class SearchTextProcessor

class SearchTextProcessor implements SearchTextProcessorInterface {
    
    /**
     * The transliteration service.
     *
     * @var \Drupal\Component\Transliteration\TransliterationInterface
     */
    protected $transliteration;
    
    /**
     * The config factory.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * SearchTextProcessor constructor.
     *
     * @param \Drupal\Component\Transliteration\TransliterationInterface $transliteration
     *   The transliteration service.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     */
    public function __construct(TransliterationInterface $transliteration, ConfigFactoryInterface $config_factory, ModuleHandlerInterface $module_handler) {
        $this->transliteration = $transliteration;
        $this->configFactory = $config_factory;
        $this->moduleHandler = $module_handler;
    }
    
    /**
     * {@inheritdoc}
     */
    public function process(string $text, ?string $langcode = NULL) : array {
        $text = $this->analyze($text, $langcode);
        return explode(' ', $text);
    }
    
    /**
     * {@inheritdoc}
     */
    public function analyze(string $text, ?string $langcode = NULL) : string {
        // Decode entities to UTF-8.
        $text = Html::decodeEntities($text);
        // Lowercase.
        $text = mb_strtolower($text);
        // Remove diacritics.
        $text = $this->transliteration
            ->removeDiacritics($text);
        // Call an external processor for word handling.
        $this->invokePreprocess($text, $langcode);
        // Simple CJK handling.
        if ($this->configFactory
            ->get('search.settings')
            ->get('index.overlap_cjk')) {
            $text = preg_replace_callback('/[' . self::PREG_CLASS_CJK . ']+/u', [
                $this,
                'expandCjk',
            ], $text);
        }
        // To improve searching for numerical data such as dates, IP addresses
        // or version numbers, we consider a group of numerical characters
        // separated only by punctuation characters to be one piece.
        // This also means that searching for e.g. '20/03/1984' also returns
        // results with '20-03-1984' in them.
        // Readable regexp: ([number]+)[punctuation]+(?=[number])
        $text = preg_replace('/([' . self::PREG_CLASS_NUMBERS . ']+)[' . self::PREG_CLASS_PUNCTUATION . ']+(?=[' . self::PREG_CLASS_NUMBERS . '])/u', '\\1', $text);
        // Multiple dot and dash groups are word boundaries and replaced with space.
        // No need to use the unicode modifier here because 0-127 ASCII characters
        // can't match higher UTF-8 characters as the leftmost bit of those are 1.
        $text = preg_replace('/[.-]{2,}/', ' ', $text);
        // The dot, underscore and dash are simply removed. This allows meaningful
        // search behavior with acronyms and URLs. See unicode note directly above.
        $text = preg_replace('/[._-]+/', '', $text);
        // With the exception of the rules above, we consider all punctuation,
        // marks, spacers, etc, to be a word boundary.
        $text = preg_replace('/[' . Unicode::PREG_CLASS_WORD_BOUNDARY . ']+/u', ' ', $text);
        // Truncate everything to 50 characters.
        $words = explode(' ', $text);
        array_walk($words, [
            $this,
            'truncate',
        ]);
        $text = implode(' ', $words);
        return $text;
    }
    
    /**
     * Invokes hook_search_preprocess() to simplify text.
     *
     * @param string $text
     *   Text to preprocess, passed by reference and altered in place.
     * @param string|null $langcode
     *   Language code for the language of $text, if known.
     */
    protected function invokePreprocess(string &$text, ?string $langcode = NULL) : void {
        $this->moduleHandler
            ->invokeAllWith('search_preprocess', function (callable $hook, string $module) use (&$text, &$langcode) {
            $text = $hook($text, $langcode);
        });
    }
    
    /**
     * Splits CJK (Chinese, Japanese, Korean) text into tokens.
     *
     * The Search module matches exact words, where a word is defined to be a
     * sequence of characters delimited by spaces or punctuation. CJK languages
     * are written in long strings of characters, though, not split up into words.
     * So in order to allow search matching, we split up CJK text into tokens
     * consisting of consecutive, overlapping sequences of characters whose length
     * is equal to the 'minimum_word_size' variable. This tokenizing is only done
     * if the 'overlap_cjk' variable is TRUE.
     *
     * @param array $matches
     *   This function is a callback for preg_replace_callback(), which is called
     *   from self::analyze(). So, $matches is an array of regular expression
     *   matches, which means that $matches[0] contains the matched text -- a
     *   string of CJK characters to tokenize.
     *
     * @return string
     *   Tokenized text, starting and ending with a space character.
     */
    protected function expandCjk(array $matches) : string {
        $min = $this->configFactory
            ->get('search.settings')
            ->get('index.minimum_word_size');
        $str = $matches[0];
        $length = mb_strlen($str);
        // If the text is shorter than the minimum word size, don't tokenize it.
        if ($length <= $min) {
            return ' ' . $str . ' ';
        }
        $tokens = ' ';
        // Build a FIFO queue of characters.
        $chars = [];
        for ($i = 0; $i < $length; $i++) {
            // Add the next character off the beginning of the string to the queue.
            $current = mb_substr($str, 0, 1);
            $str = substr($str, strlen($current));
            $chars[] = $current;
            if ($i >= $min - 1) {
                // Make a token of $min characters, and add it to the token string.
                $tokens .= implode('', $chars) . ' ';
                // Shift out the first character in the queue.
                array_shift($chars);
            }
        }
        return $tokens;
    }
    
    /**
     * Helper function for array_walk in ::analyze().
     *
     * @param string $text
     *   The text to be truncated.
     */
    protected function truncate(string &$text) : void {
        if (is_numeric($text)) {
            $text = ltrim($text, '0');
        }
        if (mb_strlen($text) <= 50) {
            return;
        }
        $text = mb_substr($text, 0, 50);
    }

}