private function _generateIndex ($group, $id)
	{
		switch ($group) {
			case 'custom':
				$last = DateTimeHelper::toIso8601(
					SitemapRecord::find()->one()->dateUpdated
				);
				$pages = 1;
				break;

			case 'sections':
				$last = $this->_getUpdated(Entry::instance(), $id);
				$pages = $this->_getPageCount(Entry::instance(), $id);
				break;

			case 'categories':
				$last = $this->_getUpdated(Category::instance(), $id);
				$pages = $this->_getPageCount(Category::instance(), $id);
				break;

			default:
				$last = DateTimeHelper::currentUTCDateTime()->format('c');
				$pages = 1;
		}

		for ($i = 0; $i < $pages; ++$i)
		{
			$sitemap = $this->_document->createElement('sitemap');
			$this->_index->appendChild($sitemap);

			$loc = $this->_document->createElement(
				'loc',
				$this->_indexUrl($group, $id, $i)
			);
			$sitemap->appendChild($loc);

			$lastMod = $this->_document->createElement('lastmod', $last);
			$sitemap->appendChild($lastMod);
		}
	}
private function _generateIndex ($group, $id)
	{
		switch ($group) {
			case 'custom':
				$last = DateTimeHelper::toIso8601(
					SitemapRecord::find()->one()->dateUpdated
				);
				$pages = 1;
				break;

			case 'sections':
				$last = $this->_getUpdated(Entry::instance(), $id);
				$pages = $this->_getPageCount(Entry::instance(), $id);
				break;

			case 'categories':
				$last = $this->_getUpdated(Category::instance(), $id);
				$pages = $this->_getPageCount(Category::instance(), $id);
				break;

			default:
				$last = DateTimeHelper::currentUTCDateTime()->format('c');
				$pages = 1;
		}

		for ($i = 0; $i < $pages; ++$i)
		{
			$sitemap = $this->_document->createElement('sitemap');
			$this->_index->appendChild($sitemap);

			$loc = $this->_document->createElement(
				'loc',
				$this->_indexUrl($group, $id, $i)
			);
			$sitemap->appendChild($loc);

			$lastMod = $this->_document->createElement('lastmod', $last);
			$sitemap->appendChild($lastMod);
		}
	}
@param $group
@param $id

@throws \yii\base\Exception