N

@if ($course->discount_exists)
    <s class="courses-body__price_crossed">
        {{$course->price->price}}$
    </s>  
@endif
<span class="courses-body__price">
    {{$course->price->price_with_discount}}$
</span>

public function getPriceWithDisacountAttribute(){
    return $this->price - $this->discount;
}

$rows= file_get_contents("ваш файл.txt");
$rows = mb_split("\r\n",$rows);
$rows= array_values(array_filter($rows,function($e){return mb_split("\|",$e)[1] == "busfor";}));

$onlyUnique = true;//доставать только уникальные
$result = [];
for($i = 0; $i < 7 && count($rows) > 0;$i++){	
	$inx =rand(0,count($rows)-1);
	$result[] = $rows[$inx];
	if($onlyUnique)
		array_splice($rows,$inx,1);
}
var_dump($result);

Декомпозиция

Глянул на пэт-проект, который сейчас пишу - 5тыс строк + 1тыс тестов, и если честно, ощущение, что проект даже не начал ещё толком писать.

Конечно архитектура - это ключевой вопрос. Не бойтесь рефакторить код в пользу хорошей архитектуры.
Если надо будет выбрать одно - переписать неэффективный алгоритм или переделать структуру проекта, я всегда выберу второе. Плохая архитектура похоронит проект, а плохой алгоритм или плохую реализацию функционала всегда можно переделать потом пока совсем не прижмет.
Конечно также нужны тесты хотя бы на ключевые штуки.

Скажу банальщину, но когда начинаешь можно не предвидеть все нюансы архитектуры, особенно если проект выбивается из того что делал ранее.

PS хотел бы ещё важное добавить, архитектурными делами надо заниматься не наскоками. Тут как back-end <-> front-end, мне например сложно перескакивать с одного на другое в течение дня, большие задачи делаю только одно, или back или front.
С архитектурой также надо поступать. Потому, что сложно переключать мышление с глобальных абстракций на детали реализации.

Ясно же, не долбить запросами гугл, отправлять запросы через рандомное время и с разных ip с разными настройками. А как иначе-то? Неужели вы полагаете, что против гугля есть специальный простой и надёжный приемчик, а гугль такой «ну ладно, это же тот самый приёмчик…»

Самое главное не высунуть php-fpm порт наружу в интернет что бы никто не запустит на нем какой-нибудь зловред.

Если же порт торчит из докера и прикрыт с наружи файр-волом то занчит вы знаете что делаете и принимаете на себя управление рисками you know exactly what you are doing (and are willing to accept the extreme risk)

Ели же у Вас из докера в интернет торчит неважно кто рнр, база данных или еще какой-нибудь сервис - повертье желающих его взломать достаточно

Эту инфу нужно искать в отрыве от языка, это уровень операционной системы.
Один из ответов на SO:
What is Under the Hood in a Stream in Programming?
Upd. Еще есть пересекающаяся тема как http streaming,
я когда-то для себя шпаргалку писала (ссылка)

Заказ хранить однозначно в базе.
При первом входе пользователю кидается кука. Не важно зарегистрирован или нет. И обязательно дайте какой нибудь идентификатор, который можно ввести на другом устройстве.
В итоге получаем 4 кейса.

1. аноним (без регистрации) - просто оформляет заказ, желательно, сохранить его данные и при последующем заказе подтянуть их что бы не заполнял снова, ну и выдать сообщение мы рады что вы вернулись. Привязка по почте, телелефону или адресу
2. аноним (он зарегистрирован, но пока не вошел) - при оформлении нужно показать сообщение мол вы можете войти и заполнить все данные автоматом
3. уже вошел в систему - тут просто оплата
4. ввод номера заказа на другом устройстве, тут устанавливается кука и подтягиваются данные с сервера

В вашем случае https://oracleplsql.ru/mysql-function-find_in_set.html MySql (5.7) -
FIND_IN_SET( string, string_list )

Но если не менять особо структуры, я бы переписал на Json столбец, с ним работать приятнее.

1. Если пользователь зарегистрировался и вошел в кабинет, то хранить в базе данных.
   
2. Если пользователь не зарегистрирован, то хранить в localStorage или в IndexedDB, просто потому что куки и сессия может быстро протухнуть, а это очень сильно разочаровывает, когда ты накидал интересных вещей в корзину, а через некоторое время открыл сайт, а в корзине пусто.
   
3. Если пользователь незарегистрированным накидал в корзину товаров, то если он зарегистрируется, то сохранить корзину в базу данных.
   

//Null-коалесцентный оператор нужен когда переменная может быть не определена, дабы не делать проверку на isset
$bar = $foo ?? 'default';   //default
$bar = $foo ?: 'default';   // Undefined variable $foo

Это совсем разные вещи.

?? - это null coalescing operator
?: - это ternary operator с первым выражением, эквивалентным выражению в левой части оператора.

implode(', ', array_reverse(explode(', ', $str)))

explode, array_reverse, implode