Aggregation

pragma solidity ^0.8.6;

import "@openzeppelin/contracts/access/Ownable.sol";
import "./GHGNFT.sol";
import "./GHGERC20.sol";
import "./GHGTOKEN.sol";

contract GHGAggregation is Ownable {

    GHGToken ghgToken;
    GHGERC20 ghgSavings;
    GHGERC20 ghgEmissions;
    GHGNFT ghgCertificates;

    uint256 public savings=0;
    uint256 public emissions=0;
    uint256 public cntNFTs=0;
    uint256 public cntAggregations=0;

    mapping (uint256 => uint256) public idToNft;
    mapping (uint256 => address) public adToNft;

    mapping (address => uint256) public approvedContributors;

    constructor(GHGToken _ghgToken) {
        ghgToken = _ghgToken;
        ghgSavings = _ghgToken.ghgSavings();
        ghgEmissions = _ghgToken.ghgEmissions();
        ghgCertificates = _ghgToken.ghgCertificates();
    }

    function approveContributor(address _contributor) public onlyOwner {
        approvedContributors[_contributor] = 1;
    }

    function declineContributor(address _contributor) public onlyOwner {
        approvedContributors[_contributor] = 0;
    }
   
    function addNFT(uint256 _tokenId) public {
        if ((msg.sender != owner()) && (approvedContributors[msg.sender] == 0)) {
            revert();
        } 
        if(ghgCertificates.ownerOf(_tokenId) == address(this)) {
            for(uint256 i=0;i<cntNFTs;i++) {
                if(idToNft[i] == _tokenId) revert();
            }
            idToNft[cntNFTs] = _tokenId;   
            cntNFTs++;
           
            address hash = nftTokenHolder(_tokenId);
            savings += ghgSavings.balanceOf(hash);
            emissions += ghgEmissions.balanceOf(hash);
        } else {
            revert();
        }
    }

    function addAggregation(GHGAggregation _aggregation) onlyOwner public {
        if(_aggregation.owner() == address(this)) {
            for(uint256 i=0;i<cntAggregations;i++) {
                if(adToNft[i] == address(_aggregation)) revert();
            }
            adToNft[cntAggregations] = address(_aggregation);   
            cntAggregations++;
            savings += _aggregation.savings();
            emissions += _aggregation.emissions();
        } else {
            revert();
        }
    }

    function transferAggregation(address to,GHGAggregation _aggregation) onlyOwner public {
       if(_aggregation.owner() == address(this)) {
            bool found=false;
            for(uint256 i=0;i<cntAggregations;i++) {
                if(adToNft[i] ==  address(_aggregation)) {
                    adToNft[i]=address(0);
                    found=true;
                }
            }
            if(found) {
                 savings -= _aggregation.savings();
                 emissions -= _aggregation.emissions();
                 _aggregation.transferOwnership(to);
            } else {
                revert();
            }
        } else {
            revert();
        }
    }

    function transferNft(address to,uint256 _tokenId) onlyOwner public {
        if(ghgCertificates.ownerOf(_tokenId) == address(this)) {
            bool found=false;
            for(uint256 i=0;i<cntNFTs;i++) {
                if(idToNft[i] == _tokenId) {
                    idToNft[i]=0;
                    found=true;
                }
            }
            if(found) {
                address hash = nftTokenHolder(_tokenId);
                savings -= ghgSavings.balanceOf(hash);
                emissions -= ghgEmissions.balanceOf(hash);
                ghgCertificates.transferFrom(address(this),to,_tokenId);
            } else {
                revert();
            }
        } else {
            revert();
        }
    }

    function nftTokenHolder(uint256 _tokenId) public view returns (address) {
                string memory hash = ghgCertificates.tokenURI(_tokenId);
                 uint endIndex =99;
                 uint startIndex =57;

                 bytes memory strBytes = bytes(hash); 
                 bytes memory result = new bytes(endIndex-startIndex); 

                 for(uint j = startIndex; j < endIndex; j++) { 
                     result[j-startIndex] = strBytes[j]; 
                  } 
                address did = toAddress(string(result));
                return did;
    }

    function fromHexChar(uint8 c) public pure returns (uint8) {
        if (bytes1(c) >= bytes1('0') && bytes1(c) <= bytes1('9')) {
            return c - uint8(bytes1('0'));
        }
        if (bytes1(c) >= bytes1('a') && bytes1(c) <= bytes1('f')) {
            return 10 + c - uint8(bytes1('a'));
        }
        if (bytes1(c) >= bytes1('A') && bytes1(c) <= bytes1('F')) {
            return 10 + c - uint8(bytes1('A'));
        }
        return 0;
    }

    function hexStringToAddress(string memory s) public pure returns (bytes memory) {
        bytes memory ss = bytes(s);
        require(ss.length%2 == 0); // length must be even
        bytes memory r = new bytes(ss.length/2);
        for (uint i=0; i<ss.length/2; ++i) {
            r[i] = bytes1(fromHexChar(uint8(ss[2*i])) * 16 +
                        fromHexChar(uint8(ss[2*i+1])));
        }

        return r;

    }
    
    function toAddress(string memory s) public pure returns (address) {
        bytes memory _bytes = hexStringToAddress(s);
        require(_bytes.length >= 1 + 20, "toAddress_outOfBounds");
        address tempAddress;

        assembly {
            tempAddress := div(mload(add(add(_bytes, 0x20), 1)), 0x1000000000000000000000000)
        }

        return tempAddress;
    }
}