Implement the order summary totals

We need an OrderSummary service that will build the totals and supply them to the order total formatter for display.
The OrderSummary needs to inject the adjustment type manager to get the relevant weights.
Then in the buildTotals($order) method it calculates the subtotals the adjustment totals, the end total, returns all of that.

We summarize adjustments by adding together all of them which have the same type and source id. If the source id is NULL, we always leave that adjustment alone. Ideally we'd have $order->collectAdjustments() that gave you an array of all adjustments (order item + order ones).

(I guess the logic could live in the formatter itself but in our initial discussion having a service seemed cleaner.

We're close on this one. Primary tasks remaining are a unit test for the service and styling for the totals (something with two-columns and minimal styling).

@steveoliver, I'm testing and I have a problem. I add a tax using an order process service, like this: https://github.com/mglaman/commerce_demo/blob/master/src/OrderProcessor/.... Before patching with your code, this works correctly, the displayed order amount in checkout is adjusted and saved with the order, the adjustment is blobbed in the db for the order. After, my tax order process runs before your order total summary (i put a dsm in each), but $collected_adjustments = $order->collectAdjustments(); is empty, and in the db the order amount isn't adjusted. However, the adjustment, with the correct adjustment amount, DOES appear in commerce_order__adjustments. Any insight on this?

@steveoliver You are correct, I didn't define a "tax" adjustment type in a module yml file, to match the type I was creating in the OrderProcessor. Now that I have done that, it works. Thanks!

Wrapping this up.

Boom!

The change from using @steveoliver's pull request as a patch to this commit in the lastest 2.x-dev has caused the rendering of my Tax order adjustment to break.

It throws an error in commerce/modules/price/src/TwigExtension/PriceTwigExtension.php, InvalidArgumentException, because param price is null.

However, the summary DOES total the price with tax correctly (if I insert "return null" before throw new \InvalidArgumentException so I can see the page load).

Subtotal $1,815.00
Sales tax << where the problem is
Total $1,964.74

@ransomweaver
One of my changes was tweaking the output format of the totals.
You might have a custom template that's still using the old structure / variable names?

#21 works great, thanks @steveoliver

I wanted to rename amount to total, but the rename was incomplete. Now fixed. Sorry for the disturbance.