channel.sol

pragma solidity 0.4.24;

contract stateChannel{
    uint blockPeriod;
    uint neededSignatures;
    
    struct participant{
        bool isNeeded;
        uint256 block;
    }
    mapping(address => participant) channel;
    bytes32 stateRoot;
    
    uint constant BLOCKWEEK = 3000; 
    string constant prefix = "\x19Ethereum Signed Message:\n32";
    
    function updateState(bytes32 newRoot, bytes memory signature) public {
        require(signature.length %65 == neededSignatures);
        for(uint i=0; i < signature.length; i += 65){
            bytes32 r;
            bytes32 s;
            uint8 v;
            
            assembly{
                let ptr := add(add(signature,0x20), mul(0x20,i))
                r := mload(ptr)
                s := mload(add(ptr,0x20))
                v := byte(0,mload(add(ptr,0x40)))
            }
            bytes32 newHash = keccak256(abi.encodePacked(prefix,newRoot));
            address person = ecrecover(newHash, v,r,s);
            
            require(person != 0);
            require(channel[person].isNeeded);
            require(channel[person].block != block.number);
            channel[person].block = block.number;
        }
        stateRoot = newRoot;
    }
    
    function addPerson(address newPerson, bytes signature) public{
        
        require(signature.length %65 == neededSignatures);
        
        for(uint i=0; i < signature.length; i += 65){
            bytes32 r;
            bytes32 s;
            uint8 v;
            
            assembly{
                let ptr := add(add(signature,0x20), mul(0x20,i))
                r := mload(ptr)
                s := mload(add(ptr,0x20))
                v := byte(0,mload(add(ptr,0x40)))
            }
            bytes32 newHash = keccak256(abi.encodePacked(prefix,keccak256(newPerson)));
            address person = ecrecover(newHash, v,r,s);
            require(person != 0);
            require(channel[person].isNeeded);
            require(channel[person].block != block.number);
            channel[person].block = block.number;
        }
        
        neededSignatures++;
        channel[newPerson] = participant(true, block.number);
    }
    
    function removePerson(address person) public {
        require(channel[person].block < block.number - BLOCKWEEK && channel[person].block != 0);
        channel[person].isNeeded = false;
        neededSignatures--;
    }
    
    function updateMe() external{
        channel[msg.sender].block = block.number;
    }
    
    constructor(bytes32 channelHash, address[] participants){
        stateRoot = channelHash;
        channel[msg.sender] = participant(true, block.number);
        for(uint i =0; i<participants.length; i++){
            channel[participants[i]] = participant(true, block.number);
        }
    }
}