Polygon Amoy Smart Contracts Architecture

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/metatx/ERC2771Context.sol";

contract CircularChainCore is ERC721, ERC2771Context {
    enum LotState { Listed, EscrowLocked, Transferred, EPRMinted, Retired }

    struct MaterialLot {
        uint256 lotId;
        address seller;       // Informal Collector
        address buyer;        // Enterprise Smelter
        uint256 massKg;
        uint256 purityBps;    // e.g. 9850 = 98.50%
        uint256 carbonOffsetKg;
        string ipfsProofHash; // Pinata CID
        LotState state;
    }

    mapping(uint256 => MaterialLot) public lots;

    event LotCreated(uint256 indexed lotId, address indexed seller, uint256 massKg);
    event EscrowLocked(uint256 indexed lotId, address indexed buyer);
    event OwnershipTransferred(uint256 indexed lotId, address indexed newOwner);

    constructor(address trustedForwarder) 
        ERC721("CircularChain Material Asset", "CCMAT")
        ERC2771Context(trustedForwarder) {}

    function listMaterial(
        uint256 massKg,
        uint256 purityBps,
        uint256 carbonOffsetKg,
        string calldata ipfsProofHash
    ) external returns (uint256 lotId) {
        lotId = uint256(keccak256(abi.encodePacked(_msgSender(), block.timestamp, massKg)));
        lots[lotId] = MaterialLot(lotId, _msgSender(), address(0), massKg, purityBps, carbonOffsetKg, ipfsProofHash, LotState.Listed);
        _safeMint(_msgSender(), lotId);
        emit LotCreated(lotId, _msgSender(), massKg);
    }
}