Advanced Cross-Chain Staking Portal Solidity, JavaScript, Web3

Okay, let's craft an example program illustrating a simplified cross-chain staking portal using Solidity, JavaScript, and Web3.  This example focuses on the core concepts and omits advanced features like relayers, complex token bridges, and robust security audits for brevity and clarity.

**Scenario:**

*   **Chain A (Ethereum):** Holds the staking token (e.g., `StakeToken`) and a basic staking contract (`StakingContract`).
*   **Chain B (Hypothetical):** Where the rewards accrue and the user's stake is represented by a mirrored token (e.g., `MirrorToken`).
*   **Functionality:**
    *   User stakes `StakeToken` on Chain A.
    *   The contract on Chain A emits an event.
    *   (Manually) Simulate a cross-chain message indicating the stake.  In a real system, a relayer network would handle this.
    *   A contract on Chain B receives the message and mints `MirrorToken` to represent the stake.
    *   (Later) User initiates unstaking on Chain A.
    *   The contract on Chain A emits an event.
    *   (Manually) Simulate a cross-chain message indicating the unstake request.
    *   A contract on Chain B receives the message, burns `MirrorToken`, and unlocks the stake on Chain A (simulated).

**Solidity (Chain A - Ethereum): `StakingContract.sol`**

```solidity
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract StakingContract is Ownable {
    IERC20 public stakeToken;
    mapping(address => uint256) public stakedBalances;
    uint256 public totalStaked;

    event Staked(address indexed user, uint256 amount);
    event Unstaked(address indexed user, uint256 amount);
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);


    constructor(address _stakeTokenAddress) {
        stakeToken = IERC20(_stakeTokenAddress);
    }

    function stake(uint256 _amount) external {
        require(_amount > 0, "Amount must be greater than zero.");

        // Transfer tokens from user to contract
        require(stakeToken.transferFrom(msg.sender, address(this), _amount), "Transfer failed.");

        stakedBalances[msg.sender] += _amount;
        totalStaked += _amount;

        emit Staked(msg.sender, _amount);
    }

    function unstake(uint256 _amount) external {
        require(_amount > 0, "Amount must be greater than zero.");
        require(stakedBalances[msg.sender] >= _amount, "Insufficient balance.");

        // Update balances
        stakedBalances[msg.sender] -= _amount;
        totalStaked -= _amount;

        // Transfer tokens back to user
        require(stakeToken.transfer(msg.sender, _amount), "Transfer failed.");

        emit Unstaked(msg.sender, _amount);
    }

    function getStakedBalance(address _user) external view returns (uint256) {
        return stakedBalances[_user];
    }

    function getTotalStaked() external view returns (uint256) {
        return totalStaked;
    }
}
```

**Solidity (Chain B - Hypothetical): `MirrorTokenContract.sol`**

```solidity
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MirrorTokenContract is ERC20, Ownable {

    mapping(address => bool) public trustedSenders; // Contracts allowed to mint/burn. In a real system, this would be a more sophisticated permissioning system (e.g., roles, signatures, etc.)
    event MirrorTokenMinted(address indexed user, uint256 amount);
    event MirrorTokenBurned(address indexed user, uint256 amount);


    constructor(string memory _name, string memory _symbol) ERC20(_name, _symbol) {
    }

    function setTrustedSender(address _sender, bool _isTrusted) external onlyOwner {
        trustedSenders[_sender] = _isTrusted;
    }

    function mintMirrorToken(address _user, uint256 _amount) external {
        require(trustedSenders[msg.sender], "Unauthorized: Sender not trusted.");
        _mint(_user, _amount);
        emit MirrorTokenMinted(_user, _amount);
    }

    function burnMirrorToken(address _user, uint256 _amount) external {
        require(trustedSenders[msg.sender], "Unauthorized: Sender not trusted.");
        require(balanceOf(_user) >= _amount, "Insufficient MirrorToken balance");
        _burn(_user, _amount);
        emit MirrorTokenBurned(_user, _amount);
    }

}
```

**JavaScript (Web3 Interaction):  `script.js`**

```javascript
// Requires: Web3.js library (install with npm install web3)
// Assumes you have deployed the contracts to Ganache or a testnet.
// Replace with your actual contract addresses and ABI definitions.
const Web3 = require('web3');

// Ethereum (Chain A) Configuration
const chainAProvider = new Web3.providers.HttpProvider('http://127.0.0.1:7545'); // Replace with your Chain A RPC URL
const chainAWeb3 = new Web3(chainAProvider);

const stakingContractAddress = '0x...'; // Replace with StakingContract address
const stakeTokenAddress = '0x...'; // Replace with StakeToken address

// Chain B Configuration (Simulated)
const chainBProvider = new Web3.providers.HttpProvider('http://127.0.0.1:8545'); // Replace with your Chain B RPC URL (e.g., a different Ganache instance)
const chainBWeb3 = new Web3(chainBProvider);

const mirrorTokenContractAddress = '0x...'; // Replace with MirrorTokenContract address

// Contract ABIs (Replace with actual ABIs)
const stakingContractABI = [...]; // Add the ABI for StakingContract
const stakeTokenABI = [...]; // Add the ABI for StakeToken
const mirrorTokenContractABI = [...]; // Add the ABI for MirrorTokenContract

// Create Contract Instances
const stakingContract = new chainAWeb3.eth.Contract(stakingContractABI, stakingContractAddress);
const stakeToken = new chainAWeb3.eth.Contract(stakeTokenABI, stakeTokenAddress);
const mirrorTokenContract = new chainBWeb3.eth.Contract(mirrorTokenContractABI, mirrorTokenContractAddress);

// Example Account (Replace with your test accounts)
const userAccountA = '0x...'; // Replace with your Chain A account
const userAccountB = '0x...'; // Replace with your Chain B account, if needed

async function stakeAndMintMirrorToken(amount) {
    try {
        // 1. Approve the StakingContract to spend StakeToken on Chain A
        const approveTx = await stakeToken.methods.approve(stakingContractAddress, amount).send({ from: userAccountA });
        console.log('Approval transaction:', approveTx.transactionHash);

        // 2. Stake tokens on Chain A
        const stakeTx = await stakingContract.methods.stake(amount).send({ from: userAccountA });
        console.log('Stake transaction:', stakeTx.transactionHash);

        // 3. Simulate Cross-Chain Message (Relayer role) - IMPORTANT:  In a real system, a relayer would listen for the Staked event and forward the data to Chain B.
        console.log('Simulating cross-chain message...');
        const trustedSender = '0x...'; // Account with permission on Chain B to mint mirror tokens.

        const mintTx = await mirrorTokenContract.methods.mintMirrorToken(userAccountA, amount).send({ from: trustedSender });

        console.log('Mint MirrorToken transaction:', mintTx.transactionHash);

    } catch (error) {
        console.error('Error:', error);
    }
}

async function unstakeAndBurnMirrorToken(amount) {
    try {
        //1.  Unstake Token on Chain A
        const unstakeTx = await stakingContract.methods.unstake(amount).send({ from: userAccountA });
        console.log('Unstake Transaction: ', unstakeTx.transactionHash);

        // 2. Simulate Cross-Chain Message (Relayer role)
        console.log('Simulating cross-chain message...');
        const trustedSender = '0x...'; // Account with permission on Chain B to burn mirror tokens.
        const burnTx = await mirrorTokenContract.methods.burnMirrorToken(userAccountA, amount).send({ from: trustedSender });

        console.log('Burn MirrorToken transaction:', burnTx.transactionHash);

    } catch (error) {
        console.error('Error: ', error);
    }
}

// Example Usage
async function main() {
    const stakeAmount = chainAWeb3.utils.toWei('1', 'ether'); // Stake 1 token
    await stakeAndMintMirrorToken(stakeAmount);

    const unstakeAmount = chainAWeb3.utils.toWei('0.5', 'ether'); // Unstake 0.5 token
    await unstakeAndBurnMirrorToken(unstakeAmount);
}

main();
```

**Explanation:**

1.  **Solidity Contracts:**
    *   `StakingContract.sol` (Chain A):
        *   Manages the staking of the `StakeToken` (ERC20).
        *   Uses `transferFrom` to receive tokens from users (requires approval).
        *   Emits `Staked` and `Unstaked` events.  These are crucial for triggering cross-chain actions.
    *   `MirrorTokenContract.sol` (Chain B):
        *   Creates a `MirrorToken` (ERC20) representing the stake on Chain A.
        *   Has `mintMirrorToken` and `burnMirrorToken` functions, which are only callable by a `trustedSender` (a contract authorized to mint/burn).  This is where a relayer would act on Chain B.

2.  **JavaScript (Web3):**
    *   **Configuration:** Sets up Web3 providers for both Chain A and Chain B.  You'll need to point these to your blockchain nodes (e.g., Ganache).  **Important:** Use different ports for Chain A and Chain B Ganache instances if you are using Ganache.
    *   **Contract Instances:** Creates JavaScript objects representing the deployed Solidity contracts, using their addresses and ABIs.
    *   **`stakeAndMintMirrorToken` function:**
        *   `approve`:  First, the user *must* approve the `StakingContract` to spend their `StakeToken` on Chain A.  This is a standard ERC20 requirement.
        *   `stake`:  The user calls the `stake` function on the `StakingContract` on Chain A.
        *   **Simulated Cross-Chain Message:**  This is the key part. In a real system, you'd have a *relayer network* listening for the `Staked` event emitted by the `StakingContract` on Chain A.  The relayer would then construct a transaction on Chain B to call the `mintMirrorToken` function of the `MirrorTokenContract`.  Here, we're just simulating that process.
        *   `mintMirrorToken`: Calls the `mintMirrorToken` function on the `MirrorTokenContract` on Chain B, minting the equivalent amount of `MirrorToken` to the user.
    *   **`unstakeAndBurnMirrorToken` function:**
        *   `unstake`: Calls the `unstake` function on the `StakingContract` on Chain A, returning the `StakeToken` to the user.
        *   **Simulated Cross-Chain Message:**  Again, simulating the relayer.
        *   `burnMirrorToken`: Calls the `burnMirrorToken` function on the `MirrorTokenContract` on Chain B, burning the `MirrorToken` from the user.

3.  **Important Notes:**

    *   **Relayers:** This example *completely skips* the relayer network.  Relayers are the crucial component that bridge the gap between chains.  They listen for events on one chain and execute transactions on another. Building a robust relayer network is a complex task. There are services like Chainlink CCIP and LayerZero that provide cross-chain messaging infrastructure.
    *   **Security:** This example is for demonstration purposes *only*.  It lacks essential security measures for a production environment. You'd need to implement proper access control, input validation, reentrancy protection, and perform thorough security audits.
    *   **Error Handling:**  The JavaScript code includes basic error handling (`try...catch`), but in a real application, you'd want more sophisticated error reporting and retry mechanisms.
    *   **Gas Costs:**  Cross-chain transactions can be expensive due to the gas costs on each chain and the fees charged by relayers.
    *   **Atomic Transactions:** Ensuring that actions on both chains happen atomically (either both succeed or both fail) is a major challenge in cross-chain development.  Solutions often involve complex protocols and trusted intermediaries.
    *   **Front-End:** This example doesn't include a front-end.  You'd need to build a user interface to allow users to interact with the contracts. The front-end would use Web3.js to connect to the user's wallet (e.g., MetaMask) and call the contract functions.
    *   **Chain IDs:**  Make sure that your Web3 providers are configured with the correct chain IDs for your target blockchains.

**To Run This Example:**

1.  **Set up Ganache:**  Start two Ganache instances (or use other local testnets) on different ports.
2.  **Deploy Contracts:** Deploy the `StakingContract` to Chain A and the `MirrorTokenContract` to Chain B.  Also deploy an ERC20 token to chain A and set it as the `stakeToken`. Make sure to deploy as the same account on both chains.
3.  **Update Addresses:**  Replace the placeholder addresses in `script.js` with the actual deployed contract addresses.  Also update the `userAccountA`, `userAccountB`, and `trustedSender` with the deployer account address.
4.  **Approve Spending:** Approve the `StakingContract` on Chain A to spend your `StakeToken`.  You can do this using a separate script or directly in the Ganache interface.
5.  **Run the Script:** Execute the `script.js` file using Node.js: `node script.js`

Remember that this is a highly simplified example. Building a real-world cross-chain application requires deep knowledge of blockchain technology, security best practices, and cross-chain communication protocols.