Add child

addChild.sol

pragma solidity ^0.8.15;

function addChild(uint256 parentTokenId, uint256 childTokenId)
    public
    virtual
{
    _requireMinted(parentTokenId);

    if (!_msgSender().isContract()) revert RMRKIsNotContract();

    Child memory child = Child({
        contractAddress: _msgSender(),
        tokenId: childTokenId
    });

    uint256 length = pendingChildrenOf(parentTokenId).length;

    if (length < 128) {
        _childIsInPending[child.contractAddress][child.tokenId] = 1; // We use 1 as true
        _pendingChildren[parentTokenId].push(child);
    } else {
        revert RMRKMaxPendingChildrenReached();
    }

    // Previous length matches the index for the new child
    emit ChildProposed(parentTokenId, _msgSender(), childTokenId, length);
}