*
	 * @return WP_Error|array WP_Error on error or array containing html template of the first question.
	 */
	public static function quiz_start( $request ) {

		$err = new WP_Error();

		$student = llms_get_student();
		if ( ! $student ) {
			$err->add( 400, __( 'You must be logged in to take quizzes.', 'lifterlms' ) );
			return $err;
		}

		// Limit reached?
		if ( isset( $request['quiz_id'] ) && ! ( new LLMS_Quiz( $request['quiz_id'] ) )->is_open() ) {
			$err->add( 400, __( "You've reached the maximum number of attempts for this quiz.", 'lifterlms' ) );
			return $err;
		}

		$attempt = false;
		if ( ! empty( $request['attempt_key'] ) ) {
			$attempt = $student->quizzes()->get_attempt_by_key( $request['attempt_key'] );
		}

		if ( ! $attempt || 'new' !== $attempt->get_status() ) {

			if ( ! isset( $request['quiz_id'] ) || ! isset( $request['lesson_id'] ) ) {
				$err->add( 400, __( 'There was an error starting the quiz. Please return to the lesson and begin again.', 'lifterlms' ) );
				return $err;
			}

			$attempt = LLMS_Quiz_Attempt::init( absint( $request['quiz_id'] ), absint( $request['lesson_id'] ), $student->get( 'id' ) );

		}

		$question_id = $attempt->get_first_question();
		if ( ! $question_id ) {
			$err->add( 404, __( 'Unable to start quiz because the quiz does not contain any questions.', 'lifterlms' ) );
			return $err;
		}

		$attempt->start();
		$html = llms_get_template_ajax(
			'content-single-question.php',
			array(
				'attempt'  => $attempt,
				'question' => llms_get_post( $question_id ),
			)
		);

		$quiz  = $attempt->get_quiz();
		$limit = $quiz->has_time_limit() ? $quiz->get( 'time_limit' ) : false;

		return array(
			'attempt_key' => $attempt->get_key(),
			'html'        => $html,
			'time_limit'  => $limit,
			'question_id' => $question_id,
			'total'       => $attempt->get_count( 'questions' ),