To checkout only selected cartLines in a cart

[wychoong]

To be able to only checkout selected items from a cart

example

Describe the solution you'd like

• A clean api on the Cart manager to select the items, example Cart::checkoutOnly([ ...Purchasable ])
• discount/shipping/tax etc should reflect accordingly
• order created only consist of those selected items
• leftover items to be in the next cart

Describe alternatives you've considered
as suggested by @glennjacobs possible workaround would be to create a new cart with just those items in and send to the checkout.
there is a downside of this, if the user didn't actually finish off the checkout process, the system will left with multiple stale carts. also, need to handle how to get all items in the cart while only calculating the selected and display the info, by handling 2 carts?

Additional context
these are my findings on possible way to add this into core, which is very little minimal code change

--- a/packages/core/src/DiscountTypes/AbstractDiscountType.php
+++ b/packages/core/src/DiscountTypes/AbstractDiscountType.php
@@ -49,7 +49,7 @@ abstract class AbstractDiscountType implements DiscountTypeInterface
      */
     protected function getEligibleLines(Cart $cart): Collection
     {
-        return $cart->lines;
+        return $cart->lines->filter(fn ($line) => $line->meta->checkout ?? true);
     }
 
     /**
--- a/packages/core/src/DiscountTypes/AmountOff.php
+++ b/packages/core/src/DiscountTypes/AmountOff.php
@@ -133,7 +133,7 @@ class AmountOff extends AbstractDiscountType
         $brandIds = $this->discount->brands->pluck('id');
         $productIds = $this->discount->purchasableLimitations->map(fn ($limitation) => get_class($limitation->purchasable).'::'.$limitation->purchasable->id);
 
-        $lines = $cart->lines;
+        $lines = parent::getEligibleLines($cart);
 
         if ($collectionIds->count()) {
             $lines = $lines->filter(function ($line) use ($collectionIds) {
--- a/packages/core/src/Pipelines/Cart/Calculate.php
+++ b/packages/core/src/Pipelines/Cart/Calculate.php
@@ -15,10 +15,12 @@ class Calculate
      */
     public function handle(Cart $cart, Closure $next)
     {
-        $discountTotal = $cart->lines->sum('discountTotal.value');
+        $checkedLines = $cart->lines->filter(fn ($line) => $line->meta->checkout ?? true);
 
-        $subTotal = $cart->lines->sum('subTotal.value') - $discountTotal;
-        $total = $cart->lines->sum('total.value');
+        $discountTotal = $checkedLines->sum('discountTotal.value');
+
+        $subTotal = $checkedLines->sum('subTotal.value') - $discountTotal;
+        $total = $checkedLines->sum('total.value');
 
         // Get the shipping address
         if ($shippingAddress = $cart->shippingAddress) {

currently I'm adding checkout = false to meta using the existing updateLine method
and it works like this

Screen.Recording.2023-02-26.at.01.54.04.mov

next item to look into will be how to handle remaining items
in the demo, what I understand is the paid cart need to be CartSession::forget() manually by the dev, which is perfectly fine.
so the possible way will be

1. dev to create a new cart with none checkout cartLines
2. or in Lunar, during CreateOrder action, move none checkout cartLines into a new cart, store the new cart id as a meta in current cart's meta, and then have an api CartSession::UseRemainingItemsCart() to retrieve the cart or null