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<?php
namespace TeamTNT\TNTSearch\Stemmer;
/**
* Copyright (c) 2013 Aris Buzachis (buzachis.aris@gmail.com)
*
* All rights reserved.
*
* This script is free software.
*
* DISCLAIMER:
*
* IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
* ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/**
* Takes a word and reduces it to its German stem using the Porter stemmer algorithm.
*
* References:
* - http://snowball.tartarus.org/algorithms/porter/stemmer.html
* - http://snowball.tartarus.org/algorithms/german/stemmer.html
*
* Usage:
* $stem = GermanStemmer::stem($word);
*
* @author Aris Buzachis <buzachis.aris@gmail.com>
* @author Pascal Landau <kontakt@myseosolution.de>
*/
class GermanStemmer implements Stemmer
{
/**
* R1 and R2 regions (see the Porter algorithm)
*/
private static $R1;
private static $R2;
private static $cache = array();
private static $vowels = array('a', 'e', 'i', 'o', 'u', 'y', 'ä', 'ö', 'ü');
private static $s_ending = array('b', 'd', 'f', 'g', 'h', 'k', 'l', 'm', 'n', 'r', 't');
private static $st_ending = array('b', 'd', 'f', 'g', 'h', 'k', 'l', 'm', 'n', 't');
/**
* Gets the stem of $word.
* @param string $word
* @return string
*/
public static function stem($word)
{
$word = mb_strtolower($word);
//check for invalid characters
preg_match("#.#u", $word);
if (preg_last_error() !== 0) {
throw new \InvalidArgumentException("Word '$word' seems to be errornous. Error code from preg_last_error(): " . preg_last_error());
}
if (!isset(self::$cache[$word])) {
$result = self::getStem($word);
self::$cache[$word] = $result;
}
return self::$cache[$word];
}
/**
* @param $word
* @return string
*/
private static function getStem($word)
{
$word = self::step0a($word);
$word = self::step1($word);
$word = self::step2($word);
$word = self::step3($word);
$word = self::step0b($word);
return $word;
}
/**
* Replaces to protect some characters
* @param string $word
* @return string mixed
*/
private static function step0a($word)
{
$vstr = implode('', self::$vowels);
$word = preg_replace('#([' . $vstr . '])u([' . $vstr . '])#u', '$1U$2', $word);
$word = preg_replace('#([' . $vstr . '])y([' . $vstr . '])#u', '$1Y$2', $word);
return $word;
}
/**
* Undo the initial replaces
* @param string $word
* @return string
*/
private static function step0b($word)
{
$word = str_replace(array('ä', 'ö', 'ü', 'U', 'Y'), array('a', 'o', 'u', 'u', 'y'), $word);
return $word;
}
private static function step1($word)
{
$word = str_replace('ß', 'ss', $word);
self::getR($word);
$replaceCount = 0;
$arr = array('em', 'ern', 'er');
foreach ($arr as $s) {
self::$R1 = preg_replace('#' . $s . '$#u', '', self::$R1, -1, $replaceCount);
if ($replaceCount > 0) {
$word = preg_replace('#' . $s . '$#u', '', $word);
}
}
$arr = array('en', 'es', 'e');
foreach ($arr as $s) {
self::$R1 = preg_replace('#' . $s . '$#u', '', self::$R1, -1, $replaceCount);
if ($replaceCount > 0) {
$word = preg_replace('#' . $s . '$#u', '', $word);
$word = preg_replace('#niss$#u', 'nis', $word);
}
}
$word = preg_replace('/([' . implode('', self::$s_ending) . '])s$/u', '$1', $word);
return $word;
}
private static function step2($word)
{
self::getR($word);
$replaceCount = 0;
$arr = array('est', 'er', 'en');
foreach ($arr as $s) {
self::$R1 = preg_replace('#' . $s . '$#u', '', self::$R1, -1, $replaceCount);
if ($replaceCount > 0) {
$word = preg_replace('#' . $s . '$#u', '', $word);
}
}
if (strpos(self::$R1, 'st') !== false) {
self::$R1 = preg_replace('#st$#u', '', self::$R1);
$word = preg_replace('#(...[' . implode('', self::$st_ending) . '])st$#u', '$1', $word);
}
return $word;
}
private static function step3($word)
{
self::getR($word);
$replaceCount = 0;
$arr = array('end', 'ung');
foreach ($arr as $s) {
if (preg_match('#' . $s . '$#u', self::$R2)) {
$word = preg_replace('#([^e])' . $s . '$#u', '$1', $word, -1, $replaceCount);
if ($replaceCount > 0) {
self::$R2 = preg_replace('#' . $s . '$#u', '', self::$R2, -1, $replaceCount);
}
}
}
$arr = array('isch', 'ik', 'ig');
foreach ($arr as $s) {
if (preg_match('#' . $s . '$#u', self::$R2)) {
$word = preg_replace('#([^e])' . $s . '$#u', '$1', $word, -1, $replaceCount);
if ($replaceCount > 0) {
self::$R2 = preg_replace('#' . $s . '$#u', '', self::$R2);
}
}
}
$arr = array('lich', 'heit');
foreach ($arr as $s) {
self::$R2 = preg_replace('#' . $s . '$#u', '', self::$R2, -1, $replaceCount);
if ($replaceCount > 0) {
$word = preg_replace('#' . $s . '$#u', '', $word);
} else {
if (preg_match('#' . $s . '$#u', self::$R1)) {
$word = preg_replace('#(er|en)' . $s . '$#u', '$1', $word, -1, $replaceCount);
if ($replaceCount > 0) {
self::$R1 = preg_replace('#' . $s . '$#u', '', self::$R1);
}
}
}
}
$arr = array('keit');
foreach ($arr as $s) {
self::$R2 = preg_replace('#' . $s . '$#u', '', self::$R2, -1, $replaceCount);
if ($replaceCount > 0) {
$word = preg_replace('#' . $s . '$#u', '', $word);
}
}
return $word;
}
/**
* Find R1 and R2
* @param string $word
*/
private static function getR($word)
{
self::$R1 = "";
self::$R2 = "";
$vowels = implode("", self::$vowels);
$vowelGroup = "[{$vowels}]";
$nonVowelGroup = "[^{$vowels}]";
// R1 is the region after the first non-vowel following a vowel, or is the null region at the end of the word if there is no such non-vowel.
$pattern = "#(?P<rest>.*?{$vowelGroup}{$nonVowelGroup})(?P<r>.*)#u";
if (preg_match($pattern, $word, $match)) {
$rest = $match["rest"];
$r1 = $match["r"];
// [...], but then R1 is adjusted so that the region before it contains at least 3 letters.
$cutOff = 3 - mb_strlen($rest);
if ($cutOff > 0) {
$r1 = mb_substr($r1, $cutOff);
}
self::$R1 = $r1;
}
//R2 is the region after the first non-vowel following a vowel in R1, or is the null region at the end of the word if there is no such non-vowel.
if (preg_match($pattern, self::$R1, $match)) {
self::$R2 = $match["r"];
}
}
}