GradeEnum.php

<?php

enum Grade: string
{
    case PASS = 'pass';
    case FAIL = 'fail';
    case A = 'A';
    case F = 'F';
    case INVALID = 'Invalid grade!\n';

    public function message(): string
    {
        return match ($this) {
            Grade::PASS => 'Passed in',
            Grade::FAIL => 'Failed in',
            Grade::A => 'Excellent',
            Grade::F => 'You can do better',
            Grade::INVALID => 'Invalid grade!\n',
        };
    }
}

class GradeEnum
{

    /**
     * @param $grade
     * @param $subject
     *
     * @return string
     */
    public function getGradeRemark(string $grade, string $subject = ''): string
    {
        if ($message = Grade::tryFrom($grade)) {
            return $message->message() . " $subject!\n";
        }

        return Grade::INVALID->value;
    }

}

// Required PHP version 8.1

$grade = new GradeEnum();
echo $grade->getGradeRemark('A');
#Excellent!
echo $grade->getGradeRemark('fail', 'English');
#Failed in English!
echo $grade->getGradeRemark('faisds', 'English');
#Invalid grade!!