CWebdavDocumentHistory::OnBeforeDeleteFileFromHistory

static function OnBeforeDeleteFileFromHistory($historyId, $documentId)
{
	static $arHistoryFields = array("ID", "DOCUMENT_ID", "DOCUMENT");

	$history = new CBPHistoryService();

	if ($documentId[0] != 'webdav')
		return true;

	$fileToDeleteHash = null;

	$dbDoc = $history->GetHistoryList(
		array("ID" => "DESC"),
		array("ID" => $historyId),
		false,
		false,
		$arHistoryFields
	);

	if ($dbDoc && ($arDoc = $dbDoc->Fetch()))
	{
		if (isset($arDoc['DOCUMENT']['PROPERTIES']['FILE']['HASH']))
			$fileToDeleteHash = $arDoc['DOCUMENT']['PROPERTIES']['FILE']['HASH'];
	}

	$result = true; // seems to be an old file without hash
	if ($fileToDeleteHash != null) // if not
	{
		$dbDoc = $history->GetHistoryList(
			array("ID" => "DESC"),
			array("DOCUMENT_ID" => $documentId),
			false,
			false,
			$arHistoryFields
		);

		if ($dbDoc)
		{
			while ($arDoc = $dbDoc->Fetch())
			{
				if ($arDoc['ID'] == $historyId)
					continue;
				if (isset($arDoc['DOCUMENT']['PROPERTIES']['FILE']['HASH']))
				{
					$result = !($arDoc['DOCUMENT']['PROPERTIES']['FILE']['HASH'] == $fileToDeleteHash); // file used also in other historyRecord
					if (!$result)
						break;
				}
			}
		}

	}
	return $result;
}