This is a new type of NFT to enforce traders to payback royalties. It's written for TonTech challenge about new NFT Standard to solve the problem related to royalty.

In this new type, the item has a exclusive status, and if the item is traded outside of the collection, it will receive an non-exclusive status. Like when we lend our car, which is a non-fungible asset, to a friend, but we still legally own it even if our friend lends it to someone else. When we want to legally transfer its ownership, we have to pay the transfer fees. This transfer must be done by an authority trusted by the parties to the transaction.

In this case, our subject is an NFT item. The legal owner is the last payer of the royalty. The trusted authority is the NFT collection.

Non-exclusive NFT can accept a list of all previous owners as those who have access to manage. So, having a whitelist of owners from previous addresses is not only not harmful, but sometimes useful. For example, the owner does not have access to the recent wallet, but can still control item using their previus wallet.

The transfer must be done by Collection, the amount of royalty sent by the marketplace must be greater than the amount of royalty at mint's time. We can ask for royalties for all unofficial transfers or latest one and a penalty defined by the collection's royalty params.

To legally transfer ownership:

when ungranted_transfers = 0: the transaction must contain value more than royalty at mint's time (which I named compensation).

when ungranted_transfers > 0: the transaction must contain value more than the result of multiplying the number of transactions in compensation (ungranted_transfers * (compensation || roylty)).

let compensation: Int = max(self.royalty_params.compensation, (context().value - commonFees) / transfers);

let debt: Int = transfers * compensation;
let restAmount: Int = context().value - commonFees - debt;

// enforce pay to transfer
// require(restAmount > 0, "Insufficient amount sent");
// OR 
// Reduce debt
// do {
//    // send royalty to creator and reduce ungranted_transfers 
// } until (ungranted_transfers > 0)
// OR friendly, process owner request
if(restAmount > 0) {
    //send official transfer and verify item
} else {
    //send unofficial transfer and increase ungranted_transfers
}

Collection does not reject any transfer request, even if the amount of context value is not enough to pay royalty, but changes the number of unofficial transfers. Therefore, owners have the freedom to manage their NFT in any way they like.

Based on exclusive status, collections decide how to provide them with future service (Staking, etc). For example their item will be labeled as Unsupported By Collection in the collection explorer.

This is the main goal, Legal transfer transaction must be done by collection and not directly by the marketplace.

So, we can use the pressure lever to trade through collection and payback royalties:

Unverified item have a list of previous owners' addresses (except the creator) and accept transfer request from old owners. Therefore, trading this NFT is very risky.

To convert a destroyed/unsupported NFT to be a exclusive item in the collection: we can calculate the times of unofficial transfers and receive royalties based on that and the rules defined by the creator.

If you find this repo useful please consider supporting my efforts by sending some TONs the address:

UQCjdCk7p7YatNMNpjVND1vMp7HqnF28u2N49P-fPeB93GyG

I am very grateful for the advice and participation of my dear friend @ProgramCrafter

Be careful when using my code. As I said before, this is a test implementation of the challenge and is NOT a deliverable product. However, you can contact me for more details. @hitasp