Bridge.sol

pragma solidity 0.6.4;
pragma experimental ABIEncoderV2;

import "./helpers/SafeMath.sol";
import "./interfaces/IRelayer.sol";
import "./interfaces/IDepositHandler.sol";
import "./interfaces/IBridge.sol";

contract Bridge {
    using SafeMath for uint;

    uint8                    public _chainID;
    IRelayer                 public _relayerContract;
    uint256                  public _relayerThreshold;
    RelayerThresholdProposal public _currentRelayerThresholdProposal;
    uint256                  public _totalDepositProposals;

    enum Vote {No, Yes}
    enum RelayerThresholdProposalStatus {Inactive, Active}
    enum DepositProposalStatus {Inactive, Active, Passed, Transferred}

    struct DepositProposal {
        bytes32                  _dataHash;
        address[]                _yesVotes;
        address[]                _noVotes;
        DepositProposalStatus    _status;
    }

    struct RelayerThresholdProposal {
        uint256                        _proposedValue;
        mapping(address => bool)       _hasVoted;
        address[]                      _yesVotes;
        address[]                      _noVotes;
        RelayerThresholdProposalStatus _status;
    }

    // destinationChainID => number of deposits
    mapping(uint8 => uint256) public _depositCounts;
    // destinationChainID => depositNonce => bytes
    mapping(uint8 => mapping(uint256 => bytes)) public _depositRecords;
    // destinationChainID => depositNonce => depositProposal
    mapping(uint8 => mapping(uint256 => DepositProposal)) public _depositProposals;
    // destinationChainID => depositNonce => relayerAddress => bool
    mapping(uint8 => mapping(uint256 => mapping(address => bool))) public _hasVotedOnDepositProposal;

    event RelayerThresholdProposalCreated(uint indexed proposedValue);
    event RelayerThresholdProposalVote(Vote vote);
    event RelayerThresholdChanged(uint indexed newThreshold);
    event Deposit(
        uint8   indexed destinationChainID,
        address indexed originChainHandlerAddress,
        uint256 indexed depositNonce
    );
    event DepositProposalCreated(
        uint8   indexed originChainID,
        uint8   indexed destinationChainID,
        uint256 indexed depositNonce,
        bytes32         dataHash
    );
    event DepositProposalVote(
        uint8   indexed       originChainID,
        uint8   indexed       destinationChainID,
        uint256 indexed       depositNonce,
        DepositProposalStatus status
    );
    event DepositProposalFinalized(
        uint8   indexed originChainID,
        uint8   indexed destinationChainID,
        uint256 indexed depositNonce
    );
    event DepositProposalExecuted(
        uint8   indexed originChainID,
        uint8   indexed destinationChainID,
        uint256 indexed depositNonce
    );

    modifier _onlyRelayers() {
        IRelayer relayerContract = IRelayer(_relayerContract);
        require(relayerContract.isRelayer(msg.sender), "sender must be a relayer");
        _;
    }

    constructor (uint8 chainID, address relayerContract, uint initialRelayerThreshold) public {
        _chainID = chainID;
        _relayerContract = IRelayer(relayerContract);
        _relayerThreshold = initialRelayerThreshold;
    }

    function getCurrentRelayerThresholdProposal() public view returns (
        uint256, address[] memory, address[] memory, RelayerThresholdProposalStatus) {
        return (
            _currentRelayerThresholdProposal._proposedValue,
            _currentRelayerThresholdProposal._yesVotes,
            _currentRelayerThresholdProposal._noVotes,
            _currentRelayerThresholdProposal._status
        );
    }

    function getDepositProposal(
        uint8 destinationChainID,
        uint256 depositNonce
    ) public view returns (DepositProposal memory) {
        return _depositProposals[destinationChainID][depositNonce];
    }

    function deposit(
        uint8        destinationChainID,
        address      originChainHandlerAddress,
        bytes memory data
    ) public {
        uint256 depositNonce = ++_depositCounts[destinationChainID];
        _depositRecords[destinationChainID][depositNonce] = data;

        IDepositHandler depositHandler = IDepositHandler(originChainHandlerAddress);
        depositHandler.deposit(destinationChainID, depositNonce, msg.sender, data);

        emit Deposit(destinationChainID, originChainHandlerAddress, depositNonce);
    }

    function voteDepositProposal(
        uint8   originChainID,
        uint256 depositNonce,
        bytes32 dataHash
    ) public _onlyRelayers {
        DepositProposal storage depositProposal = _depositProposals[uint8(originChainID)][depositNonce];

        require(uint(depositProposal._status) <= 1, "proposal has already been passed or transferred");
        require(!_hasVotedOnDepositProposal[originChainID][depositNonce][msg.sender], "relayer has already voted on proposal");

        if (uint(depositProposal._status) == 0) {
            ++_totalDepositProposals;
            _depositProposals[originChainID][depositNonce] = DepositProposal({
                _dataHash: dataHash,
                _yesVotes: new address[](1),
                _noVotes: new address[](0),
                _status: DepositProposalStatus.Active
            });

            depositProposal._yesVotes[0] = msg.sender;
            emit DepositProposalCreated(originChainID, _chainID, depositNonce, dataHash);
        } else {
            depositProposal._yesVotes.push(msg.sender);
        }

        _hasVotedOnDepositProposal[originChainID][depositNonce][msg.sender] = true;
        emit DepositProposalVote(originChainID, _chainID, depositNonce, depositProposal._status);

        // If _depositThreshold is set to 1, then auto finalize
        // or if _relayerThreshold has been exceeded
        if (_relayerThreshold <= 1 || depositProposal._yesVotes.length >= _relayerThreshold) {
            depositProposal._status = DepositProposalStatus.Passed;
            emit DepositProposalFinalized(originChainID, _chainID, depositNonce);
        }
    }

    function executeDepositProposal(
        uint8        originChainID,
        uint256      depositNonce,
        address      destinationChainHandlerAddress,
        bytes memory data
    ) public {
        DepositProposal storage depositProposal = _depositProposals[uint8(originChainID)][depositNonce];

        require(depositProposal._status != DepositProposalStatus.Inactive, "proposal is not active");
        require(depositProposal._status == DepositProposalStatus.Passed, "proposal was not passed or has already been transferred");
        require(keccak256(abi.encodePacked(destinationChainHandlerAddress, data)) == depositProposal._dataHash,
            "provided data does not match proposal's data hash");

        IDepositHandler depositHandler = IDepositHandler(destinationChainHandlerAddress);
        depositHandler.executeDeposit(data);

        depositProposal._status = DepositProposalStatus.Transferred;
        emit DepositProposalExecuted(originChainID, _chainID, depositNonce);
    }

    function createRelayerThresholdProposal(uint proposedValue) public _onlyRelayers {
        require(_currentRelayerThresholdProposal._status == RelayerThresholdProposalStatus.Inactive, "a proposal is currently active");
        require(proposedValue <= _relayerContract.getTotalRelayers(), "proposed value cannot be greater than the total number of relayers");

        _currentRelayerThresholdProposal = RelayerThresholdProposal({
            _proposedValue: proposedValue,
            _yesVotes: new address[](1),
            _noVotes: new address[](0),
            _status: RelayerThresholdProposalStatus.Active
            });

        if (_relayerThreshold <= 1) {
            _relayerThreshold = _currentRelayerThresholdProposal._proposedValue;
            _currentRelayerThresholdProposal._status = RelayerThresholdProposalStatus.Inactive;
            emit RelayerThresholdChanged(proposedValue);
        }
        // Record vote
        _currentRelayerThresholdProposal._yesVotes[0] = msg.sender;
        _currentRelayerThresholdProposal._hasVoted[msg.sender] = true;
        emit RelayerThresholdProposalCreated(proposedValue);
    }

    function voteRelayerThresholdProposal(Vote vote) public _onlyRelayers {
        require(_currentRelayerThresholdProposal._status == RelayerThresholdProposalStatus.Active, "no proposal is currently active");
        require(!_currentRelayerThresholdProposal._hasVoted[msg.sender], "relayer has already voted");
        require(uint8(vote) <= 1, "vote out of the vote enum range");

        // Cast vote
        if (vote == Vote.Yes) {
            _currentRelayerThresholdProposal._yesVotes.push(msg.sender);
        } else {
            _currentRelayerThresholdProposal._noVotes.push(msg.sender);
        }

        _currentRelayerThresholdProposal._hasVoted[msg.sender] = true;
        emit RelayerThresholdProposalVote(vote);

        // Todo: Edge case if relayer threshold changes?
        // Todo: For a proposal to pass does the number of yes votes just need to be higher than the threshold, or does it also have to be greater than the number of no votes?
        if (_currentRelayerThresholdProposal._yesVotes.length >= _relayerThreshold) {
            _relayerThreshold = _currentRelayerThresholdProposal._proposedValue;
            _currentRelayerThresholdProposal._status = RelayerThresholdProposalStatus.Inactive;
            emit RelayerThresholdChanged(_currentRelayerThresholdProposal._proposedValue);
        } else if (_relayerContract.getTotalRelayers().sub(_currentRelayerThresholdProposal._noVotes.length) < _relayerThreshold) {
            _currentRelayerThresholdProposal._status = RelayerThresholdProposalStatus.Inactive;
        }
    }
}