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New libraries to support lexer-based searching. From Tony Hursh - tha…
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…nks!
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moodler committed Jan 31, 2005
1 parent b2432b7 commit 792a590
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393 changes: 393 additions & 0 deletions lib/lexer.php
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<?php // $Id$

/* PHP lexer code snarfed from the CVS tree for the lamplib project at
* http://sourceforge.net/projects/lamplib
* This project is administered by Markus Baker, Harry Fuecks and Matt
* Mitchell, and the project code is in the public domain.
*
* Thanks, guys!
*/

define("LEXER_ENTER", 1);
define("LEXER_MATCHED", 2);
define("LEXER_UNMATCHED", 3);
define("LEXER_EXIT", 4);
define("LEXER_SPECIAL", 5);

/**
* Compounded regular expression. Any of
* the contained patterns could match and
* when one does it's label is returned.
*/
class ParallelRegex {
var $_patterns;
var $_labels;
var $_regex;
var $_case;

/**
* Constructor. Starts with no patterns.
* @param $case True for case sensitive, false
* for insensitive.
* @public
*/
function ParallelRegex($case) {
$this->_case = $case;
$this->_patterns = array();
$this->_labels = array();
$this->_regex = null;
}

/**
* Adds a pattern with an optional label.
* @param $pattern Perl style regex, but ( and )
* lose the usual meaning.
* @param $label Label of regex to be returned
* on a match.
* @public
*/
function addPattern($pattern, $label = true) {
$count = count($this->_patterns);
$this->_patterns[$count] = $pattern;
$this->_labels[$count] = $label;
$this->_regex = null;
}

/**
* Attempts to match all patterns at once against
* a string.
* @param $subject String to match against.
* @param $match First matched portion of
* subject.
* @return True on success.
* @public
*/
function match($subject, &$match) {
if (count($this->_patterns) == 0) {
return false;
}
if (!preg_match($this->_getCompoundedRegex(), $subject, $matches)) {
$match = "";
return false;
}
$match = $matches[0];
for ($i = 1; $i < count($matches); $i++) {
if ($matches[$i]) {
return $this->_labels[$i - 1];
}
}
return true;
}

/**
* Compounds the patterns into a single
* regular expression separated with the
* "or" operator. Caches the regex.
* Will automatically escape (, ) and / tokens.
* @param $patterns List of patterns in order.
* @private
*/
function _getCompoundedRegex() {
if ($this->_regex == null) {
for ($i = 0; $i < count($this->_patterns); $i++) {
$this->_patterns[$i] = '(' . str_replace(
array('/', '(', ')'),
array('\/', '\(', '\)'),
$this->_patterns[$i]) . ')';
}
$this->_regex = "/" . implode("|", $this->_patterns) . "/" . $this->_getPerlMatchingFlags();
}
return $this->_regex;
}

/**
* Accessor for perl regex mode flags to use.
* @return Flags as string.
* @private
*/
function _getPerlMatchingFlags() {
return ($this->_case ? "msS" : "msSi");
}
}

/**
* States for a stack machine.
*/
class StateStack {
var $_stack;

/**
* Constructor. Starts in named state.
* @param $start Starting state name.
* @public
*/
function StateStack($start) {
$this->_stack = array($start);
}

/**
* Accessor for current state.
* @return State as string.
* @public
*/
function getCurrent() {
return $this->_stack[count($this->_stack) - 1];
}

/**
* Adds a state to the stack and sets it
* to be the current state.
* @param $state New state.
* @public
*/
function enter($state) {
array_push($this->_stack, $state);
}

/**
* Leaves the current state and reverts
* to the previous one.
* @return False if we drop off
* the bottom of the list.
* @public
*/
function leave() {
if (count($this->_stack) == 1) {
return false;
}
array_pop($this->_stack);
return true;
}
}

/**
* Accepts text and breaks it into tokens.
* Some optimisation to make the sure the
* content is only scanned by the PHP regex
* parser once. Lexer modes must not start
* with leading underscores.
*/
class Lexer {
var $_regexes;
var $_parser;
var $_mode;
var $_mode_handlers;
var $_case;

/**
* Sets up the lexer in case insensitive matching
* by default.
* @param $parser Handling strategy by
* reference.
* @param $start Starting handler.
* @param $case True for case sensitive.
* @public
*/
function Lexer(&$parser, $start = "accept", $case = false) {
$this->_case = $case;
$this->_regexes = array();
$this->_parser = &$parser;
$this->_mode = new StateStack($start);
$this->_mode_handlers = array();
}

/**
* Adds a token search pattern for a particular
* parsing mode. The pattern does not change the
* current mode.
* @param $pattern Perl style regex, but ( and )
* lose the usual meaning.
* @param $mode Should only apply this
* pattern when dealing with
* this type of input.
* @public
*/
function addPattern($pattern, $mode = "accept") {
if (!isset($this->_regexes[$mode])) {
$this->_regexes[$mode] = new ParallelRegex($this->_case);
}
$this->_regexes[$mode]->addPattern($pattern);
}

/**
* Adds a pattern that will enter a new parsing
* mode. Useful for entering parenthesis, strings,
* tags, etc.
* @param $pattern Perl style regex, but ( and )
* lose the usual meaning.
* @param $mode Should only apply this
* pattern when dealing with
* this type of input.
* @param $new_mode Change parsing to this new
* nested mode.
* @public
*/
function addEntryPattern($pattern, $mode, $new_mode) {
if (!isset($this->_regexes[$mode])) {
$this->_regexes[$mode] = new ParallelRegex($this->_case);
}
$this->_regexes[$mode]->addPattern($pattern, $new_mode);
}

/**
* Adds a pattern that will exit the current mode
* and re-enter the previous one.
* @param $pattern Perl style regex, but ( and )
* lose the usual meaning.
* @param $mode Mode to leave.
* @public
*/
function addExitPattern($pattern, $mode) {
if (!isset($this->_regexes[$mode])) {
$this->_regexes[$mode] = new ParallelRegex($this->_case);
}
$this->_regexes[$mode]->addPattern($pattern, "__exit");
}

/**
* Adds a pattern that has a special mode.
* Acts as an entry and exit pattern in one go.
* @param $pattern Perl style regex, but ( and )
* lose the usual meaning.
* @param $mode Should only apply this
* pattern when dealing with
* this type of input.
* @param $special Use this mode for this one token.
* @public
*/
function addSpecialPattern($pattern, $mode, $special) {
if (!isset($this->_regexes[$mode])) {
$this->_regexes[$mode] = new ParallelRegex($this->_case);
}
$this->_regexes[$mode]->addPattern($pattern, "_$special");
}

/**
* Adds a mapping from a mode to another handler.
* @param $mode Mode to be remapped.
* @param $handler New target handler.
* @public
*/
function mapHandler($mode, $handler) {
$this->_mode_handlers[$mode] = $handler;
}

/**
* Splits the page text into tokens. Will fail
* if the handlers report an error or if no
* content is consumed. If successful then each
* unparsed and parsed token invokes a call to the
* held listener.
* @param $raw Raw HTML text.
* @return True on success, else false.
* @public
*/
function parse($raw) {
if (!isset($this->_parser)) {
return false;
}
$length = strlen($raw);
while (is_array($parsed = $this->_reduce($raw))) {
list($unmatched, $matched, $mode) = $parsed;
if (!$this->_dispatchTokens($unmatched, $matched, $mode)) {
return false;
}
if (strlen($raw) == $length) {
return false;
}
$length = strlen($raw);
}
if (!$parsed) {
return false;
}
return $this->_invokeParser($raw, LEXER_UNMATCHED);
}

/**
* Sends the matched token and any leading unmatched
* text to the parser changing the lexer to a new
* mode if one is listed.
* @param $unmatched Unmatched leading portion.
* @param $matched Actual token match.
* @param $mode Mode after match. The "_exit"
* mode causes a stack pop. An
* false mode causes no change.
* @return False if there was any error
* from the parser.
* @private
*/
function _dispatchTokens($unmatched, $matched, $mode = false) {
if (!$this->_invokeParser($unmatched, LEXER_UNMATCHED)) {
return false;
}
if ($mode === "__exit") {
if (!$this->_invokeParser($matched, LEXER_EXIT)) {
return false;
}
return $this->_mode->leave();
}
if (strncmp($mode, "_", 1) == 0) {
$mode = substr($mode, 1);
$this->_mode->enter($mode);
if (!$this->_invokeParser($matched, LEXER_SPECIAL)) {
return false;
}
return $this->_mode->leave();
}
if (is_string($mode)) {
$this->_mode->enter($mode);
return $this->_invokeParser($matched, LEXER_ENTER);
}
return $this->_invokeParser($matched, LEXER_MATCHED);
}

/**
* Calls the parser method named after the current
* mode. Empty content will be ignored.
* @param $content Text parsed.
* @param $is_match Token is recognised rather
* than unparsed data.
* @private
*/
function _invokeParser($content, $is_match) {
if (($content === "") || ($content === false)) {
return true;
}
$handler = $this->_mode->getCurrent();
if (isset($this->_mode_handlers[$handler])) {
$handler = $this->_mode_handlers[$handler];
}
return $this->_parser->$handler($content, $is_match);
}

/**
* Tries to match a chunk of text and if successful
* removes the recognised chunk and any leading
* unparsed data. Empty strings will not be matched.
* @param $raw The subject to parse. This is the
* content that will be eaten.
* @return Three item list of unparsed
* content followed by the
* recognised token and finally the
* action the parser is to take.
* True if no match, false if there
* is a parsing error.
* @private
*/
function _reduce(&$raw) {
if (!isset($this->_regexes[$this->_mode->getCurrent()])) {
return false;
}
if ($raw === "") {
return true;
}
if ($action = $this->_regexes[$this->_mode->getCurrent()]->match($raw, $match)) {
$count = strpos($raw, $match);
$unparsed = substr($raw, 0, $count);
$raw = substr($raw, $count + strlen($match));
return array($unparsed, $match, $action);
}
return true;
}
}
?>
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