pragma solidity ^0.8.4;

import "../dnssec-oracle/DNSSEC.sol";
import "../dnssec-oracle/BytesUtils.sol";
import "../dnssec-oracle/RRUtils.sol";
import "@ensdomains/buffer/contracts/Buffer.sol";

library DNSClaimChecker {

    using BytesUtils for bytes;
    using RRUtils for *;
    using Buffer for Buffer.buffer;

    uint16 constant CLASS_INET = 1;
    uint16 constant TYPE_TXT = 16;

    function getOwnerAddress(DNSSEC oracle, bytes memory name, bytes memory proof)
        internal
        view
        returns (address, bool)
    {
        // Add "_ens." to the front of the name.
        Buffer.buffer memory buf;
        buf.init(name.length + 5);
        buf.append("\x04_ens");
        buf.append(name);
        bytes20 hash;
        uint32 expiration;
        // Check the provided TXT record has been validated by the oracle
        (, expiration, hash) = oracle.rrdata(TYPE_TXT, buf.buf);
        if (hash == bytes20(0) && proof.length == 0) return (address(0x0), false);

        require(hash == bytes20(keccak256(proof)));

        for (RRUtils.RRIterator memory iter = proof.iterateRRs(0); !iter.done(); iter.next()) {
            require(RRUtils.serialNumberGte(expiration + iter.ttl, uint32(block.timestamp)), "DNS record is stale; refresh or delete it before proceeding.");

            bool found;
            address addr;
            (addr, found) = parseRR(proof, iter.rdataOffset);
            if (found) {
                return (addr, true);
            }
        }

        return (address(0x0), false);
    }

    function parseRR(bytes memory rdata, uint idx) internal pure returns (address, bool) {
        while (idx < rdata.length) {
            uint len = rdata.readUint8(idx); idx += 1;

            bool found;
            address addr;
            (addr, found) = parseString(rdata, idx, len);

            if (found) return (addr, true);
            idx += len;
        }

        return (address(0x0), false);
    }

    function parseString(bytes memory str, uint idx, uint len) internal pure returns (address, bool) {
        // TODO: More robust parsing that handles whitespace and multiple key/value pairs
        if (str.readUint32(idx) != 0x613d3078) return (address(0x0), false); // 0x613d3078 == 'a=0x'
        if (len < 44) return (address(0x0), false);
        return hexToAddress(str, idx + 4);
    }

    function hexToAddress(bytes memory str, uint idx) internal pure returns (address, bool) {
        if (str.length - idx < 40) return (address(0x0), false);
        uint ret = 0;
        for (uint i = idx; i < idx + 40; i++) {
            ret <<= 4;
            uint x = str.readUint8(i);
            if (x >= 48 && x < 58) {
                ret |= x - 48;
            } else if (x >= 65 && x < 71) {
                ret |= x - 55;
            } else if (x >= 97 && x < 103) {
                ret |= x - 87;
            } else {
                return (address(0x0), false);
            }
        }
        return (address(uint160(ret)), true);
    }
}