NFT Marketplace

How it works?

This is a platform that enables users to register NFT collections, sell or buy NFTs, and make offers on non-listed items. Here's how the marketplace works:

1. Users can create their own NFT collections with the NFT contract.
2. Users can mint NFTs. They should provide metadata which will be stored in IPFS.
3. Users can register their NFT collections with the Marketplace by using the addCollection function. This allows the Marketplace to track and manage the collections. In the context of this Marketplace a collection is considered a single ERC721 contract.
4. Users who own NFTs, can add their NFTs to the Marketplace using the addItem function. They specify the collection ID and the token ID of the NFT they want to add. This ensures that only NFTs from registered collections can be added to the marketplace.
5. Sellers can list their NFTs for sale by using the listItem function. They provide the item ID and set the price for the listed item. Only NFTs that have been previously added to the marketplace can be listed for sale.
6. Buyers can purchase NFTs that are listed for sale by using the buyItem function. They specify the item ID of the NFT they want to buy and send the required payment. Upon successful purchase, the NFT is transferred from the seller to the buyer, and the seller receives the payment. A fee is also charged by the marketplace contract.
7. Buyers can make offers on non-listed items by using the placeOffer function. They provide the item ID and the price they are willing to pay for the NFT. Similar to listing, the item must have been previously added to the marketplace but not listed for sale!
8. Sellers have the option to accept offers placed by buyers using the acceptOffer function. They specify the item ID and the address of the offerer whose offer they want to accept.
9. Claiming Items: Once a seller accepts an offer, the buyer can claim the item using the claimItem function. This transfers the NFT from the seller to the buyer and initiates the payment to the seller.
10. The owner of the marketplace contract can withdraw the accumulated fees from the contract using the withdraw function. This allows the owner to collect the earnings generated from the marketplace operations.

User stories

• User: Account willing to register NFT collections, sell or buy NFT.
• Seller: User who can add and list his NFTs or accept offers for his non-listed items on the Marketplace.
• Buyer: User who can buy listed items or place offers for other users' non-listed items.
• Marketplace: Smart contract which handles operations like adding, listing, buying, etc.
• NFT: ERC721 Smart contract which is considered a collection in the context of this project. It allows users to mint NFTs.
• Item: Structure on the Marketplace that represents NFTs with price and other useful properies.
• Offer: Structure that represents offer for non-listed item.
• Owner: Owner of the contract. He can withdraw the accumulated money from the Marketplace contract.

Architecture diagram

NFTMarketplace

Function	Parameters	Visibility & Modifiers	Description
addCollection	IERC721 _nftCollection	external	User registers collection to the Marketplace
addItem	uint256 _collectionId, uitn256 _tokenId	external	The user adds NFT to the Marketplace. Only from registered collections!
listItem	uint256 _itemId, uint256 _price	external	Seller list NFT item for sale. Only if the item is added to the Marketplace!
buyItem	uint256 _itemId	external, payable	The buyer buys the listed item, transfers the NFT to the buyer, pays to the seller, pays fee to the contract. Only if the item is listed!
placeOffer	uint256 _itemId, uint256 _price	external	Buyer places offer for non-listed item. Only if the item is added to the Marketplace!
acceptOffer	uint256 _itemId, address offerer	external	The seller accepts a placed offer.
claimItem	uint256 _itemId	external, payable	The buyer claims his item if the NFT owner has accepted his offer. It transfers the NFT to the buyer and pays the seller.
withdraw	-	external, OnlyOwner	The owner withdraws the accumulated fee from the contract.

NFT

Function	Parameters	Visability & Modifiers	Description
mint	string memory _tokenURI	external, returns (uint256)	Mints NFT to the msg.sender and sets metadata URI

Useablity specifics

1. After executing listItem function the Marketplace should be allowed to spend the NFT via his approve function.
2. After executing acceptOffer function the Marketplace should be allowed to spend the NFT via his approve function.
3. Before minting NFT via mint function, Metadata should be provided and stored to IPFS, the produced hash is being set as NFT metadata URI.

Events

NFTMarketplace

Events	Action	Parameters
LogCollectionAdded	A Collection has been added to the Marketplace	uint256 id, IERC721 indexed nftCollection
LogItemAdded	An Item has been added to the Marketplace	uint256 id, IERC721 indexed nftContract, uint256 tokenId, address indexed owner
LogItemListed	An Item has been listed to the Marketplace	uint256 id, IERC721 indexed nftContract, uint256 tokenId, address indexed seller, uint256 price
LogItemSold	An Item has been sold	uint256 id, IERC721 indexed nftContract, uint256 tokenId, address indexed seller, address indexed buyer, uint256 price
LogOfferPlaced	An Offer has been placed	uint256 id, IERC721 indexed nftContract, uint256 tokenId, address indexed buyer, uint256 price
LogOfferAccepted	An Offer has been accepted	uint256 indexed id, address indexed offerer
LogItemClaimed	An Item has been claimed	uint256 indexed id, address indexed claimer

• NFTMarketplace: 0xf4351BA9Ca701Cf689442833CDA5F7FF18C2e00C
• NFT: 0x78C3dbea63df38C52CE863989E09EfA38aDb7679