Closing the Auction

Once the auction's end time has elapsed, a transaction can be submitted to finalize the auction, distributing the token and the highest bid accordingly. This transaction needs to do the following:

• Spend the UTxO that contains the token being auctioned.
• If no bids were placed (which can be determined by examining the datum attached to the UTxO), the token should be returned to the seller's address.
• If at least one bid was placed, the token should be transferred to the highest bidder's address, and the highest bid amount should be sent to the seller's address.
• Set a validity interval that starts no earlier than the auction's end time.

The off-chain code for building and submitting this transaction will be very similar to the code for the bidding transactions, so the details are left as an exercise.

Illustration of this transaction: