Module 2: Ethereum & Smart Contracts

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

// A simple storage contract
contract SimpleStorage {
    // State variable to store a number
    uint256 public favoriteNumber;
    
    // Function to store a new number
    function store(uint256 _favoriteNumber) public {
        favoriteNumber = _favoriteNumber;
    }
    
    // Function to retrieve the stored number
    function retrieve() public view returns (uint256) {
        return favoriteNumber;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract EventExample {
    // Define an event
    event Transfer(
        address indexed from,    // indexed = searchable
        address indexed to,      // indexed = searchable
        uint256 amount          // not indexed
    );
    
    // Function that emits an event
    function transfer(address to, uint256 amount) public {
        // ... transfer logic here ...
        
        // Emit the event
        emit Transfer(msg.sender, to, amount);
    }
}

// Using ethers.js to listen for events
const contract = new ethers.Contract(address, abi, provider);

// Listen for Transfer events
contract.on("Transfer", (from, to, amount, event) => {
    console.log(`${from} sent ${amount} to ${to}`);
    // Update your UI here
});

// Query past events
const filter = contract.filters.Transfer(null, myAddress);
const events = await contract.queryFilter(filter);
console.log("Past transfers to me:", events);