[API][UI][Behat][Refactor] OriginalUnitPrice property on the OrderItem entity

[Rafikooo]

Q	A
Branch?	1.11
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	no
License	MIT

To increase immutability, at the moment of adding an item to the cart, we should save the original price to the originalUnitPrice of this order item.
Using saved originalUnitPrice instead of using the prices from ChannelPricing while processing cart each time.

[vvasiloi]

WDYT about adding a method on the Order model to get the items total based on original unit price?

Edit: it would also require additional methods on the order item to calculate it's total first, plus a property to store the result and methods to recalculate the total. Just like with the current units and items total.

[Rafikooo]

TBH I'm not sure about that field. I checked the master demo API endpoint
api/v2/shop/account/orders/{tokenValue}/payments/{paymentId}
and it seems that that field should not be included, but I had one and it broke the tests

[Rafikooo]

After consultation with @GSadee originalUnitPrice can be included in that response

[GSadee]

Suggested change

	if ($this->originalUnitPriceIsGreaterThanUnitPriceAndDiscountedUnitPrice($item)) {
	return $item->getOriginalUnitPrice();
	} elseif($this->originalUnitPriceIsNullAndUnitPriceIsGreaterThanDiscountedUnitPrice($item)) {
	return $item->getUnitPrice();
	}
	return null;
	}
	private function originalUnitPriceIsGreaterThanUnitPriceAndDiscountedUnitPrice(OrderItem $item): bool
	{
	return ($item->getOriginalUnitPrice() !== null && $item->getOriginalUnitPrice() > $item->getUnitPrice()) ||
	($item->getOriginalUnitPrice() !== null && $item->getOriginalUnitPrice() > $item->getDiscountedUnitPrice());
	}
	private function originalUnitPriceIsNullAndUnitPriceIsGreaterThanDiscountedUnitPrice(OrderItem $item): bool
	{
	return $item->getOriginalUnitPrice() === null && $item->getUnitPrice() > $item->getDiscountedUnitPrice();
	}
	if (
	$item->getOriginalUnitPrice() !== null &&
	($item->getOriginalUnitPrice() > $item->getUnitPrice()) || $item->getOriginalUnitPrice() > $item->getDiscountedUnitPrice())
	) {
	return $item->getOriginalUnitPrice();
	}
	if ($item->getOriginalUnitPrice() === null && $item->getUnitPrice() > $item->getDiscountedUnitPrice()) {
	return $item->getUnitPrice();
	}
	return null;
	}

[GSadee]

Thanks, Rafał! 🎉