Fix for OpenSea lazy minting bullshit

src/nft/helpers.ts

@@ -40,6 +40,24 @@ export const nftsFromOperations = (ops: Operation[]): ProtoNFT[] => {
       }) as ProtoNFT;
 
       if (nftOp.type === "NFT_IN") {
+        // Because of how OpenSea is working with its "lazy minting" paradigm
+        // they can send an event pretending that you sent x NFT to an address
+        // while you actually never received it in the first place.
+        //
+        // E.g.: You create an NFT on OpenSea and "lazy mint" 2 ERC1155.
+        // You will not actually receive anything, it's off-chain and no one can actually
+        // know that you own those 2 NFTs except OpenSea itselft.
+        // Then you decide to send those 2 NFTs to someone (kvn).
+        // OpenSea will then mint and transfer 2 NFTs to kvn and fire an even saying that
+        // you sent 2 NFts to kvn. But since you never "received" them first, you had 0 NFT
+        // and you sent 2, therefore you now have -2 NFTs.
+        //
+        // We prevent that by setting the minimum amount of an NFT to 0 when a new "IN" transaction
+        // is incoming for it.
+        if (nft.amount.isNegative()) {
+          nft.amount = new BigNumber(0);
+        }
+
         nft.amount = nft.amount.plus(nftOp.value);
       } else if (nftOp.type === "NFT_OUT") {
         nft.amount = nft.amount.minus(nftOp.value);