PHP Loan Request Project

Your brief

Write the rule and its tests before adding a form or database. This model is deliberately single-process and has no durable storage, so it cannot coordinate real concurrent borrowers. Returning a boolean separates a normal capacity rejection from an invalid-input exception. A later database implementation should preserve the observable contract through an authorised transactional operation rather than sharing this object between web requests.

Run it locally

Run this complete source locally with PHP 8.2 or newer. Save it using the filename shown and run the command below. PHP is not currently available in Bhylu’s browser playground. Apache and MySQL are not needed for an ordinary CLI example.

php -l loan-project.php
php loan-project.php

Download this source as a local PHP lab file. Keep lab files separate from the Bhylu project and production data.

Worked solution

<?php
declare(strict_types=1);

class LendingDesk {
    public function __construct(private int $available) { if ($available<0) throw new InvalidArgumentException("Negative stock"); }
    public function request(int $count): bool {
        if ($count<=0) throw new InvalidArgumentException("Positive request required");
        if ($count>$this->available) return false;
        $this->available-=$count; return true;
    }
    public function remaining(): int { return $this->available; }
}
$desk = new LendingDesk(6);
if (!$desk->request(4)) throw new RuntimeException("First request failed");
if ($desk->request(3)) throw new RuntimeException("Overdraw accepted");
if ($desk->remaining()!==2) throw new RuntimeException("Rejection changed stock");
echo "Reservation contract passed; 2 remain\n";

Reservation contract passed; 2 remain

Extend and test

Add returnUnits with a capacity invariant and test repeated or invalid returns.