There's no need to create an instance of such class for every call to
one of its methods. The balance is computed each time anyway, so it'll
always be up-to-date.
This keeps the `OrderBalance` abstraction but removes the old code now
that the feature is enabled for all users in all instances and there are
no bugs reported. It's become dead code.
This will let us branch by abstraction. All existing calls to
`#outstanding_balance` will go through `OrderBalance` hence, will
check the feature toggle.
Note that by default, `OrderBalance` will end up calling
`#old_outstanding_balance`. As the name states, that's exactly what
`#outstanding_balance` was so far. This means no consumers will see any
change in behavior. We just added on item in the call stack (sort of).
This model concerns helps us put together this related methods. Although
it doesn't provide any encapsulation yet, it makes a bit easier to
consider them all next time we need to change this implementation
somehow. It's a bit of an illusion but it feels like we are making this
God object model a bit smaller.
It also gives more room for documentation that will aid future devs.
Rails 5 introduced some breaking changes to these built-in methods, and the new versions no longer work correctly in relation to decrementing stock with VariantOverrides.
In the case where the variant has not been saved yet, we can use #new_record? here instead of #stock_items.empty?, to avoid an additional query. This can be called a vast number of times per request, in various N+1s. The other case where we need to return here is when a variant has been deleted, so #stock_items will be empty and #stock_item will be nil. Likewise, we can just check that with #deleted? and avoid #stock_items.empty?
variant.on_hand will not return infinity any longer if variant.on_demand is true. Clients of these methods will have to handle the combinations between on_hand and on_demand values
This ensures we can still use Order#shipment although Spree deprecates
it, while fixing a bug at the same time. The problem that was making the
test fail was on `Order#shipment` that Spree defines.
If the shipments association changes, `#shipment` returns stale data.
That is because the order object we might be using is still alive, and
so its @shipment ivar still holds an old shipment object (it's not nil)
and thus `@shipment ||= shipments.last` doesn't evaluate the right-hand
side of the expression.
Note that we need to `prepend` the evaluation of the concern (which it's
been rename) for our methods to take precedence over Spree ones. With
`include`, Spree's `#shipment` would still be picked up making the test
fail.
