Apply cart rule to products without other discount

Question

Scenario:
Add a new condition to the cart rules in the section "Apply the rule only to cart items matching the following conditions".
The condition should like this: "If Absolute discount amount is/greater/... {value here}".

Example:"Absolute discount amount is 0".
This means that the item should not be matched if it already has a discount.
Adding the new condition was fairly easy.
I added a plugin on Magento\SalesRule\Model\Rule\Condition\Product. afterLoadAttributeOptions

public function afterLoadAttributeOptions(\Magento\SalesRule\Model\Rule\Condition\Product $subject, \Magento\SalesRule\Model\Rule\Condition\Product $result)
{
    $attributes = $subject->getAttributeOption();
    $attributes['quote_item_absolute_discount'] = __('Absolute discount amount'); 
    asort($attributes);
    $subject->setAttributeOption($attributes);
    return $result;
}

This makes it appear in the backend and behave as it should

Now I tried to validate my new condition:
In the same class I have this around plugin

public function aroundValidate(Product $subject, callable $proceed, \Magento\Framework\Model\AbstractModel $model)
{
    if ($subject->getAttribute() === 'quote_item_absolute_discount') {             //if not checking on quote item, let the original method execute
        if ($model instanceof \Magento\Quote\Model\Quote\Item) {
            //set the value of the absolute discount to the product and let the original method validate it
            $model->getProduct()->setData('quote_item_absolute_discount', $model->getDiscountAmount());
        }
    }
    return $proceed($model);
}

I did this for other conditions and it works nicely.
But in this case, because the rules validation is a separate process from applying the rules, I always get 0 for $model->getDiscountAmount().
Even if there are other rules applied to the cart before my rule, the validation is done before applying all the other rules.
Any idea on how I can make this work?

Answer 1

I was wrong.
There is no separation between validate and apply rules.
\Magento\SalesRule\Model\RulesApplier::applyRules loops though all the rules (not actually all, they are filtered first based on status and start/end date).
If a rule is valid, then it applies it.
The problem in my case was caused by something else, that I overlooked.
in the same method mentioned above... if a rule is not matched for a configurable product, it is validated against the simple product added to the cart along with the configurable one.
And it my case it matched the simple product.
To solve it I changed the method aroundValidate shown in the question to:

public function aroundValidate(Product $subject, callable $proceed, \Magento\Framework\Model\AbstractModel $model)
{
    if ($subject->getAttribute() === 'quote_item_absolute_discount') {
        //if not checking on quote item, let the original method execute
        if ($model instanceof \Magento\Quote\Model\Quote\Item) {
            //set the value of the discount amount to the product and let the original method validate it
            $product = $model->getProduct();
            if (!$product->hasData('quote_item_absolute_discount')) {
                $model->getProduct()->setData('quote_item_absolute_discount', $model->getDiscountAmount());
            }
            $children = $model->getChildren();
            //make the child items aware of the discount amount.
            if (count($children)) {
                foreach ($children as $child) {
                    $product = $child->getProduct();
                    if (!$product->hasData('quote_item_absolute_discount')) {
                        $child->getProduct()->setData('quote_item_absolute_discount', $model->getDiscountAmount());
                    }
                }
            }
        }
    }
    return $proceed($model);
}

Looks like it's working now.