Magento 2. What is the entity/class responsible for calculating the discount amount?

Question

• What is the entity/class responsible for calculating the discount amount?
• Where is this discount amount calculated?

Answer 1

It could be Magento\Quote\Model\Quote\Address\RulesApplier with its method applyRule() that calls setDiscountData() where the discount amount fields are setted.

$item->setDiscountAmount($discountData->getAmount());
$item->setBaseDiscountAmount($discountData->getBaseAmount());
$item->setOriginalDiscountAmount($discountData->getOriginalAmount());
$item->setBaseOriginalDiscountAmount($discountData->getBaseOriginalAmount());