core-bundle/src/Resources/contao/classes/StyleSheets.php
public function checkStyleSheetName($strName)
	{
		$objStyleSheet = $this->Database->prepare("SELECT COUNT(*) AS count FROM tl_style_sheet WHERE name=?")
										->limit(1)
										->execute($strName);

		if ($objStyleSheet->count < 1)
		{
			return $strName;
		}

		$chunks = explode('-', $strName);
		$i = (\count($chunks) > 1) ? array_pop($chunks) : 0;
		$strName = implode('-', $chunks) . '-' . ((int) $i + 1);

		return $this->checkStyleSheetName($strName);
	}
public function checkStyleSheetName($strName)
	{
		$objStyleSheet = $this->Database->prepare("SELECT COUNT(*) AS count FROM tl_style_sheet WHERE name=?")
										->limit(1)
										->execute($strName);

		if ($objStyleSheet->count < 1)
		{
			return $strName;
		}

		$chunks = explode('-', $strName);
		$i = (\count($chunks) > 1) ? array_pop($chunks) : 0;
		$strName = implode('-', $chunks) . '-' . ((int) $i + 1);

		return $this->checkStyleSheetName($strName);
	}
Check the name of an imported file

@param string $strName

@return string