Layer 2 Scaling: Rollups, Sidechains and State Channels

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

// Simplified optimistic rollup bridge contract
contract OptimisticBridge {
    struct Transaction {
        address sender;
        address recipient;
        uint256 amount;
        uint256 nonce;
    }
    
    struct Batch {
        bytes32 root;
        uint256 timestamp;
        bool finalized;
    }
    
    mapping(uint256 => Batch) public batches;
    uint256 public challengePeriod = 7 days;
    uint256 public batchCount;
    
    event BatchSubmitted(uint256 indexed batchId, bytes32 root);
    event Challenge(uint256 indexed batchId, uint256 indexed txIndex);
    
    function submitBatch(bytes32 _root) external {
        batchCount++;
        batches[batchCount] = Batch(_root, block.timestamp, false);
        emit BatchSubmitted(batchCount, _root);
    }
    
    function finalizeBatch(uint256 _batchId) external {
        Batch storage batch = batches[_batchId];
        require(block.timestamp >= batch.timestamp + challengePeriod, "Challenge period active");
        require(!batch.finalized, "Already finalized");
        
        batch.finalized = true;
    }
    
    function challengeTransaction(uint256 _batchId, Transaction calldata _tx, bytes[] calldata _proof) external {
        // Verify Merkle proof and check if transaction is invalid
        // If valid challenge, reward challenger and revert batch
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

// Simplified zk-rollup verifier interface
interface IVerifier {
    function verifyProof(
        uint256[2] memory a,
        uint256[2][2] memory b,
        uint256[2] memory c,
        uint256[] memory input
    ) external view returns (bool);
}

contract ZKRollup {
    IVerifier public verifier;
    mapping(uint256 => bytes32) public stateRoots;
    uint256 public stateId;
    
    event StateUpdated(uint256 indexed stateId, bytes32 newRoot);
    
    constructor(address _verifier) {
        verifier = IVerifier(_verifier);
    }
    
    function updateState(
        bytes32 _newRoot,
        uint256[2] memory a,
        uint256[2][2] memory b,
        uint256[2] memory c
    ) external {
        uint256[] memory input = new uint256[](1);
        input[0] = uint256(_newRoot);
        
        require(
            verifier.verifyProof(a, b, c, input),
            "Invalid proof"
        );
        
        stateId++;
        stateRoots[stateId] = _newRoot;
        emit StateUpdated(stateId, _newRoot);
    }
}

const { ethers } = require("ethers");

// Simulating a Polygon sidechain bridge interaction
async function bridgeToSidechain() {
  const mainnetProvider = new ethers.JsonRpcProvider("https://mainnet.infura.io/v3/YOUR_KEY");
  const polygonProvider = new ethers.JsonRpcProvider("https://polygon-rpc.com");
  
  // Lock tokens on mainnet
  const tokenAddress = "0x...";
  const bridgeAddress = "0x...";
  
  const token = new ethers.Contract(tokenAddress, [
    "function approve(address spender, uint256 amount) returns (bool)",
    "function balanceOf(address) view returns (uint256)]
  ], mainnetProvider);
  
  const bridge = new ethers.Contract(bridgeAddress, [
    "function deposit(uint256 amount) external",
    "function withdraw(uint256 amount) external",
    "function getBalance(address) view returns (uint256)]
  ], mainnetProvider);
  
  // Check balance
  const balance = await token.balanceOf(process.env.USER_ADDRESS);
  console.log("Mainnet balance:", ethers.formatEther(balance));
  
  // Bridge takes ~20-30 minutes for Polygon
  console.log("Bridging to Polygon...");
  console.log("Expected time: 20-30 minutes");
  console.log("Cost: ~0.01 ETH on mainnet + minimal on Polygon");
  
  // Once bridged, interact on Polygon
  const maticBalance = await polygonProvider.getBalance(process.env.USER_ADDRESS);
  console.log("Polygon MATIC balance:", ethers.formatEther(maticBalance));
}

// Expected output:
// Mainnet balance: 10.0
// Bridging to Polygon...
// Expected time: 20-30 minutes
// Cost: ~0.01 ETH on mainnet + minimal on Polygon
// Polygon MATIC balance: 100.0

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

contract SimpleStateChannel {
    struct Channel {
        address alice;
        address bob;
        uint256 aliceBalance;
        uint256 bobBalance;
        uint256 nonce;
        uint256 timeout;
        bool closed;
    }
    
    mapping(bytes32 => Channel) public channels;
    
    event ChannelOpened(bytes32 indexed channelId, address alice, address bob);
    event ChannelClosed(bytes32 indexed channelId, uint256 aliceBalance, uint256 bobBalance);
    
    function openChannel(address _counterparty) external payable returns (bytes32) {
        require(msg.value > 0, "Must deposit ETH");
        
        bytes32 channelId = keccak256(abi.encodePacked(msg.sender, _counterparty, block.timestamp));
        
        channels[channelId] = Channel({
            alice: msg.sender,
            bob: _counterparty,
            aliceBalance: msg.value,
            bobBalance: 0,
            nonce: 0,
            timeout: block.timestamp + 1 days,
            closed: false
        });
        
        emit ChannelOpened(channelId, msg.sender, _counterparty);
        return channelId;
    }
    
    function closeChannel(bytes32 _channelId, uint256 _aliceBalance, uint256 _bobBalance, bytes memory _signature) external {
        Channel storage channel = channels[_channelId];
        require(!channel.closed, "Already closed");
        
        bytes32 message = keccak256(abi.encodePacked(_channelId, _aliceBalance, _bobBalance, channel.nonce));
        
        // Verify both parties signed
        address signer = recoverSigner(message, _signature);
        require(signer == channel.alice || signer == channel.bob, "Invalid signature");
        
        channel.closed = true;
        
        payable(channel.alice).transfer(_aliceBalance);
        payable(channel.bob).transfer(_bobBalance);
        
        emit ChannelClosed(_channelId, _aliceBalance, _bobBalance);
    }
}