PHP Decode

<?php 
 
session_start(); 
 
if (isset($_SESSION['user'])) { 
    header('Location: index.php'); 
    exit(); 
} 
 
include_once 'db.php'; 
include_once 'header.php'; 
 
if (isset($_POST['email'])) { 
    $conn = db_connect(); 
 
    $email = $_POST['email']; 
     
    // check if the email is valid 
    if (!preg_match('/^[a-zA-Z0-9_\.\@]+$/', $email)) { 
        echo "<div class='alert alert-danger'>Invalid email</div>"; 
    } else { 
        
        // check if the user exists 
        $sql = "SELECT * FROM users WHERE email = '$email'"; 
        $result = $conn->query($sql); 
        if ($result->num_rows > 0) { 
            if (isset($_POST['password'])) { 
                // check password 
                $row = $result->fetch_assoc(); 
                if ($row['password'] === $_POST['password']) { 
                    $_SESSION['user'] = $row['id']; 
                    echo "<meta http-equiv='refresh' content='0;url=/'>"; 
                } else { 
                    echo "<div class='alert alert-danger'>Invalid password</div>"; 
                } 
            } else { 
                echo "<div class='alert alert-danger'>Email already registered</div>"; 
            } 
        } else { 
            if (isset($_POST['password'])) { 
                echo "<div class='alert alert-danger'>User not found, please register first</div>"; 
            } else { 
                // create a new user 
                $id = bin2hex(random_bytes(16)); 
                $password = bin2hex(random_bytes(8)); 
                 
                $sql = "INSERT INTO users (id, email, username, password) VALUES ('$id', '$email', ?, ?)"; 
                $stmt = $conn->prepare($sql); 
                $stmt->bind_param('ss', $_POST['username'] , $password); 
                 
                if (!$stmt->execute()) { 
                    echo "Error creating user"; 
                    $stmt->close(); 
                    $conn->close(); 
                    exit(); 
                }  
                 
                echo "<div class='alert alert-success'>User created! Your password is \"$password\"</div>"; 
                $stmt->close(); 
            } 
        }  
        $conn->close(); 
    } 
} 
 
?> 
 
<div class=container> 
    <div class="row align-items-start"> 
        <div class="col-6"> 
            <h3>Register</h3> 
            <form method="post" class="mt-4 mx-4"> 
                <input type="text" class="form-control my-2" name="username" placeholder="username" required> 
                <input type="text" class="form-control my-2" name="email" placeholder="email" minlength="5" required> 
                <input type="submit" class="btn btn-primary my-2 w-100" value="Register"> 
            </form> 
        </div> 
        <div class="col-6"> 
            <h3>Login</h3> 
            <form method="post" class="mt-4"> 
                <textarea type="text" class="form-control my-2" name="email" placeholder="email" required></textarea> 
                <input type="password" class="form-control my-2" name="password" placeholder="password" required> 
                <input type="submit" class="btn btn-primary my-2 w-100" value="Login"> 
            </form> 
        </div> 
    </div> 
</div>