public function main()
    {
        if ($this->useSass) {
            if (strlen($this->executable) < 0) {
                throw new BuildException("'executable' must be defined.");
            }
        }

        if (empty($this->filesets) && $this->file === null) {
            throw new BuildException(
                "Missing either a nested fileset or attribute 'file'"
            );
        }

        try {
            $compiler = (new SassTaskCompilerFactory(FileSystem::getFileSystem()))->prepareCompiler($this);
        } catch (BuildException $exception) {
            if ($this->failonerror) {
                throw $exception;
            }
            $this->log($exception->getMessage());
            return;
        }

        if (count($this->filesets) > 0) {
            $this->processFilesets($compiler);
        } elseif ($this->file !== null) {
            $this->processFile($compiler);
        }
    }