PiggyBank

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

/**
 * @title PiggyBank
 * @dev A simple piggy bank contract for depositing and withdrawing ETH
 */
contract PiggyBank {
    // Mapping to track each user's balance
    mapping(address => uint256) public balances;
    
    // Events to track deposits and withdrawals
    event Deposit(address indexed user, uint256 amount);
    event Withdrawal(address indexed user, uint256 amount);
    
    /**
     * @dev Function 1: Deposit ETH into your piggy bank
     */
    function deposit() public payable {
        require(msg.value > 0, "Must send some ETH!");
        balances[msg.sender] += msg.value;
        emit Deposit(msg.sender, msg.value);
    }
    
    /**
     * @dev Function 2: Withdraw your ETH from the piggy bank
     * @param amount Amount to withdraw in wei
     */
    function withdraw(uint256 amount) public {
        require(balances[msg.sender] >= amount, "Insufficient balance!");
        require(amount > 0, "Amount must be greater than 0!");
        
        balances[msg.sender] -= amount;
        payable(msg.sender).transfer(amount);
        emit Withdrawal(msg.sender, amount);
    }
    
    /**
     * @dev Function 3: Check your balance
     * @return Your current balance in wei
     */
    function getMyBalance() public view returns (uint256) {
        return balances[msg.sender];
    }
    
    /**
     * @dev Function 4: Say hello and show your balance
     * @return A friendly greeting with your balance
     */
    function sayHello() public view returns (string memory) {
        uint256 balance = balances[msg.sender];
        
        if (balance == 0) {
            return "Hello! Your piggy bank is empty. Time to save some ETH!";
        } else if (balance < 0.01 ether) {
            return "Hello! You're just getting started. Keep saving!";
        } else if (balance < 0.1 ether) {
            return "Hello! Nice savings! You're doing great!";
        } else {
            return "Hello! Wow! You're a crypto saver superstar!";
        }
    }
    
    /**
     * @dev Get the total contract balance
     */
    function getTotalContractBalance() public view returns (uint256) {
        return address(this).balance;
    }
    
    /**
     * @dev Fallback function to receive ETH
     */
    receive() external payable {
        deposit();
    }
}