Selling gift card ... download activation codes

Hi, we sell gift cards to be redeemed on our client websites and wondering if it would be possible for the user to receive the gift card activation code as a download or in their email after the purchase? I added a product, set it as a download product but can only upload 1 file. I would like to upload like 20 activation codes in a file or in a form with maybe possible expiry date and have the users receive the activation code after payment or after the order is set to complete. Each code can be use only once.

Please let me know if this can be done. I did some research but haven’t found anything.

Thank you for your time and help. If it’s something that needs to be programmed, who would you recommend?