Get the last trade

Hello,
In my datapack, I have a custom villager, with custom trades.
I would like to test the trades made by the players.
More precisely, I want to know what the player has just bought from this villagers to enable stock and bank management in the linked chests.
I have the “What a Deal!” advancement in “minecraft:advancement/adventure/trade” to allow me to launch a function once the trade has been completed.
i just have to detect what has been bought from the villager.
do you have a solution ?
Thanks