新增需求：管理员添加留言后通知特定用户

我在这篇博客留言提醒自己增加这个需求：https://heybran.tech/node-js-testing-notes/#comment-54，在此记录一下实现的代码。查看了WordPress关于留言表单的源码：https://github.com/WordPress/wordpress-develop/blob/6.6.2/src/wp-includes/comment-template.php#L2784，我可以在comment_form_field_comment这个filter上面添加一个回调函数。

add_filter('comment_form_field_comment', function ($comment_field) {
	if (!current_user_can('manage_options')) {
		return $comment_field;
	}

	$notify_users_field = sprintf(
		'<p class="comment-form-notify-users">%s %s</p>',
		sprintf(
			'<label for="notify-users">%s</label>',
			__('通知用户')
		),
		'<input id="notify-users" name="notify-users" type="email" size="30" maxlength="100" placeholder="邮件地址用英文逗号隔开" />'
	);

	return $comment_field . $notify_users_field;
});

代码部署后前端效果 （不过这个输入框仅管理员可见）：

增加了一个邮件输入框来添加想要通知的邮箱，单独这个还不行，还需要监听这个comment_post事件。

add_action('comment_post', function ($comment_ID) {
	$comment = get_comment($comment_ID);

	// Only proceed if the current user is an admin and if the notify-users field is set
	if (current_user_can('manage_options') && !empty($_POST['notify-users'])) {
		// Sanitize and split the emails by commas
		$emails = explode(',', sanitize_text_field($_POST['notify-users']));

		// Get the comment and post information.
		$post = get_post($comment->comment_post_ID);

		// Loop through each email, validate, and send the email.
		foreach ($emails as $email) {
			$email = trim($email); // Remove any surrounding whitespace.
			if (is_email($email)) { // Check if it's a valid email address.
				wp_mail(
					$email,
					sprintf(__('Brandon在他的文章留言中@到了您 - %s'), $post->post_title),
					sprintf(
						__("Brandon在文章中添加了以下留言并提及到您:\n\n%s\n\n点击访问文章: %s"),
						get_comment_text($comment_ID),
						get_permalink($post)
					)
				);
			}
		}
	}
});