subscribe.php

<?php

use Symfony\Component\Mailer\Mailer;
use Symfony\Component\Mime\Email;

require_once 'helpers.php';
require_once 'functions.php';
require_once 'data.php';
require_once 'session.php';

$follow_id = filter_input(INPUT_GET, 'id');
$sql = 'SELECT id
FROM users
WHERE id = ?;';
$stmt = db_get_prepare_stmt($connection, $sql, [$follow_id]);
mysqli_stmt_execute($stmt);
$result = mysqli_stmt_get_result($stmt);

if (!$result) {
    header('Location: error.php?code=404');
    exit;
}

$follower_id = $user['user_id'];
$sql = 'SELECT *' .
    ' FROM subscribes' .
    ' WHERE follow_id = ? AND follower_id = ?;';
$stmt = db_get_prepare_stmt($connection, $sql, [$follow_id, $follower_id]);
mysqli_stmt_execute($stmt);
$result = mysqli_stmt_get_result($stmt);
$result = mysqli_fetch_assoc($result);

if (!$result) {
    $sql = 'INSERT INTO subscribes (follow_id, follower_id)' .
        ' VALUES (?, ?)';
    $stmt = mysqli_prepare($connection, $sql);
    mysqli_stmt_bind_param($stmt, 'ii', $follow_id, $follower_id);
    mysqli_stmt_execute($stmt);
    $this_user = get_user($connection, $follow_id);
    $email = new Email();
    $email->from($email_configuration['from']);
    $email->to($this_user['email']);
    $email->subject('У вас новый подписчик');
    $email->text(
        'Здравствуйте, ' . $this_user['login'] . '. На вас подписался новый пользователь ' . $user['user'] . '. Вот ссылка на его профиль:' . $email_configuration['host_info'] . '/users_profile.php?id=' . $user['user_id']
    );
    $mailer = new Mailer($transport);
    $mailer->send($email);

    header('Location: users_profile.php?id=' . $follow_id);
    exit;
}