/**
	* Splits keywords entered by a user into an array of words stored in $this->split_words
	*
	* @param string $keywords Contains the keyword as entered by the user
	* @param string $terms is either 'all' or 'any'
	* @return boolean false if no valid keywords were found and otherwise true
	*/
	function split_keywords(&$keywords, $terms)
	{
		global $db, $config, $user;

		// $keywords input format: each word seperated by a space, words in a bracket are not seperated

		// the user wants to search for any word, convert the search query
		if ($terms == 'any')
		{
			$words = array();
			preg_match_all('#([^\\s+\\-|()]+)(?:$|[\\s+\\-|()])#', $keywords, $words);
			if (sizeof($words))
			{
				$keywords = '(' . implode('|', $words) . ')';
			}
		}

		// generate the split_words array shown to the user
		$this->split_words = explode(' ', $keywords);

		$exact_words = array();
		preg_match_all('#([^\\s+\\-|*()]+)(?:$|[\\s+\\-|()])#', $keywords, $exact_words);

		if (sizeof($exact_words[1]))
		{
			$exact_words = $exact_words[1];

			// start with building a query to retrieve all word ids
			$where_sql = array();
			foreach ($exact_words as $i => $word)
			{
				$exact_words[$i] = '\'' . $db->sql_escape($word) . '\'';
			}

			// we can match exact words with one IN
			$sql = 'SELECT word_text, word_id
				FROM ' . SEARCH_WORDLIST_TABLE . '
				WHERE word_text IN (' . implode(', ', $exact_words) . ')';
			$result = $db->sql_query($sql);
	
			// replace text with ids and prefix ids with #
			while ($row = $db->sql_fetchrow($result))
			{
				$words[$row['word_text']] = (int) $row['word_id'];
			}
			$db->sql_freeresult($result);
		}
		unset($exact_words);

		// now analyse the search query, first split it using the spaces
		$query = explode(' ', $keywords);

		$this->must_contain_ids = array();
		$this->must_not_contain_ids = array();
		$this->must_exclude_one_ids = array();

		$mode = '';
		$ignore_no_id = true;

		foreach ($query as $word)
		{
			// words which should not be included
			if ($word[0] == '-')
			{
				$word = substr($word, 1);

				// a group of which at least one may not be in the resulting posts
				if ($word[0] == '(')
				{
					$word = explode('|', substr($word, 1, -1));
					$mode = 'exclude_one';
				}
				// one word which should not be in the resulting posts
				else
				{
					$mode = 'must_not_contain';
				}
				$ignore_no_id = true;
			}
			// words which have to be included
			else
			{
				// no prefix is the same as a +prefix
				if ($word[0] == '+')
				{
					$word = substr($word, 1);
				}

				// a group of words of which at least one word should be in every resulting post
				if ($word[0] == '(')
				{
					$word = explode('|', substr($word, 1, -1));
				}
				$ignore_no_id = false;
				$mode = 'must_contain';
			}

			// if this is an array of words then retrieve an id for each
			if (is_array($word))
			{
				$id_words = array();
				foreach ($word as $i => $word_part)
				{
					if (isset($words[$word_part]))
					{
						$id_words[] = $words[$word_part];
					}
				}
				if (sizeof($id_words))
				{
					$id_words = array_values($id_words);
					switch ($mode)
					{
						case 'exclude_one':
							if (sizeof($ids > 1))
							{
								$this->must_exclude_one_ids[] = $id_words;
							}
							else
							{
								$this->must_not_contain_ids[] = $id_words[0];
							}
						break;
						case 'must_contain':
							$this->must_contain_ids[] = (sizeof($id_words > 1)) ? $id_words : $id_words[0];
						break;
					}
				}
				// throw an error if we shall not ignore unexistant words
				else if (!$ignore_no_id)
				{
					trigger_error(sprintf($user->lang['WORDS_IN_NO_POST'], implode(', ', $word)));
				}
			}
			// else we only need one id
			else if (isset($words[$word]))
			{
				switch ($mode)
				{
					case 'must_not_contain':
						$this->must_not_contain_ids[] = $words[$word];
					break;
					case 'must_contain':
						$this->must_contain_ids[] = $words[$word];
					break;
				}
			}
			// throw an error if we shall not ignore unexistant words
			else if (!$ignore_no_id)
			{
				trigger_error(sprintf($user->lang['WORD_IN_NO_POST'], $word));
			}
		}

		// we can't search for negatives only
		if (!sizeof($this->must_contain_ids))
		{
			return false;
		}

		if (sizeof($this->split_words))
		{
			$this->split_words = array_values($this->split_words);
			return true;
		}
		return false;
	}