How would you organize such a schema in Yii2?

Question

Yii

Hello guys! There was one difficulty in understanding the actions!
How would you organize such a scheme:
Let's say the user, in the modal window, checks the boxes for products, clicks buy. And after a while, he again ticks the goods and clicks buy. But if he suddenly forgot that he had already ordered some goods before, a modal window should pop up offering to combine orders, thereby removing duplicate ones and adding new ones.
Just words to do in the controller and in JS scripts.

Answer 1

just take it and do it.
in a modal window? do it in modal.
1) call the modal for the checkboxes.
2) Place an order. (we write to the database)
3) the user repeats step 1.
4) we make a request again (so that the person does not fall off. and in case of an error, we could call the manager and fix the problem). but if there are repetitions in the order, then we ask the person to check his order again.