> For the complete documentation index, see [llms.txt](https://docs.symm.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.symm.io/contract-documentation/symmio-options-v0.2.1/helper-contracts/trade-nft.md).

# Trade NFT

An ERC-721 contract that represents trade ownership as a transferable NFT. Token IDs map 1:1 to trade IDs in the Symmio protocol. Transferring the NFT automatically updates trade ownership in the protocol, and vice versa.

### How It Works

**Token ID = Trade ID.** When an NFT is minted for trade 42, the token ID is 42. No auto-increment.

**NFTs are opt-in.** Not every trade gets an NFT. PartyA must explicitly mint one via the core protocol.

**Two transfer paths exist, kept in sync:**

1. **User moves the NFT** → `_beforeTokenTransfer` hook calls `symmio.transferTradeFromNFT()` to update the protocol.
2. **Protocol moves the NFT** → `transferTradeNFT()` sets a flag (`transferInitiatedInSymmio`) so the hook doesn't call back into the protocol, avoiding an infinite loop.

***

### Constructor

```solidity
constructor(address symmio_) ERC721("Trade Ownership NFT", "TRNFT")
```

Reverts with `InvalidSymmioAddress` if `symmio_` is `address(0)`.

***

### Functions

#### mintNFTForTrade()

```solidity
function mintNFTForTrade(address partyA, uint256 tradeId) external onlySymmio;
```

Mints token `tradeId` to `partyA`. Only the Symmio contract can call this.

The `_beforeTokenTransfer` hook fires but skips the sync logic because `from == address(0)` (mint).

**Event:** `TradeNFTMinted(partyA, tradeId)`

#### transferTradeNFT()

```solidity
function transferTradeNFT(address from, address to, uint256 tradeId) external onlySymmio;
```

Transfer trade ownership associated with NFT.

***

### Events

| Event                                                                                    | When                             |
| ---------------------------------------------------------------------------------------- | -------------------------------- |
| `TradeNFTMinted(address indexed owner, uint256 indexed tokenId)`                         | NFT minted                       |
| `TradeNFTTransferred(uint256 indexed tokenId, address indexed from, address indexed to)` | User-initiated NFT transfer only |


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