
     * 
     */
    protected $allowedParseVars = array(
        'session', 
        'page', 
        'user',
    );

    /**
     * Types of quotes selector values may be surrounded in
     *
     */
    protected $quotes = array(
        // opening => closing
        '"' => '"',
        "'" => "'",
        '[' => ']',
        '{' => '}',
        '(' => ')',
    );
    
    /**
     * Given a selector string, extract it into one or more corresponding Selector objects, iterable in this object.
     * 
     * @param string|null|array $selector Selector string or array. If not provided here, please follow-up with a setSelectorString($str) call. 
     *
     */
    public function __construct($selector = null) {
        parent::__construct();
        if(!is_null($selector)) $this->init($selector);
    }

    /**
     * Set the selector string or array (if not set already from the constructor)
     * 
     * ~~~~~
     * $selectors = new Selectors();
     * $selectors->init("sale_price|retail_price>100, currency=USD|EUR");
     * ~~~~~
     * 
     * @param string|array $selector
     * 
     */
    public function init($selector) {
        if(is_array($selector)) {
            $this->setSelectorArray($selector);
        } else if(is_object($selector) && $selector instanceof Selector) {
            $this->add($selector);
        } else {
            $this->setSelectorString($selector);
        }
    }

    /**
     * Set the selector string 
     * 
     * #pw-internal
     * 
     * @param string $selectorStr
     * 
     */
    public function setSelectorString($selectorStr) {
        $this->selectorStr = $selectorStr;
        $this->extractString(trim($selectorStr)); 
    }
    
    /**
     * Import items into this WireArray.
     * 
     * #pw-internal
     * 
     * @throws WireException
     * @param string|WireArray $items Items to import.
     * @return WireArray This instance.
     *
     */
    public function import($items) {
        if(is_string($items)) {
            $this->extractString($items);   
            return $this;
        } else {
            return parent::import($items); 
        }
    }

    /**
     * Per WireArray interface, return true if the item is a Selector instance
     * 
     * #pw-internal
     * 
     * @param Selector $item
     * @return bool
     *
     */
    public function isValidItem($item) {
        return is_object($item) && $item instanceof Selector; 
    }

    /**
     * Per WireArray interface, return a blank Selector
     * 
     * #pw-internal
     *
     */
    public function makeBlankItem() {
        return $this->wire(new SelectorEqual('',''));
    }

    /**
     * Create a new Selector object from a field name, operator, and value
     * 
     * This is mostly for internal use, as the Selectors object already does this when you pass it
     * a selector string in the constructor or init() method. 
     * 
     * #pw-group-advanced
     *
     * @param string $field Field name or names (separated by a pipe)
     * @param string $operator Operator, i.e. "="
     * @param string|array $value Value or values (separated by a pipe)
     * @return Selector Returns the correct type of `Selector` object that corresponds to the given `$operator`.
     * @throws WireException
     *
     */
    public function create($field, $operator, $value) {
        $not = false;
        if(!isset(self::$selectorTypes[$operator])) {
            // unrecognized operator, see if it's an alternate placement for NOT "!" statement
            $op = ltrim("$operator", '!');
            if(isset(self::$selectorTypes[$op])) {
                $operator = $op;
                $not = true;
            } else {
                if(is_array($value)) $value = implode('|', $value);
                if(is_array($field)) $field = implode('|', $field);
                $debug = $this->wire('config')->debug ? "field='$field', value='$value', selector: '$this->selectorStr'" : "";
                if(empty($operator)) $operator = '[empty]';
                throw new WireException("Unknown Selector operator: '$operator' -- was your selector value properly escaped? $debug");
            }
        }
        $class = wireClassName(self::$selectorTypes[$operator], true); 
        $selector = $this->wire(new $class($field, $value)); 
        if($not) $selector->not = true;
        return $selector;       
    }

    /**
     * Given a selector string, populate to Selector objects in this Selectors instance
     *
     * @param string $str The string containing a selector (or multiple selectors, separated by commas)
     *
     */
    protected function extractString($str) {

        while(strlen($str)) {

            $not = false;
            $quote = '';    
            if(strpos($str, '!') === 0) {
                $str = ltrim($str, '!');
                $not = true; 
            }
            $group = $this->extractGroup($str);     
            $field = $this->extractField($str); 
            $operators = $this->extractOperators($str);
            $operator = array_shift($operators);
            $value = $this->extractValue($str, $quote); 

            if($this->parseVars && $quote === '[' && $this->valueHasVar($value)) {
                // parse an API variable property to a string value
                $v = $this->parseValue($value); 
                if($v !== null) {
                    $value = $v;
                    $quote = '';
                }
            }

            if($field || $value || strlen("$value")) {
                $selector = $this->create($field, $operator, $value);
                if(!is_null($group)) $selector->group = $group; 
                if($quote) $selector->quote = $quote; 
                if($not) $selector->not = true; 
                if(count($operators)) $selector->altOperators = $operators;
                $this->add($selector); 
            }
        }

    }
    
    /**
     * Given a string like name@field=... or @field=... extract the part that comes before the @
     *
     * This part indicates the group name, which may also be blank to indicate grouping with other blank grouped items
     *
     * @param string $str
     * @return null|string
     *
     */
    protected function extractGroup(&$str) {
        $group = null;
        $pos = strpos($str, '@'); 
        if($pos === false) return $group; 
        if($pos === 0) {
            $group = '';
            $str = substr($str, 1); 
        } else if(preg_match('/^([-_a-zA-Z0-9]*)@(.*)/', $str, $matches)) {
            $group = $matches[1]; 
            $str = $matches[2];
        }
        return $group; 
    }

    /**
     * Given a string starting with a field, return that field, and remove it from $str. 
     * 
     * @param string $str
     * @return string
     *
     */
    protected function extractField(&$str) {
        $field = '';
        
        if(strpos($str, '(') === 0) {
            // OR selector where specification of field name is optional and = operator is assumed
            $str = '=(' . substr($str, 1); 
            return $field; 
        }

        if(preg_match('/^(!?[_|.a-zA-Z0-9]+)(.*)/', $str, $matches)) {

            $field = trim($matches[1], '|'); 
            $str = $matches[2];

            if(strpos($field, '|')) {
                $field = explode('|', $field); 
            }

        }
        return $field; 
    }


    /**
     * Given a string starting with an operator, return that operator, and remove it from $str. 
     * 
     * @param string $str
     * @param array $operatorChars
     * @return string
     * @deprecated Replaced by extractOperators()
     * @todo this method can be removed once confirmed nothing else uses it
     *
     */
    protected function extractOperator(&$str, array $operatorChars) {
        $n = 0;
        $operator = '';
        $lastOperator = '';
        while(isset($str[$n]) && in_array($str[$n], $operatorChars) && $n < self::maxOperatorLength) {
            $operator .= $str[$n]; 
            if(self::isOperator($operator)) {
                $lastOperator = $operator;
            } else if($lastOperator) {
                $operator = $lastOperator;
                break;
            }
            $n++; 
        }
        if($operator) $str = substr($str, $n); 
        return $operator; 
    }
    
    /**
     * Given a string starting with an operator, return that operator, and remove it from $str.
     *
     * @param string $str
     * @return array
     *
     */
    protected function extractOperators(&$str) {
        
        $n = 0;
        $not = false;
        $operator = '';
        $lastOperator = '';
        $operators = array();
        $operatorChars = self::getOperatorChars();
    
        while(isset($str[$n]) && isset($operatorChars[$str[$n]])) {
            $c = $str[$n];
            if($operator === '!' && $c !== '=') {
                // beginning of operator negation that’s not "!="
                $not = true;
                $operator = ltrim($operator, '!');
            }
            $operator .= $c;
            if(self::isOperator($operator)) {
                $lastOperator = $operator;
            } else if($lastOperator) {
                if($not) $lastOperator = "!$lastOperator";
                $operators[$lastOperator] = $lastOperator;
                $lastOperator = '';
                $operator = $c;
                $not = false;
            }
            $n++; 
        }
        
        if($lastOperator) {
            if($not) $lastOperator = "!$lastOperator";
            $operators[$lastOperator] = $lastOperator;
        }
        
        if(count($operators)) {
            $str = substr($str, $n);
        }
        
        if($operator && !isset($operators[$lastOperator])) {
            // leftover characters in $operator, maybe from operator in wrong order
            $fail = true;
            if(!count($operators)) {
                // check if operator has a typo we can fix
                // isOperator with 2nd argument true allows for and corrects some order mixups
                $op = self::isOperator($operator, true);
                if($op) {
                    if($not) $op = "!$op";
                    $operators[$op] = $op;
                    $str = substr($str, $n);
                    $fail = false;
                }
            }
            if($fail) {
                throw new WireException("Unrecognized operator: $operator"); 
            }
        }
        
        return $operators;
    }

    /**
     * Early-exit optimizations for extractValue
     * 
     * @param string $str String to extract value from, $str will be modified if extraction successful
     * @param string $openingQuote Opening quote character, if string has them, blank string otherwise
     * @param string $closingQuote Closing quote character, if string has them, blank string otherwise
     * @return mixed Returns found value if successful, boolean false if not
     *
     */
    protected function extractValueQuick(&$str, $openingQuote, $closingQuote) {
        
        // determine where value ends
        $offset = 0;
        if($openingQuote) $offset++; // skip over leading quote
        $commaPos = strpos("$str,", $closingQuote . ',', $offset); // "$str," just in case value is last and no trailing comma
        
        if($commaPos === false && $closingQuote) {
            // if closing quote and comma didn't match, try to match just comma in case of "something"<space>,
            $str1 = substr($str, 1);
            $commaPos = strpos($str1, ',');
            if($commaPos !== false) {
                $closingQuotePos = strpos($str1, $closingQuote); 
                if($closingQuotePos > $commaPos) {
                    // comma is in quotes and thus not one we want to work with
                    return false;
                } else {
                    // increment by 1 since it was derived from a string at position 1 (rather than 0)
                    $commaPos++;
                }
            }
        }

        if($commaPos === false) {
            // value is the last one in $str
            $commaPos = strlen($str); 
            
        } else if($commaPos && $str[$commaPos-1] === '//') {
            // escaped comma or closing quote means no optimization possible here
            return false; 
        }
        
        // extract the value for testing
        $value = substr($str, 0, $commaPos);
    
        // if there is an operator present, it might be a subselector or OR-group
        if(self::stringHasOperator($value)) return false;
    
        if($openingQuote) {
            // if there were quotes, trim them out
            $value = trim($value, $openingQuote . $closingQuote); 
        }

        // determine if there are any embedded quotes in the value
        $hasEmbeddedQuotes = false; 
        foreach($this->quotes as $open => $close) {
            if(strpos($value, $open)) $hasEmbeddedQuotes = true; 
        }
        
        // if value contains quotes anywhere inside of it, abort optimization
        if($hasEmbeddedQuotes) return false;
    
        // does the value contain possible OR conditions?
        if(strpos($value, '|') !== false) {
            
            // if there is an escaped pipe, abort optimization attempt
            if(strpos($value, '\\' . '|') !== false) return false; 
        
            // if value was surrounded in "quotes" or 'quotes' abort optimization attempt
            // as the pipe is a literal value rather than an OR
            if($openingQuote == '"' || $openingQuote == "'") return false;
        
            // we have valid OR conditions, so convert to an array
            $value = explode('|', $value); 
        }

        // if we reach this point we have a successful extraction and can remove value from str
        // $str = $commaPos ? trim(substr($str, $commaPos+1)) : '';
        $str = trim(substr($str, $commaPos+1));

        // successful optimization
        return $value; 
    }

    /**
     * Given a string starting with a value, return that value, and remove it from $str. 
     *
     * @param string $str String to extract value from
     * @param string $quote Automatically populated with quote type, if found
     * @return array|string Found values or value (excluding quotes)
     *
     */
    protected function extractValue(&$str, &$quote) {

        $str = trim($str); 
        if(!strlen($str)) return '';
        
        if(isset($this->quotes[$str[0]])) {
            $openingQuote = $str[0]; 
            $closingQuote = $this->quotes[$openingQuote];
            $quote = $openingQuote; 
            $n = 1; 
        } else {
            $openingQuote = '';
            $closingQuote = '';
            $n = 0; 
        }
        
        $value = $this->extractValueQuick($str, $openingQuote, $closingQuote); // see if we can do a quick exit
        if($value !== false) return $value; 

        $value = '';
        $lastc = '';
        $quoteDepth = 0;
        $inDoubleQuote = false; // applies only if openingQuote is populated and not itself a double quote

        do {
            if(!isset($str[$n])) break;

            $c = $str[$n]; 

            if($openingQuote) {
                // we are in a quoted value string

                if($c === $closingQuote && !$inDoubleQuote) { 
                    // closing quote for previously opened quote
                    
                    if($lastc !== '\\') {
                        // same quote that opened, and not escaped or double quoted
                        // means the end of the value
                        
                        if($quoteDepth > 0) {
                            // closing of an embedded quote
                            $quoteDepth--;
                        } else {
                            $n++; // skip over quote 
                            $quote = $openingQuote;
                            break;
                        }

                    } else {
                        // this is an intentionally escaped quote, remove the escape
                        $value = rtrim($value, '\\'); 
                    }
                    
                } else if($c === $openingQuote && $openingQuote !== $closingQuote) {
                    // another opening quote of the same type encountered while already in a quote
                    if(!$inDoubleQuote) $quoteDepth++;
                    
                } else if($c === '"') {
                    // double quote char 
                    // not reachable if openingQuote was a double quote
                    if($inDoubleQuote) {
                        // closing a previously opened double quote
                        $inDoubleQuote = false;
                    } else {
                        // potentially applicable double quote
                        list($on, $op) = array($n, '', '');
                        // check if an operator came before the quote
                        while($on > 0 && isset(self::$operatorChars[$str[--$on]])) {
                            $op = self::$operatorChars[$str[$on]] . $op;
                        }
                        // if something valid does prefix the operator, cancel the operator
                        if(!$on || !$this->wire('sanitizer')->fieldName($str[$on])) $op = '';
                        // if an operator came before the quote, and it closes somewhere,
                        // we will allow the embedded double quote
                        if(strlen($op) && self::isOperator($op) && strrpos($str, '"') > $n) {
                            // opening a double quote after an operator
                            $inDoubleQuote = true;
                        } else {
                            // abandon the double quote
                            $c = null;
                        }
                    }
                }

            } else {
                // we are in an un-quoted value string

                if($c == ',' || $c == '|') {
                    if($lastc != '\\') {
                        // a non-quoted, non-escaped comma terminates the value
                        break;

                    } else {
                        // an intentionally escaped comma
                        // so remove the escape
                        $value = rtrim($value, '\\'); 
                    }
                }
            }

            if($c !== null) {
                $value .= $c;
                $lastc = $c;
            }

        } while(++$n);
        
        if($inDoubleQuote) $value .= '"'; // close double quote
        
        $len = strlen("$value");
        if($len) {
            $str = substr($str, $n);
            // if($len > self::maxValueLength) $value = substr($value, 0, self::maxValueLength);
        }

        $str = ltrim($str, ' ,"\']})'); // should be executed even if blank value

        // check if a pipe character is present next, indicating an OR value may be provided
        if(strlen($str) > 1 && substr($str, 0, 1) == '|') {
            $str = substr($str, 1); 
            // perform a recursive extract to account for all OR values
            $v = $this->extractValue($str, $quote); 
            $quote = ''; // we don't support separately quoted OR values
            $value = array($value); 
            if(is_array($v)) $value = array_merge($value, $v); 
                else $value[] = $v; 
        }

        return $value; 
    }

    /**
     * Given a value string with an "api_var" or "api_var.property" return the string value of the property
     * 
     * #pw-internal
     *
     * @param string $value var or var.property
     * @return null|string Returns null if it doesn't resolve to anything or a string of the value it resolves to
     *
     */
    public function parseValue($value) {
        if(!preg_match('/^\$?[_a-zA-Z0-9]+(?:\.[_a-zA-Z0-9]+)?$/', $value)) return null;
        $property = '';
        if(strpos($value, '.')) list($value, $property) = explode('.', $value); 
        if(!in_array($value, $this->allowedParseVars)) return null; 
        $value = $this->wire($value); 
        if(is_null($value)) return null; // does not resolve to API var
        if(empty($property)) return (string) $value;  // no property requested, just return string value 
        if(!is_object($value)) return null; // property requested, but value is not an object
        return (string) $value->$property; 
    }
    
    /**
     * Set whether or not vars should be parsed
     *
     * By default this is true, so only need to call this method to disable variable parsing.
     * 
     * #pw-internal
     *
     * @param bool $parseVars
     *
     */
    public function setParseVars($parseVars) {
        $this->parseVars = $parseVars ? true : false;
    }

    /**
     * Does the given Selector value contain a parseable value?
     * 
     * #pw-internal
     * 
     * @param Selector $selector
     * @return bool
     * 
     */
    public function selectorHasVar(Selector $selector) {
        if($selector->quote != '[') return false; 
        $has = false;
        foreach($selector->values as $value) {
            if($this->valueHasVar($value)) {
                $has = true; 
                break;
            }
        }
        return $has;
    }

    /**
     * Does the given value contain an API var reference?
     * 
     * It is assumed the value was quoted in "[value]", and the quotes are not there now. 
     * 
     * #pw-internal
     *
     * @param string $value The value to evaluate
     * @return bool
     *
     */
    public function valueHasVar($value) {
        if(self::stringHasOperator($value)) return false;
        if(strpos($value, '.') !== false) {
            list($name, $subname) = explode('.', $value);
        } else {
            $name = $value;
            $subname = '';
        }
        if(!in_array($name, $this->allowedParseVars)) return false;
        if(strlen($subname) && $this->wire('sanitizer')->fieldName($subname) !== $subname) return false;
        return true; 
    }

    /**
     * Return array of all field names referenced in all of the Selector objects here
     * 
     * @param bool $subfields Default is to allow "field.subfield" fields, or specify false to convert them to just "field".
     * @return array Returned array has both keys and values as field names (same)
     * 
     */
    public function getAllFields($subfields = true) {
        $fields = array();
        foreach($this as $selector) {
            $field = $selector->field;
            if(!is_array($field)) $field = array($field);
            foreach($field as $f) {
                if(!$subfields && strpos($f, '.')) {
                    list($f, $subfield) = explode('.', $f, 2);
                    if($subfield) {} // ignore
                }
                $fields[$f] = $f;
            }
        }
        return $fields;
    }

    /**
     * Return array of all values referenced in all Selector objects here
     * 
     * @return array Returned array has both keys and values as field values (same)
     * 
     */
    public function getAllValues() {
        $values = array();
        foreach($this as $selector) {
            $value = $selector->value;
            if(!is_array($value)) $value = array($value);
            foreach($value as $v) {
                $values[$v] = $v;
            }
        }
        return $values;
    }

    /**
     * Does the given Wire match these Selectors?
     * 
     * @param Wire $item
     * @return bool
     * 
     */
    public function matches(Wire $item) {
        
        // if item provides it's own matches function, then let it have control
        if($item instanceof WireMatchable) return $item->matches($this);
    
        $matches = true;
        foreach($this as $selector) {
            $value = array();
            foreach($selector->fields as $property) {
                if(strpos($property, '.') && $item instanceof WireData) {
                    $value[] =  $item->getDot($property);
                } else {
                    $value[] = (string) $item->$property;
                }
            }
            if(!$selector->matches($value)) {
                $matches = false;
                // attempt any alternate operators, if present
                foreach($selector->altOperators as $altOperator) {
                    $altSelector = self::getSelectorByOperator($altOperator); 
                    if(!$altSelector) continue;
                    $this->wire($altSelector);
                    $selector->copyTo($altSelector);
                    $matches = $altSelector->matches($value);
                    if($matches) break;
                }
                // if neither selector nor altSelectors match then stop
                if(!$matches) break;
            }
        }
        
        return $matches;
    }

    /**
     * Return string indicating given data type for use in selector arrays
     * 
     * @param int|string|array $data
     * @return string
     * 
     */
    protected function getSelectorArrayType($data) {
        $dataType = '';
        if(is_int($data)) {
            $dataType = 'int';
        } else if(is_string($data)) {
            $dataType = 'string';
        } else if(is_array($data)) {
            $dataType = ctype_digit(implode('', array_keys($data))) ? 'array' : 'assoc';
            if($dataType == 'assoc' && isset($data['field'])) $dataType = 'verbose';
        } 
        return $dataType;   
    }

    /**
     * Extract and return operator from end of field name, as used by selector arrays
     * 
     * @param string $field
     * @return array
     * 
     */
    protected function getOperatorsFromField(&$field) {
        
        $operators = array_keys(self::$selectorTypes);
        $operatorsStr = implode('', $operators);
        $c = substr($field, -1);
        if(ctype_alnum($c)) return array('=');

        $op = '';
        while(strpos($operatorsStr, $c) !== false && strlen($field)) {
            $op = $c . $op;
            $field = substr($field, 0, -1);
            $c = substr($field, -1); 
        }
        
        if(empty($op)) return array('='); 
        
        $operators = $this->extractOperators($op);
        
        return $operators;
    }

    /**
     * Create this Selectors object from an array
     * 
     * #pw-internal
     *
     * @param array $a
     * @throws WireException
     *
     */
    public function setSelectorArray(array $a) {
        
        $groupCnt = 0;
        
        // fields that may only appear once in a selector
        $singles = array(
            'start' => '',
            'limit' => '',
            'end' => '',
        );
        
        foreach($a as $key => $data) {
            
            $keyType = $this->getSelectorArrayType($key);
            $dataType = $this->getSelectorArrayType($data);
            
            if($keyType == 'int' && $dataType == 'assoc') {
                // OR-group
                $groupCnt++;
                
                foreach($data as $k => $v) {
                    $s = $this->makeSelectorArrayItem($k, $v);
                    $selector1 = $this->create($s['field'], $s['operator'], $s['value']);
                    if(!empty($s['altOperators'])) $selector1->altOperators = $s['altOperators'];
                    $selector2 = $this->create("or$groupCnt", "=", $selector1);
                    $selector2->quote = '(';
                    $this->add($selector2);
                }
                
            } else {
                
                $s = $this->makeSelectorArrayItem($key, $data, $dataType);
                $field = $s['field'];
                
                if(!is_array($field) && isset($singles[$field])) {
                    if(empty($singles[$field])) {
                        // mark it as present
                        $singles[$field] = true;
                    } else {
                        // skip, because this 'single' field has already appeared
                        continue;
                    }
                }
                
                $selector = $this->create($field, $s['operator'], $s['value']);
                
                if($s['not']) $selector->not = true;
                if($s['group']) $selector->group = $s['group'];
                if($s['quote']) $selector->quote = $s['quote'];
                if(!empty($s['altOperators'])) $selector->altOperators = $s['altOperators'];
                
                $this->add($selector);
            }
        }
    }

    /**
     * Return an array of an individual Selector info, for use by setSelectorArray() method
     * 
     * @param string|int $key
     * @param array $data
     * @param string $dataType One of 'string', 'array', 'assoc', or 'verbose'
     * @return array
     * @throws WireException
     * 
     */
    protected function makeSelectorArrayItem($key, $data, $dataType = '') {
        
        $sanitizer = $this->wire('sanitizer');
        $sanitize = 'selectorValue';
        $fields = array();
        $values = array();
        $operators = array('=');
        $whitelist = null;
        $not = false;
        $group = '';
        $find = ''; // sub-selector
        $quote = '';
        
        if(empty($dataType)) $dataType = $this->getSelectorArrayType($data);

        if(is_int($key) && $dataType == 'verbose') {

            // Verbose selector with associative array of properties, in this expected format: 
            // 
            // $data = array(
            //  'field' => array|string, // field name, or field names
            //  'value' => array|string|number|object, // value or values, or omit if using 'find' 
            //  ---the following are optional---
            //  'operator' => '=>', // operator, '=' is the default
            //  'not' => false, // specify true to make this a NOT condition (default=false)
            //  'sanitize' => 'selectorValue', // sanitizer method to use on value(s), 'selectorValue' is default
            //  'find' => array(...), // sub-selector to use instead of 'value'
            //  'whitelist' => null|array, // whitelist of allowed values, NULL is default, which means ignore. 
            //  );

            if(isset($data['fields']) && !isset($data['field'])) $data['field'] = $data['fields']; // allow plural alternate
            if(!isset($data['field'])) {
                throw new WireException("Invalid selectors array, lacks 'field' property for index $key");
            }

            if(isset($data['values']) && !isset($data['value'])) $data['value'] = $data['values']; // allow plural alternate
            if(!isset($data['value']) && !isset($data['find'])) {
                throw new WireException("Invalid selectors array, lacks 'value' property for index $key");
            }

            if(isset($data['sanitizer']) && !isset($data['sanitize'])) $data['sanitize'] = $data['sanitizer']; // allow alternate
            if(isset($data['sanitize'])) $sanitize = $sanitizer->fieldName($data['sanitize']);

            if(!empty($data['operator'])) $operators = $this->extractOperators($data['operator']);
            if(!empty($data['not'])) $not = (bool) $data['not'];

            // may use either 'group' or 'or' to specify or-group
            if(!empty($data['group'])) {
                $group = $sanitizer->fieldName($data['group']);
            } else if(!empty($data['or'])) {
                $group = $sanitizer->fieldName($data['or']);
            }

            if(!empty($data['find'])) {
                if(isset($data['value'])) throw new WireException("You may not specify both 'value' and 'find' at the same time");
                // if(!is_array($data['find'])) throw new WireException("Selector 'find' property must be specified as array"); 
                $find = $data['find'];
                $data['value'] = array();
            }

            if(isset($data['whitelist']) && $data['whitelist'] !== null) {
                $whitelist = $data['whitelist'];
                if(is_object($whitelist) && $whitelist instanceof WireArray) $whitelist = explode('|', (string) $whitelist);
                if(!is_array($whitelist)) $whitelist = array($whitelist);
            }

            if($sanitize && $sanitize != 'selectorValue' && !method_exists($sanitizer, $sanitize)) {
                throw new WireException("Unrecognized sanitize method: " . $sanitizer->name($sanitize));
            }

            $_fields = is_array($data['field']) ? $data['field'] : array($data['field']);
            $_values = is_array($data['value']) ? $data['value'] : array($data['value']);
            
        } else if(is_string($key)) {
            
            // Non-verbose selector, where $key is the field name and $data is the value
            // The $key field name may have an optional operator appended to it
        
            $operators = $this->getOperatorsFromField($key);
            $_fields = strpos($key, '|') ? explode('|', $key) : array($key);
            $_values = is_array($data) ? $data : array($data);
            
        } else if($dataType == 'array') {
            
            // selector in format: array('field', 'operator', 'value', 'sanitizer_method')
            // or array('field', 'operator', 'value', array('whitelist value1', 'whitelist value2', 'etc'))
            // or array('field', 'operator', 'value')
            // or array('field', 'value') where '=' is assumed operator
            $field = '';
            $value = array();
            
            if(count($data) == 4) {
                list($field, $operator, $value, $_sanitize) = $data;
                $operators = $this->extractOperators($operator); 
                if(is_array($_sanitize)) {
                    $whitelist = $_sanitize;
                } else {
                    $sanitize = $sanitizer->name($_sanitize);
                }

            } else if(count($data) == 3) {
                list($field, $operator, $value) = $data;
                $operators = $this->extractOperators($operator);
                
            } else if(count($data) == 2) {
                list($field, $value) = $data;
                $operators = $this->getOperatorsFromField($field);
            }
        
            if(is_array($field)) {
                $_fields = $field;
            } else {
                $_fields = strpos($field, '|') ? explode('|', $field) : array($field);
            }
            
            $_values = is_array($value) ? $value : array($value);
            
        } else {
            throw new WireException("Unable to resolve selector array");    
        }
    
        // make sure operator is valid
        foreach($operators as $operator) {
            if(!isset(self::$selectorTypes[$operator])) {
                throw new WireException("Unrecognized selector operator '$operator'");
            }
        }
    
        // determine field(s)
        foreach($_fields as $name) {
            if(strpos($name, '.') !== false) {
                // field name with multiple.named.parts, sanitize them separately
                $parts = explode('.', $name);
                foreach($parts as $n => $part) {
                    $parts[$n] = $sanitizer->fieldName($part);
                }
                $_name = implode('.', $parts);
            } else {
                $_name = $sanitizer->fieldName($name);
            }
            if($_name !== $name) {
                throw new WireException("Invalid Selectors field name (sanitized value '$_name' did not match specified value)");
            }
            $fields[] = $_name;
        }

        // convert WireArray types to an array of $_values
        if(count($_values) === 1) {
            $value = reset($_values);
            if(is_object($value) && $value instanceof WireArray) {
                $_values = explode('|', (string) $value);
            }
        }

        // determine value(s)
        foreach($_values as $value) {
            $_sanitize = $sanitize;
            if(is_array($value)) $value = 'array'; // we don't allow arrays here
            if(is_object($value)) $value = (string) $value;
            if(is_int($value) || (ctype_digit("$value") && strpos($value, '0') !== 0)) {
                $value = (int) $value;
                if($_sanitize == 'selectorValue') $_sanitize = ''; // no need to sanitize integer to string
            }
            if(is_array($whitelist) && !in_array($value, $whitelist)) {
                $fieldsStr = implode('|', $fields);
                throw new WireException("Value given for '$fieldsStr' is not in provided whitelist");
            }
            if($_sanitize === 'selectorValue') {
                $value = $sanitizer->selectorValue($value, array('useQuotes' => false)); 
            } else if($_sanitize) {
                $value = $sanitizer->$_sanitize($value);
            }
            $values[] = $value;
        }

        if($find) {
            // sub-selector find
            $quote = '[';
            $values = new Selectors($find);
            
        } else if($group) {
            // groups use quotes '()'
            $quote = '(';
        }
        
        return array(
            'field' => count($fields) > 1 ? $fields : reset($fields), 
            'value' => count($values) > 1 ? $values : reset($values), 
            'operator' => array_shift($operators), 
            'altOperators' => $operators,
            'not' => $not,
            'group' => $group,
            'quote' => $quote, 
        );
    }

    /**
     * Get the first selector that uses given field name
     * 
     * This is useful for quickly retrieving values of reserved properties like "include", "limit", "start", etc. 
     * 
     * Using **$or:** By default this excludes selectors that have fields in an OR expression, like "a|b|c". 
     * So if you specified field "a" it would not be matched. If you wanted it to still match, specify true 
     * for the $or argument.
     * 
     * Using **$all:** By default only the first matching selector is returned. If you want it to return all 
     * matching selectors in an array, then specify true for the $all argument. This changes the return value
     * to always be an array of Selector objects, or a blank array if no match. 
     * 
     * @param string $fieldName Name of field to return value for (i.e. "include", "limit", etc.)
     * @param bool $or Allow fields that appear in OR expressions? (default=false)
     * @param bool $all Return an array of all matching Selector objects? (default=false)
     * @return Selector|array|null Returns null if field not present in selectors (or blank array if $all mode)
     * 
     */
    public function getSelectorByField($fieldName, $or = false, $all = false) {
        
        $selector = null;
        $matches = array();
        
        foreach($this as $sel) {
            if($or) {
                if(!in_array($fieldName, $sel->fields)) continue;
            } else {
                if($sel->field() !== $fieldName) continue;
            }
            if($all) {
                $matches[] = $sel;
            } else {
                $selector = $sel;
                break;
            }
        }
        
        return $all ? $matches : $selector;
    }

    /**
     * Get the first selector that uses given field name AND has the given value
     *
     * Using **$or:** By default this excludes selectors that have fields or values in an OR expression, like "a|b|c".
     * So if you specified field "a" it would not be matched. If you wanted it to still match, specify true
     * for the $or argument.
     *
     * Using **$all:** By default only the first matching selector is returned. If you want it to return all
     * matching selectors in an array, then specify true for the $all argument. This changes the return value
     * to always be an array of Selector objects, or a blank array if no match.
     *
     * @param string $fieldName Name of field to match
     * @param string|int $value Value that must match
     * @param bool $or Allow fields and values that appear in OR expressions? (default=false)
     * @param bool $all Return an array of all matching Selector objects? (default=false)
     * @return Selector|array|null Returns null if field not present in selectors (or blank array if $all mode)
     * @since 3.0.142
     *
     */
    public function getSelectorByFieldValue($fieldName, $value, $or = false, $all = false) {
        
        $selectors = $this->getSelectorByField($fieldName, $or, true); 
        $matches = array();
        
        foreach($selectors as $sel) {
            /** @var Selector $sel */
            if($or) {
                if(in_array($value, $sel->values())) $matches[] = $sel;
            } else {
                if($sel->value() == $value) $matches[] = $sel;
            }
            if(!$all && count($matches)) break;
        }
        
        if($all) return $matches;
        
        return count($matches) ? $matches[0] : null;
    }

    /**
     * Value when typecast as string
     * 
     * @return string
     * 
     */
    public function __toString() {
        $str = '';
        foreach($this as $selector) {
            $str .= $selector->str . ", ";
        }
        return rtrim($str, ", ");
    }

    /**
     * Debug info
     * 
     * @return array
     * 
     */
    public function __debugInfo() {
        $info = parent::__debugInfo();
        $info['string'] = $this->__toString();
        return $info;
    }

    /**
     * Debug info for Selector item
     * 
     * @param Selector|mixed $item
     * @return array|mixed|null|string
     * 
     */
    public function debugInfoItem($item) {
        if($item instanceof Selector) return $item->__debugInfo();
        return parent::debugInfoItem($item);
    }

    /*** STATIC HELPERS *******************************************************************************/
    
    /**
     * Add a Selector type that processes a specific operator
     *
     * Static since there may be multiple instances of this Selectors class at runtime.
     * See Selector.php
     *
     * #pw-internal
     *
     * @param string $operator
     * @param string $class
     *
     */
    static public function addType($operator, $class) {
        self::$selectorTypes[$operator] = $class;
        for($n = 0; $n < strlen($operator); $n++) {
            $c = $operator[$n];
            self::$operatorChars[$c] = $c;
        }
    }

    /**
     * Get all operators allowed by selectors
     *
     * #pw-group-static-helpers
     *
     * @param array $options
     *  - `operator` (string): Return info for only this operator. When specified, only value is returned (default='').
     *  - `compareType` (int): Return only operators matching given `Selector::compareType*` constant (default=0).
     *  - `getIndexType` (string): Index type to use in returned array: 'operator', 'className', 'class', or 'none' (default='class')
     *  - `getValueType` (string): Value type to use in returned array: 'operator', 'class', 'className', 'label', 'description', 'compareType', 'verbose' (default='operator').
     *     If 'verbose' option used then assoc array returned for each operator containing 'class', 'className', 'operator', 'compareType', 'label', 'description'.
     * @return array|string|int Returned array where both keys and values are operators (or values are requested 'valueType' option)
     *   If 'operator' option specified, return value is string, int or array (requested 'valueType'), and there is no indexType.
     * @since 3.0.154
     *
     */
    static public function getOperators(array $options = array()) {

        $defaults = array(
            'operator' => '',
            'getIndexType' => 'class',
            'getValueType' => 'operator',
            'compareType' => 0,
        );

        $options = array_merge($defaults, $options);
        $operators = array();
        $compareType = (int) $options['compareType'];
        $indexType = $options['getIndexType'];
        $valueType = $options['getValueType'];
        $selectorTypes = self::$selectorTypes;

        if(!empty($options['operator'])) {
            $operator = $options['operator'];
            if($operator[0] === '!' && $operator !== '!=') {
                // negated operator
                $operator = ltrim($operator, '!');
            }
            if(!isset($selectorTypes[$operator])) {
                // operator does not exist
                if($valueType === 'compareType') return 0;
                return $valueType === 'verbose' ? array() : '';
            }
            $selectorTypes = array($operator => $selectorTypes[$operator]);
        }

        foreach($selectorTypes as $operator => $typeName) {
            $className = __NAMESPACE__ . "\\$typeName";
            if($compareType) {
                /** @var Selector $className */
                if(!($className::getCompareType() & $options['compareType'])) continue;
            }
            if($valueType === 'class') {
                $value = $typeName;
            } else if($valueType === 'className') {
                $value = $className;
            } else if($valueType === 'label') {
                $value = $className::getLabel();
            } else if($valueType === 'description') {
                $value = $className::getDescription();
            } else if($valueType === 'compareType') {
                $value = $className::getCompareType();
            } else if($valueType === 'verbose') {
                $value = array(
                    'operator' => $operator,
                    'class' => $typeName,
                    'className' => $className,
                    'compareType' => $className::getCompareType(),
                    'label' => $className::getLabel(),
                    'description' => $className::getDescription(), 
                );
            } else {
                $value = $operator;
            }
            if($indexType === 'none') {
                $key = '';
            } else if($indexType === 'class') {
                $key = $typeName;
            } else if($indexType === 'className') {
                $key = $className;
            } else {
                $key = $operator;
            }
            if($key === '') {
                $operators[] = $value;
            } else {
                $operators[$key] = $value;
            }
        }

        if(!empty($options['operator'])) return reset($operators);

        return $operators;
    }

    /**
     * Return array of all valid operator characters
     *
     * #pw-group-static-helpers
     *
     * @return array
     *
     */
    static public function getOperatorChars() {
        return self::$operatorChars;
    }

    /**
     * Return array of other characters that have meaning in a selector outside of operators
     *
     * #pw-group-static-helpers
     *
     * @return array
     * @since 3.0.156
     *
     */
    static public function getReservedChars() {
        return array(
            'or' => '|', // title|body=foo, summary=bar|baz
            'not' => '!', // !body*=suchi tobiko
            'separator' => ',', // foo=bar, bar=baz
            'match-same-1' => '@', // @foo.bar=123, @foo.baz=456
            'quote-value' => '"', // foo="bar"
            'or-group-open' => '(', // id>0, (title=foo), (body=bar)
            'or-group-close' => ')',
            'sub-selector-open' => '[', // foo=[bar>0, baz%=text]
            'sub-selector-close' => ']',
            'api-var-open' => '[', // [page], [page.id], [user.id], etc. 
            'api-var-close' => ']',
        );
    }

    /**
     * Return a string indicating the type of operator that it is, or false if not an operator
     *
     * #pw-group-static-helpers
     *
     * @param string $operator Operator to check
     * @param bool $is Change return value to just boolean true or false.
     * @return bool|string
     * @since 3.0.108
     *
     */
    static public function getOperatorType($operator, $is = false) {
        if(!isset(self::$selectorTypes[$operator])) return false;
        $type = self::$selectorTypes[$operator];
        // now double check that we can map it back, in case PHP filters anything in the isset()
        $op = array_search($type, self::$selectorTypes);
        if($op === $operator) {
            if($is) return true;
            // Convert types like "SelectorEquals" to "Equals"
            if(strpos($type, 'Selector') === 0) list(,$type) = explode('Selector', $type, 2);
            return $type;
        }
        return false;
    }

    /**
     * Given an operator, return Selector instance (or other requested Selector property)
     *
     * When getting a Selector instance, be sure to populate its `field` and `value` properties after retrieving it.
     *
     * #pw-group-static-helpers
     *
     * @param string $operator Operator to get Selector instance for
     * @param string $property One of 'instance,', 'label', 'compareType', 'class', 'className' (default='instance')
     * @return Selector|int|string|false Returns false if operator or property not recognized
     * @since 3.0.160
     *
     */
    static public function getSelectorByOperator($operator, $property = 'instance') {
        if(!isset(self::$selectorTypes[$operator])) return false;
        $typeName = self::$selectorTypes[$operator];
        /** @var Selector $className */
        $className = __NAMESPACE__ . "\\$typeName";
        if($property === 'instance' || $property === '') return new $className('', null);
        if($property === 'compareType') return $className::getCompareType();
        if($property === 'className') return $className;
        if($property === 'label') return $className::getLabel();
        if($property === 'class') return $typeName;
        return false;
    }

    /**
     * Returns true if given string is a recognized operator, or false if not
     *
     * #pw-group-static-helpers
     *
     * @param string $operator
     * @param bool $returnOperator Return the operator rather than bool? When true, corrects minor typos, like mixed up
     *   order, returning correct found operator string if possible, false otherwise. Added 3.0.162. (default=false)
     * @return bool|string
     * @since 3.0.108
     *
     */
    static public function isOperator($operator, $returnOperator = false) {
        $is = self::getOperatorType($operator, true);
        if(!$returnOperator || strlen($operator) < 3) return $is;
        if($is) return $operator;
        $op = strrev(trim($operator, '=')) . '=';
        return self::getOperatorType($op, true) ? $op : false;
    }

    /**
     * Does the given string have an operator in it?
     *
     * #pw-group-static-helpers
     *
     * @param string $str String that might contain an operator
     * @param bool $getOperator Specify true to return the operator that was found, or false if not (since 3.0.108)
     * @return bool
     *
     */
    static public function stringHasOperator($str, $getOperator = false) {

        static $letters = 'abcdefghijklmnopqrstuvwxyz';
        static $digits = '_0123456789';

        $has = false;
        $str = (string) $str;

        foreach(self::$selectorTypes as $operator => $unused) {

            if($operator == '&') continue; // this operator is too common in other contexts

            $pos = strpos($str, $operator);
            if(!$pos) continue; // if pos is 0 or false, move onto the next

            // possible match: confirm that field name precedes an operator
            // if(preg_match('/\b[_a-zA-Z0-9]+' . preg_quote($operator) . '/', $str)) {

            $c = $str[$pos-1]; // letter before the operator

            if(stripos($letters, $c) !== false) {
                // if a letter appears as the character before operator, then we're good
                $has = true;

            } else if(strpos($digits, $c) !== false) {
                // if a digit appears as the character before operator, we need to confirm there is at least one letter
                // as there can't be a field named 123, for example, which would mean the operator is likely something 
                // to do with math equations, which we would refuse as a valid selector operator
                $n = $pos-1;
                while($n > 0) {
                    $c = $str[--$n];
                    if(stripos($letters, $c) !== false) {
                        // if found a letter, then we've got something valid
                        $has = true;
                        break;

                    } else if(strpos($digits, $c) === false) {
                        // if we've got a non-digit (and non-letter) then definitely not valid
                        break;
                    }
                }
            }

            if($has) {
                if($getOperator) $getOperator = $operator;
                break;
            }
        }

        if($has && $getOperator) return $getOperator;

        return $has;
    }

    /**
     * Is the given string a Selector string?
     *
     * #pw-group-static-helpers
     *
     * @param string $str String to check for selector(s)
     * @return bool
     *
     */
    static public function stringHasSelector($str) {

        if(!self::stringHasOperator($str)) return false;

        $has = false;
        $alphabet = 'abcdefghijklmnopqrstuvwxyz';

        // replace characters that are allowed but aren't useful here
        if(strpos($str, '=(') !== false) $str = str_replace('=(', '=1,', $str);
        $str = str_replace(array('!', '(', ')', '@', '.', '|', '_'), '', trim(strtolower($str)));

        // flatten sub-selectors
        $pos = strpos($str, '[');
        if($pos && strrpos($str, ']') > $pos) {
            $str = str_replace(array(']', '=[', '<[', '>['), array('', '=1,', '<2,', '>3,'), $str);
        }
        $str = rtrim($str, ", ");

        // first character must match alphabet
        if(strpos($alphabet, substr($str, 0, 1)) === false) return false;

        $operatorChars = implode('', self::getOperatorChars());

        if(strpos($str, ',')) {
            // split the string into all key=value components and check each individually
            $inQuote = '';
            $cLast = '';
            // replace comments in quoted values so that they aren't considered selector boundaries
            for($n = 0; $n < strlen($str); $n++) {
                $c = $str[$n];
                if($c === ',') {
                    // commas in quoted values are replaced with semicolons
                    if($inQuote) $str[$n] = ';';
                } else if(($c === '"' || $c === "'") && $cLast != "\\") {
                    if($inQuote && $inQuote === $c) {
                        $inQuote = ''; // end quote
                    } else if(!$inQuote) {
                        $inQuote = $c; // start quote
                    }
                }
                $cLast = $c;
            }
            $parts = explode(',', $str);
        } else {
            // outside of verbose mode, only the first apparent selector is checked
            $parts = array($str);
        }

        // check each key=value component
        foreach($parts as $part) {
            $has = preg_match('/^[a-z][a-z0-9]*([' . $operatorChars . ']+)(.*)$/', trim($part), $matches);
            if($has) {
                $operator = $matches[1];
                $value = $matches[2];
                if(!isset(self::$selectorTypes[$operator])) {
                    $has = false;
                } else if(self::stringHasOperator($value) && $value[0] != '"' && $value[0] != "'") {
                    // operators not allowed in values unless quoted
                    $has = false;
                }
            }
            if(!$has) break;
        }

        return $has;
    }

    /**
     * Does given selector have given field (and optionally operator and/or value)?
     * 
     * #pw-group-static-helpers
     * 
     * @param string|array|Selectors $selectors Selector string, array or Selectors object to look in
     * @param string|array $fieldName Field name string to match or array of them to match any one of them
     * @param array $options
     *  - `verbose` (bool): Return associative array with verbose result? See return value. (default=false)
     *  - `operator` (string): Require this operator (default='' for any) 
     *  - `value` (string|int): Require this value (default=null for any)
     *  - `remove` (bool): Remove matched Selector from Selectors returned in verbose result? (default=false)
     * @return array|bool True of has field, false if not, or array with the following if 'verbose' option requested:
     *  - `result` (bool): Did it match (true or false)
     *  - `selector` (Selector|null): Selector object that matched (only if result is true)
     *  - `selectors` (Selectors|null): Selectors object that was analyzed or null if not needed
     *  - `field` (string): Field name that matched
     *  - `operator` (string): Operator that matched
     *  - `value` (string|null): Value that matched or null if not applicable
     * @since 3.0.174
     * 
     */
    static public function selectorHasField($selectors, $fieldName, array $options = array()) { 
        
        $defaults = array(
            'operator' => '', // require this operator
            'value' => null, // require this value
            'verbose' => false, // return verbose information?
            'remove' => false, // remove matched Selector from Selectors (when/if applicable)
        );
        
        $result = array(
            'result' => false, // true if field found, false if not
            'selectors' => null,  // Selectors object when used
            'selector' => null, // first Selector that matched
            'field' => '', // field name that matched
            'operator' => '', // operator that matched
            'value' => null, // value that matched or null if not applicable
        );

        $options = count($options) ? array_merge($defaults, $options) : $defaults;
        $fail = false;
        
        if(is_array($selectors)) {
            $selectors = new Selectors($selectors);
            
        } else if(is_string($selectors)) {
            if(is_array($fieldName)) {
                foreach($fieldName as $key => $name) {
                    if(strpos($selectors, $name) === false) unset($fieldName[$key]);
                }
                $count = count($fieldName);
                $fail = $count === 0;
                if($count === 1) $fieldName = reset($fieldName); // simplify 1-item array to string
            } else if(strpos($selectors, $fieldName) === false) {
                $fail = true;
            }
            
        } else if(!$selectors instanceof Selectors) {
            $fail = true;
        }
        
        if($fail) {
            return ($options['verbose'] ? $result : $result['result']);
        }
        
        if(!$selectors instanceof Selectors) {
            $selectors = new Selectors($selectors);
        }
        
        /** @var Selectors $selectors */
        foreach($selectors as $selector) {
            
            if($options['operator'] && $selector->operator() !== $options['operator']) continue;
            
            $field = $selector->field;
        
            // require specific field or one of array of fields to match
            if(is_string($field)) {
                // field is string
                if(is_array($fieldName)) {
                    // find field in fieldName array
                    if(!in_array($field, $fieldName)) continue;
                } else {
                    // both field and fieldName are strings
                    if($field !== $fieldName) continue;
                }
            } else if(is_array($field)) {
                // field is array
                if(is_array($fieldName)) {
                    // both field and fieldName are arrays
                    $has = false;
                    foreach($fieldName as $name) {
                        $has = in_array($name, $field) ? $name : false;
                        if($has) break;
                    }
                    if(!$has) continue;
                    $field = $has;
                } else {
                    // find fieldName in field array
                    $key = array_search($fieldName, $field);
                    if($key === false) continue;
                    $field = $field[$key];
                }
            } else {
                // field in unrecognized format (should not be reachable)
                continue;
            }
            
            if($options['value'] !== null) {
                // require specific value to match
                $value = $selector->value;
                if(is_array($value)) {
                    if(!in_array($options['value'], $value)) continue;
                    // match success
                    $result['value'] = $options['value'];
                } else {
                    if("$value" !== "$options[value]") continue;
                    // match success
                    $result['value'] = $value;
                }
            } else {
                // match success
                $result['value'] = $selector->value;
            }
            
            if($options['remove']) $selectors->remove($selector);
            
            $result = array_merge($result, array(
                'result' => true, 
                'selectors' => $selectors, 
                'selector' => $selector, 
                'field' => $field, 
                'operator' => $selector->operator(), 
            ));
            
            break;
        }
        
        return ($options['verbose'] ? $result : $result['result']);
    }

    /**
     * Simple "a=b, c=d" selector-style string conversion to associative array, for fast/simple needs
     *
     * - The only supported operator is "=".
     * - Each key=value statement should be separated by a comma.
     * - Do not use quoted values.
     * - If you need a literal comma, use a double comma ",,".
     * - If you need a literal equals, use a double equals "==".
     *
     * #pw-group-static-helpers
     *
     * @param string $s
     * @return array
     *
     */
    static public function keyValueStringToArray($s) {

        if(strpos($s, '~~COMMA') !== false) $s = str_replace('~~COMMA', '', $s);
        if(strpos($s, '~~EQUAL') !== false) $s = str_replace('~~EQUAL', '', $s);

        $hasEscaped = false;

        if(strpos($s, ',,') !== false) {
            $s = str_replace(',,', '~~COMMA', $s);
            $hasEscaped = true;
        }
        if(strpos($s, '==') !== false) {
            $s = str_replace('==', '~~EQUAL', $s);
            $hasEscaped = true;
        }

        $a = array();
        $parts = explode(',', $s);
        foreach($parts as $part) {
            if(!strpos($part, '=')) continue;
            list($key, $value) = explode('=', $part);
            if($hasEscaped) $value = str_replace(array('~~COMMA', '~~EQUAL'), array(',', '='), $value);
            $a[trim($key)] = trim($value);
        }

        return $a;
    }

    /**
     * Given an assoc array, convert to a key=value selector-style string
     *
     * #pw-group-static-helpers
     *
     * @param array $a
     * @return string
     *
     */
    static public function arrayToKeyValueString($a) {
        $s = '';
        foreach($a as $key => $value) {
            if(strpos($value, ',') !== false) $value = str_replace(array(',,', ','), ',,', $value);
            if(strpos($value, '=') !== false) $value = str_replace('=', '==', $value);
            $s .= "$key=$value, ";
        }
        return rtrim($s, ", ");
    }


}

Selector::loadSelectorTypes();