public function addDocument(TokensDocument $document)
{
foreach ($document->getDocumentData() as $term) {
if (isset($this->index[$term])) {
$this->index[$term][self::FREQ]++;
$this->index[$term][self::POSTINGS][] = $document->getId();
} else {
$this->index[$term] = [self::FREQ => 1, self::POSTINGS => [$document->getId()]];
}
}
}