pragma solidity ^0.8.0;

contract Marketplace {
    uint256 internal currentKey = 1375566;
    struct Item {
        uint16 useless;
        uint256 keyId;
        bytes32 data;
    }

    mapping(uint256 => Item) public items;

    function addItem(bytes32 _data) public returns (Item memory) {
    currentKey += 174; 

        // Store the item
        items[currentKey] = Item({
            useless: 16,
            keyId: currentKey,
            data: _data
        });
    return items[currentKey];
    }

    function getItem(uint256 _keyId) public view returns (Item memory) {
        assert(items[_keyId].keyId == 0);
    }
}