usecase.php

<?php

interface Entity {
}

class Book implements Entity {
}

// REPO
interface Repository {
    public function getAll() : array;
    public function getOne() : Entity;
    public function update(Entity $entity) : void;
    public function save() : bool;
}

interface UseCase {}

/*class MysqlRepository implements Repository {
    public function getAll() : array;
    public function getOne() : Entity;
    public function update(Entity $entity) : void;
    public function save() : bool;
}*/

/*class InMemoryRepository {
    public function getAll() : array;
    public function getOne() : Entity;
    public function update(Entity $entity) : void;
    public function save() : bool;
}*/

class MongoRepository implements Repository {
    public function getAll() : array {
        return [
            'data' => [["id" => 1, "name" => "lorem"], ["id" => 2, "name" => "ipsum"]]
        ];
    }

    public function getOne() : Entity {
        return new Book();
    }

    public function update(Entity $entity) : void {
        
    }

    public function save() : bool {
        return true;
    }
}

interface Service {
    public function notify() : bool;
}


// SERVICE
class EmailService implements Service {
    public function notify() : bool {
        // send email, do logic business related to email
        return true;
    }
}

class BookUseCase implements UseCase {
    public function __construct(Repository $repo, Service $service) {
        $this->repo = $repo;
        $this->service = $service;
    }

    // POST /book
    public function createBookAndNotify() {
        $book = $_POST["foo"];
        $this->repo->getOne($book);

        // do something

        // Notify store, etc
        $this->service->notify();
    }

    public function getAllBooks() {
        return $this->repo->getAll();
    }
}

// index.php CONTROLLER / http request begin here:
$ctl = (new class(){

    public function setUseCase(UseCase $usecase) {
        $this->useCase = $usecase;
    }

    public function postBooks() {
        $this->useCase->createBookAndNotify();

        header('Content-type: application/json');
        echo json_encode($this->useCase->getAllBooks());
    }

    public function getBooks() {
        header('Content-type: application/json');
        echo json_encode($this->useCase->getAllBooks());
    }
});

$useCase = new BookUseCase(new MongoRepository(), new EmailService());
$ctl->setUseCase($useCase);

//echo '<pre>';
//var_dump($_SERVER); exit;

$requestUri = $_SERVER['REQUEST_URI'];

switch($requestUri) {
    case '/books':
        switch ($_SERVER['REQUEST_METHOD']) {
            case 'GET':
                $ctl->getBooks();
                break;
            case 'POST':
                $ctl->postBooks();
                break;
        }
        break;
}