动态导航与用户认证：基于PHP会话实现登录状态感知按钮

<?php
// 确保在任何HTML输出之前调用 session_start()
if (session_status() == PHP_SESSION_NONE) {
    session_start();
}

// 检查用户是否已登录
if (isset($_SESSION['user_id'])) {
    // 用户已登录
    // 假设在登录时将用户名也存储在会话中，或者可以根据 user_id 从数据库获取
    $username = $_SESSION['username'] ?? '我的资料'; // 如果会话中没有用户名，提供一个默认值
    $link_target = 'profile.php'; // 登录后跳转到个人资料页
    $button_text = htmlspecialchars($username); // 显示用户名，并进行HTML实体转义
} else {
    // 用户未登录
    $link_target = 'login.php'; // 未登录时跳转到登录页
    $button_text = '登入/注册';
}
?>

<a href="<?php echo $link_target; ?>" class="get-started-btn">
    <?php echo $button_text; ?>
</a>

<?php
// ... 数据库连接 ...
$db = mysqli_connect('localhost', 'root', '', 'hdhouse');

if (isset($_POST['register'])) {
    $username = $_POST['username'];
    $email = $_POST['email'];
    $password = $_POST['password']; // 原始密码

    $errors = [];

    // 数据验证
    if (empty($username)) { array_push($errors, "Username is Required!"); }
    if (empty($email)) { array_push($errors, "Email is Required!"); }
    if (empty($password)) { array_push($errors, "Password is Required!"); }
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) { array_push($errors, "Invalid email format"); }
    if (!isset($_POST['term_check'])) { array_push($errors, "Please check the terms & conditions!"); }

    // 检查邮箱是否已存在 (使用预处理语句)
    $stmt_check_email = mysqli_prepare($db, "SELECT email FROM user WHERE email = ? LIMIT 1");
    mysqli_stmt_bind_param($stmt_check_email, "s", $email);
    mysqli_stmt_execute($stmt_check_email);
    mysqli_stmt_store_result($stmt_check_email);
    if (mysqli_stmt_num_rows($stmt_check_email) > 0) {
        array_push($errors, "Email already exists");
    }
    mysqli_stmt_close($stmt_check_email);

    // 如果没有错误，保存用户
    if (count($errors) == 0) {
        // 安全地哈希密码
        $hashed_password = password_hash($password, PASSWORD_DEFAULT);

        // 使用预处理语句插入用户数据
        $stmt_insert = mysqli_prepare($db, "INSERT INTO user (username, email, password) VALUES (?, ?, ?)");
        mysqli_stmt_bind_param($stmt_insert, "sss", $username, $email, $hashed_password);
        if (mysqli_stmt_execute($stmt_insert)) {
            // 注册成功后重定向
            $_SESSION['success'] = "Register Success!";
            header('location: login.php');
            exit();
        } else {
            array_push($errors, "Registration failed: " . mysqli_error($db));
        }
        mysqli_stmt_close($stmt_insert);
    }
}
?>

<?php
// 确保会话已启动
if (session_status() == PHP_SESSION_NONE) {
    session_start();
}
// ... 数据库连接 ...
$db = mysqli_connect('localhost', 'root', '', 'hdhouse');

if (isset($_POST['login'])) {
    $username_input = $_POST["username"];
    $password_input = $_POST["password"]; // 用户输入的密码

    $errors = [];

    // 数据验证
    if (empty($username_input)) { array_push($errors, "Username is Required!"); }
    if (empty($password_input)) { array_push($errors, "Password is Required!"); }

    if (count($errors) == 0) {
        // 使用预处理语句查询用户
        $stmt_login = mysqli_prepare($db, "SELECT user_id, username, password FROM user WHERE username = ?");
        mysqli_stmt_bind_param($stmt_login, "s", $username_input);
        mysqli_stmt_execute($stmt_login);
        $result = mysqli_stmt_get_result($stmt_login);
        $user = mysqli_fetch_assoc($result);
        mysqli_stmt_close($stmt_login);

        if ($user) {
            // 验证哈希密码
            if (password_verify($password_input, $user['password'])) {
                // 登录成功，设置会话变量
                $_SESSION["user_id"] = $user['user_id'];
                $_SESSION["username"] = $user['username']; // 将用户名也存入会话
                session_regenerate_id(true); // 重新生成会话ID，防止会话固定攻击
                header('location: 主页.php'); // 重定向到主页
                exit();
            } else {
                array_push($errors, "Wrong Username or Password!");
            }
        } else {
            array_push($errors, "Wrong Username or Password!");
        }
    }
}
?>