author add

<?php
function addEmployee($id,$firstName, $lastName, $grade){
    $maxId = 0;
    $lines = file("authors.txt");
    foreach ($lines as $line){
        $employee = explode(";", $line);
        if(int($employee[0]) > $maxId){
            $maxId = int($employee[0]);
        }
    }

    $newEmployee =($maxId + 1). $id . ";" . $firstName . ";" . $lastName . ";" . $grade .  PHP_EOL;
    file_put_contents("authors.txt", $newEmployee, FILE_APPEND);

}

if ($_SERVER["REQUEST_METHOD"] === "POST"){
    $id = $_POST["id"];
    $firstName = $_POST["firstName"];
    $lastName = $_POST["lastName"];
    $grade = $_POST["grade"];

    addEmployee($id, $firstName, $lastName, $grade);
}
?>

<!doctype html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <link rel="stylesheet" type="text/css" href="styles.css">
    <title>LisaAuthor</title>
</head>
<body id="author-form-page">

<div id="root">

    <nav>
        <div>
            <a href="../index.php" id="book-list-link">Raamatud</a>
            <a href="book-add.php" id="book-form-link">Lisa raamat</a>
            <a href="author-list.php" id="author-list-link">Autorid</a>
            <a href="author-add.php" id="author-form-link">Lisa autor</a>
        </div>

    </nav>

    <main>


        <form id="input-form" method="post">

            <input name="id" type="hidden" value="">

            <div class="label">Eesnimi:</div>
            <div class="input"><input id="firstName" name="firstName" value="" type="text"/></div>

            <div class="label">Perkonnanimi:</div>
            <div class="input"><input id="lastName" name="lastName" value="" type="text"/></div>

            <div class="label">Hinne:</div>
            <div class="input">

                <input type="radio" name="grade" value="1">1
                <input type="radio" name="grade" value="2">2
                <input type="radio" name="grade" value="3">3
                <input type="radio" name="grade" value="4">4
                <input type="radio" name="grade" value="5">5
            </div>

            <div class="br"></div>

            <div class="label"></div>
            <div class="input button2">
                <input name="submitButton" type="submit" value="Salvesta">
            </div>

        </form>


    </main>

    <footer>
        ICD0007 Näidisrakendus

    </footer>

</div>

</body>
</html>