Fix dynamically applying discounts

[repl6669]

I came across a situation when discounts were not applied, because the calculate method was already called on cart. It is called during CartSession::use($cart) and also during CartSession::current(). This ended up with a state in DiscountManager, when the $discounts property was set to empty collection. Then the check in DiscountManager became true every time, because it only checks for null value and not empty collection.

After changing the check to count with empty collection as follows: ! $this->discounts || $this->discounts?->isEmpty()), there were multiple instances of the discounts added to $cart->discounts property. I mitigated this behavior by only adding discounts which are not already present in that property.

I also added a test which calls the $cart->calculate() method multiple times to make sure that discounts are added properly.

All tests are running green now, but this implementation is ofc open for discussion. Maybe there is a better solution.

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[glennjacobs]

This doesn't seem correct.

CartSession::use($cart) does NOT run the calculate method.

The only issue I can see, which probably needs fixing, is the Cart discounts property is not being reset when calculating, which can lead to the same discount being logged twice. I believe it probably needs adding here https://github.com/lunarphp/lunar/blob/0.5/packages/core/src/Pipelines/Cart/ApplyDiscounts.php#L18

E.g.

    public function handle(Cart $cart, Closure $next)
    {
        $cart->discounts = collect([]);  // <---------- this is new
        $cart->discountBreakdown = collect([]);

You probably need to update your test as follows

        // Calculate method called for the first time
        CartSession::use($cart)->calculate();

[glennjacobs]

See comments

[repl6669]

Hello @glennjacobs, I updated the test.

And yes, there were 2 problems.

1. Discounts could not be applied after first calculate call on Cart.
2. Discounts were added to $cart->discounts multiple times.

Let me know if I should do some more changes. Thank you.

[ryanmitchell]

Sorry for spamming the comments, but I would love if if this could be merged for 0.6. The lack of a count()/empty() check on discounts is biting us at the moment so we have to manually add it.