// SPDX-License-Identifier: MIT
// Author: https://github.com/jspruance

pragma solidity ^0.8.11;

contract VendingMachine {
    address public owner;
    mapping(address => uint256) public balances;

    constructor() {
        owner = msg.sender; // deployer of contract to be set = owner
        balances[address(this)] = 50; // initial bal (we need to start with something in it)
    }

    function getMachineBalance() public view returns (uint256) {
        return balances[address(this)];
    }

    // Let the owner restock the vending machine
    function restock(uint256 amount) public {
        require(msg.sender == owner, "Only the owner can restock.");
        balances[address(this)] += amount;
    }

    // Purchase donuts from the vending machine
    function purchase(uint256 amount) public payable {
        require(
            msg.value >= amount * 2 ether,
            "You must pay at least 2 ETH per donut"
        );
        require(
            balances[address(this)] >= amount,
            "Not enough donuts in stock to complete this purchase"
        );
        balances[address(this)] -= amount;
        balances[msg.sender] += amount;
    }
}