PhutilContextFreeGrammar.php
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	<?php

	/**
	* Generate nonsense test data according to a context-free grammar definition.
	*/
	abstract class PhutilContextFreeGrammar {

	private $limit = 65535;

	abstract protected function getRules();

	public function generate() {
	$count = 0;
	return $this->applyRules('[start]', $count);
	}

	public function applyRules($input, &$count) {
	$rules = $this->getRules();

	if (++$count > $this->limit) {
	throw new Exception("Token replacement count exceeded limit!");
	}

	$matches = null;
	preg_match_all('/(\\[[^\\]]+\\])/', $input, $matches, PREG_OFFSET_CAPTURE);

	foreach (array_reverse($matches[1]) as $token_spec) {
	list($token, $offset) = $token_spec;
	$token_name = substr($token, 1, -1);

	if (empty($rules[$token_name])) {
	throw new Exception("Invalid token '{$token_name}' in grammar.");
	}

	$key = array_rand($rules[$token_name]);
	$replacement = $this->applyRules($rules[$token_name][$key], $count);

	$input = substr_replace($input, $replacement, $offset, strlen($token));
	}

	return $input;
	}

	}