pragma solidity >=0.8.4;

import "./ENS.sol";

/// A registrar that allocates subdomains to the first person to claim them.
contract FIFSRegistrar {
    ENS ens;
    bytes32 rootNode;

    modifier only_owner(bytes32 label) {
        address currentOwner = ens.owner(
            keccak256(abi.encodePacked(rootNode, label))
        );
        require(currentOwner == address(0x0) || currentOwner == msg.sender);
        _;
    }

    /// Constructor.
    /// @param ensAddr The address of the ENS registry.
    /// @param node The node that this registrar administers.
    constructor(ENS ensAddr, bytes32 node) public {
        ens = ensAddr;
        rootNode = node;
    }

    /// Register a name, or change the owner of an existing registration.
    /// @param label The hash of the label to register.
    /// @param owner The address of the new owner.
    function register(bytes32 label, address owner) public only_owner(label) {
        ens.setSubnodeOwner(rootNode, label, owner);
    }
}