In which file in woocommerce is an order formed?

Question

Web development

The task is to implement wholesale prices without using the plugin. Prices do not fit the formula, they are formed arbitrarily.
It is necessary to set a wholesale price in a variable product for each variation, the wholesale price depends on the number of purchased products.
The plan is as follows: add fields for entering the quantity and entering the wholesale price for each variation, then change the price in the basket and design files through the condition. But I don’t know how to substitute my values ​​​​at the time of the order formation (In the admin panel and in the mail, data is needed taking into account the wholesale).
How can this be done correctly and safely, and in what file is the order generated?
PS If the solution is potentially crooked - tell me in which direction to move.