//SPDX-License-Identifier: MIT
pragma solidity >=0.8.4;

library BytesUtils {
    /*
    * @dev Returns the keccak-256 hash of a byte range.
    * @param self The byte string to hash.
    * @param offset The position to start hashing at.
    * @param len The number of bytes to hash.
    * @return The hash of the byte range.
    */
    function keccak(bytes memory self, uint offset, uint len) internal pure returns (bytes32 ret) {
        require(offset + len <= self.length);
        assembly {
            ret := keccak256(add(add(self, 32), offset), len)
        }
    }

    /**
     * @dev Returns the ENS namehash of a DNS-encoded name.
     * @param self The DNS-encoded name to hash.
     * @param offset The offset at which to start hashing.
     * @return The namehash of the name.
     */
    function namehash(bytes memory self, uint offset) internal pure returns(bytes32) {
        (bytes32 labelhash, uint newOffset) = readLabel(self, offset);
        if(labelhash == bytes32(0)) {
            require(offset == self.length - 1, "namehash: Junk at end of name");
            return bytes32(0);
        }
        return keccak256(abi.encodePacked(namehash(self, newOffset), labelhash));
    }
    
    /**
     * @dev Returns the keccak-256 hash of a DNS-encoded label, and the offset to the start of the next label.
     * @param self The byte string to read a label from.
     * @param idx The index to read a label at.
     * @return labelhash The hash of the label at the specified index, or 0 if it is the last label.
     * @return newIdx The index of the start of the next label.
     */
    function readLabel(bytes memory self, uint256 idx) internal pure returns (bytes32 labelhash, uint newIdx) {
        require(idx < self.length, "readLabel: Index out of bounds");
        uint len = uint(uint8(self[idx]));
        if(len > 0) {
            labelhash = keccak(self, idx + 1, len);
        } else {
            labelhash = bytes32(0);
        }
        newIdx = idx + len + 1;
    }
}