//SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

import "../utils/BytesUtils.sol";
import "@ensdomains/buffer/contracts/Buffer.sol";

/// @dev RRUtils is a library that provides utilities for parsing DNS resource records.
library RRUtils {
    using BytesUtils for *;
    using Buffer for *;

    /// @dev Returns the number of bytes in the DNS name at 'offset' in 'self'.
    /// @param self The byte array to read a name from.
    /// @param offset The offset to start reading at.
    /// @return The length of the DNS name at 'offset', in bytes.
    function nameLength(
        bytes memory self,
        uint256 offset
    ) internal pure returns (uint256) {
        uint256 idx = offset;
        while (true) {
            assert(idx < self.length);
            uint256 labelLen = self.readUint8(idx);
            idx += labelLen + 1;
            if (labelLen == 0) {
                break;
            }
        }
        return idx - offset;
    }

    /// @dev Returns a DNS format name at the specified offset of self.
    /// @param self The byte array to read a name from.
    /// @param offset The offset to start reading at.
    /// @return ret The name.
    function readName(
        bytes memory self,
        uint256 offset
    ) internal pure returns (bytes memory ret) {
        uint256 len = nameLength(self, offset);
        return self.substring(offset, len);
    }

    /// @dev Returns the number of labels in the DNS name at 'offset' in 'self'.
    /// @param self The byte array to read a name from.
    /// @param offset The offset to start reading at.
    /// @return The number of labels in the DNS name at 'offset', in bytes.
    function labelCount(
        bytes memory self,
        uint256 offset
    ) internal pure returns (uint256) {
        uint256 count = 0;
        while (true) {
            assert(offset < self.length);
            uint256 labelLen = self.readUint8(offset);
            offset += labelLen + 1;
            if (labelLen == 0) {
                break;
            }
            count += 1;
        }
        return count;
    }

    uint256 constant RRSIG_TYPE = 0;
    uint256 constant RRSIG_ALGORITHM = 2;
    uint256 constant RRSIG_LABELS = 3;
    uint256 constant RRSIG_TTL = 4;
    uint256 constant RRSIG_EXPIRATION = 8;
    uint256 constant RRSIG_INCEPTION = 12;
    uint256 constant RRSIG_KEY_TAG = 16;
    uint256 constant RRSIG_SIGNER_NAME = 18;

    struct SignedSet {
        uint16 typeCovered;
        uint8 algorithm;
        uint8 labels;
        uint32 ttl;
        uint32 expiration;
        uint32 inception;
        uint16 keytag;
        bytes signerName;
        bytes data;
        bytes name;
    }

    function readSignedSet(
        bytes memory data
    ) internal pure returns (SignedSet memory self) {
        self.typeCovered = data.readUint16(RRSIG_TYPE);
        self.algorithm = data.readUint8(RRSIG_ALGORITHM);
        self.labels = data.readUint8(RRSIG_LABELS);
        self.ttl = data.readUint32(RRSIG_TTL);
        self.expiration = data.readUint32(RRSIG_EXPIRATION);
        self.inception = data.readUint32(RRSIG_INCEPTION);
        self.keytag = data.readUint16(RRSIG_KEY_TAG);
        self.signerName = readName(data, RRSIG_SIGNER_NAME);
        self.data = data.substring(
            RRSIG_SIGNER_NAME + self.signerName.length,
            data.length - RRSIG_SIGNER_NAME - self.signerName.length
        );
    }

    function rrs(
        SignedSet memory rrset
    ) internal pure returns (RRIterator memory) {
        return iterateRRs(rrset.data, 0);
    }

    /// @dev An iterator over resource records.
    struct RRIterator {
        bytes data;
        uint256 offset;
        uint16 dnstype;
        uint16 class;
        uint32 ttl;
        uint256 rdataOffset;
        uint256 nextOffset;
    }

    /// @dev Begins iterating over resource records.
    /// @param self The byte string to read from.
    /// @param offset The offset to start reading at.
    /// @return ret An iterator object.
    function iterateRRs(
        bytes memory self,
        uint256 offset
    ) internal pure returns (RRIterator memory ret) {
        ret.data = self;
        ret.nextOffset = offset;
        next(ret);
    }

    /// @dev Returns true iff there are more RRs to iterate.
    /// @param iter The iterator to check.
    /// @return True iff the iterator has finished.
    function done(RRIterator memory iter) internal pure returns (bool) {
        return iter.offset >= iter.data.length;
    }

    /// @dev Moves the iterator to the next resource record.
    /// @param iter The iterator to advance.
    function next(RRIterator memory iter) internal pure {
        iter.offset = iter.nextOffset;
        if (iter.offset >= iter.data.length) {
            return;
        }

        // Skip the name
        uint256 off = iter.offset + nameLength(iter.data, iter.offset);

        // Read type, class, and ttl
        iter.dnstype = iter.data.readUint16(off);
        off += 2;
        iter.class = iter.data.readUint16(off);
        off += 2;
        iter.ttl = iter.data.readUint32(off);
        off += 4;

        // Read the rdata
        uint256 rdataLength = iter.data.readUint16(off);
        off += 2;
        iter.rdataOffset = off;
        iter.nextOffset = off + rdataLength;
    }

    /// @dev Returns the name of the current record.
    /// @param iter The iterator.
    /// @return A new bytes object containing the owner name from the RR.
    function name(RRIterator memory iter) internal pure returns (bytes memory) {
        return
            iter.data.substring(
                iter.offset,
                nameLength(iter.data, iter.offset)
            );
    }

    /// @dev Returns the rdata portion of the current record.
    /// @param iter The iterator.
    /// @return A new bytes object containing the RR's RDATA.
    function rdata(
        RRIterator memory iter
    ) internal pure returns (bytes memory) {
        return
            iter.data.substring(
                iter.rdataOffset,
                iter.nextOffset - iter.rdataOffset
            );
    }

    uint256 constant DNSKEY_FLAGS = 0;
    uint256 constant DNSKEY_PROTOCOL = 2;
    uint256 constant DNSKEY_ALGORITHM = 3;
    uint256 constant DNSKEY_PUBKEY = 4;

    struct DNSKEY {
        uint16 flags;
        uint8 protocol;
        uint8 algorithm;
        bytes publicKey;
    }

    function readDNSKEY(
        bytes memory data,
        uint256 offset,
        uint256 length
    ) internal pure returns (DNSKEY memory self) {
        self.flags = data.readUint16(offset + DNSKEY_FLAGS);
        self.protocol = data.readUint8(offset + DNSKEY_PROTOCOL);
        self.algorithm = data.readUint8(offset + DNSKEY_ALGORITHM);
        self.publicKey = data.substring(
            offset + DNSKEY_PUBKEY,
            length - DNSKEY_PUBKEY
        );
    }

    uint256 constant DS_KEY_TAG = 0;
    uint256 constant DS_ALGORITHM = 2;
    uint256 constant DS_DIGEST_TYPE = 3;
    uint256 constant DS_DIGEST = 4;

    struct DS {
        uint16 keytag;
        uint8 algorithm;
        uint8 digestType;
        bytes digest;
    }

    function readDS(
        bytes memory data,
        uint256 offset,
        uint256 length
    ) internal pure returns (DS memory self) {
        self.keytag = data.readUint16(offset + DS_KEY_TAG);
        self.algorithm = data.readUint8(offset + DS_ALGORITHM);
        self.digestType = data.readUint8(offset + DS_DIGEST_TYPE);
        self.digest = data.substring(offset + DS_DIGEST, length - DS_DIGEST);
    }

    function isSubdomainOf(
        bytes memory self,
        bytes memory other
    ) internal pure returns (bool) {
        uint256 off = 0;
        uint256 counts = labelCount(self, 0);
        uint256 othercounts = labelCount(other, 0);

        while (counts > othercounts) {
            off = progress(self, off);
            counts--;
        }

        return self.equals(off, other, 0);
    }

    function compareNames(
        bytes memory self,
        bytes memory other
    ) internal pure returns (int256) {
        if (self.equals(other)) {
            return 0;
        }

        uint256 off;
        uint256 otheroff;
        uint256 prevoff;
        uint256 otherprevoff;
        uint256 counts = labelCount(self, 0);
        uint256 othercounts = labelCount(other, 0);

        // Keep removing labels from the front of the name until both names are equal length
        while (counts > othercounts) {
            prevoff = off;
            off = progress(self, off);
            counts--;
        }

        while (othercounts > counts) {
            otherprevoff = otheroff;
            otheroff = progress(other, otheroff);
            othercounts--;
        }

        // Compare the last nonequal labels to each other
        while (counts > 0 && !self.equals(off, other, otheroff)) {
            prevoff = off;
            off = progress(self, off);
            otherprevoff = otheroff;
            otheroff = progress(other, otheroff);
            counts -= 1;
        }

        if (off == 0) {
            return -1;
        }
        if (otheroff == 0) {
            return 1;
        }

        return
            self.compare(
                prevoff + 1,
                self.readUint8(prevoff),
                other,
                otherprevoff + 1,
                other.readUint8(otherprevoff)
            );
    }

    /// @dev Compares two serial numbers using RFC1982 serial number math.
    function serialNumberGte(
        uint32 i1,
        uint32 i2
    ) internal pure returns (bool) {
        unchecked {
            return int32(i1) - int32(i2) >= 0;
        }
    }

    function progress(
        bytes memory body,
        uint256 off
    ) internal pure returns (uint256) {
        return off + 1 + body.readUint8(off);
    }

    /// @dev Computes the keytag for a chunk of data.
    /// @param data The data to compute a keytag for.
    /// @return The computed key tag.
    function computeKeytag(bytes memory data) internal pure returns (uint16) {
        /* This function probably deserves some explanation.
         * The DNSSEC keytag function is a checksum that relies on summing up individual bytes
         * from the input string, with some mild bitshifting. Here's a Naive solidity implementation:
         *
         *     function computeKeytag(bytes memory data) internal pure returns (uint16) {
         *         uint ac;
         *         for (uint i = 0; i < data.length; i++) {
         *             ac += i & 1 == 0 ? uint16(data.readUint8(i)) << 8 : data.readUint8(i);
         *         }
         *         return uint16(ac + (ac >> 16));
         *     }
         *
         * The EVM, with its 256 bit words, is exceedingly inefficient at doing byte-by-byte operations;
         * the code above, on reasonable length inputs, consumes over 100k gas. But we can make the EVM's
         * large words work in our favour.
         *
         * The code below works by treating the input as a series of 256 bit words. It first masks out
         * even and odd bytes from each input word, adding them to two separate accumulators `ac1` and `ac2`.
         * The bytes are separated by empty bytes, so as long as no individual sum exceeds 2^16-1, we're
         * effectively summing 16 different numbers with each EVM ADD opcode.
         *
         * Once it's added up all the inputs, it has to add all the 16 bit values in `ac1` and `ac2` together.
         * It does this using the same trick - mask out every other value, shift to align them, add them together.
         * After the first addition on both accumulators, there's enough room to add the two accumulators together,
         * and the remaining sums can be done just on ac1.
         */
        unchecked {
            require(data.length <= 8192, "Long keys not permitted");
            uint256 ac1;
            uint256 ac2;
            for (uint256 i = 0; i < data.length + 31; i += 32) {
                uint256 word;
                assembly {
                    word := mload(add(add(data, 32), i))
                }
                if (i + 32 > data.length) {
                    uint256 unused = 256 - (data.length - i) * 8;
                    word = (word >> unused) << unused;
                }
                ac1 +=
                    (word &
                        0xFF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00) >>
                    8;
                ac2 += (word &
                    0x00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF00FF);
            }
            ac1 =
                (ac1 &
                    0x0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF) +
                ((ac1 &
                    0xFFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000) >>
                    16);
            ac2 =
                (ac2 &
                    0x0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF) +
                ((ac2 &
                    0xFFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000FFFF0000) >>
                    16);
            ac1 = (ac1 << 8) + ac2;
            ac1 =
                (ac1 &
                    0x00000000FFFFFFFF00000000FFFFFFFF00000000FFFFFFFF00000000FFFFFFFF) +
                ((ac1 &
                    0xFFFFFFFF00000000FFFFFFFF00000000FFFFFFFF00000000FFFFFFFF00000000) >>
                    32);
            ac1 =
                (ac1 &
                    0x0000000000000000FFFFFFFFFFFFFFFF0000000000000000FFFFFFFFFFFFFFFF) +
                ((ac1 &
                    0xFFFFFFFFFFFFFFFF0000000000000000FFFFFFFFFFFFFFFF0000000000000000) >>
                    64);
            ac1 =
                (ac1 &
                    0x00000000000000000000000000000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) +
                (ac1 >> 128);
            ac1 += (ac1 >> 16) & 0xFFFF;
            return uint16(ac1);
        }
    }
}