hif - Highest in first out

I need a formaula - that works somewhat like FIFO -
like we have purchases of stocks on various dates- the prices var on each date of purchase -
so when i make sale - i want to deduct from the sale price the purchase price that has the heighest value in order to minimise my profits and ultimately the Tax.
now when we make next sale - we will check that how much units are deducted from the highest priced purchased and how much units are there -so that we may dededuct units adn then goes to second highest and so on.

Purchases
Date Units price
1-jan-2020 2 3
2 jan-2020 3 2
3- jan -2020 4 5

Sales

Date Units Price
2 jan 2020 3 6

Now the formula shall (keeping the dates in mind) goes to 1 -jan purchase as it has the highest purchase price and then from the sale price deduct the purchase price and give us profit on that sale - but it will just deduct the amount of 2 units and the third one shallbe from the next highest (with dates order) and deduct the remaining from those units like in this case the 2nd jan products and price.
hope you understand