hardhat-simple-storage/contracts/FundMe.sol

// SPDX-License-Identifier: MIT
/*
    Get funds from users
    Withdraw funds
    Set a minimum funding value in USD
*/
/***** 1. Pragma *****/
pragma solidity ^0.8.0;

/***** 2. Import *****/
import "./PriceConverter.sol";
import "hardhat/console.sol";
// Save Gas by using constant, immutable for variables

/***** 3. Error Codes *****/
error FundMe__NotOwner();

/***** 4. Interfaces *****/

/***** 5. Libraries *****/

/***** 6. Contracts *****/
/**
 * @title A contract for crowd funding
 * @author hoelee
 * @notice This contract is to demo a sample funding contract
 * @dev This implements price feed as our library
 */
contract FundMe {
    /*
        Transaction Fields
            Nonce
            Gas Price
            Gas Limit - Max Gas that this TX can use
            To - Address
            Value - Amount of wei to send
            Data - What to send to the Address (Can Empty)
            v, r, s - components of TX signature
    */

    /***** 6.1 Type Declarations *****/
    using PriceConverter for uint256;
    uint256 public constant MINIMUM_USD = 50 * 1e18;
    address[] private s_funders;
    address private immutable i_owner; // immutable only can declare 1 time at contructor
    AggregatorV3Interface private s_priceFeed;

    /***** 6.2 State Variable *****/
    mapping(address => uint256) private s_addressToAmountFunded;

    /***** 6.3 Modifier *****/
    modifier onlyOwner() {
        // require(msg.sender == i_owner, "Sender is not owner!");
        if (msg.sender != i_owner) {
            revert FundMe__NotOwner();
        }
        _; // doing the rest of the code

        console.log("Log available via 'yarn hardhat test'");
    }

    /***** Function Orders:
     * Constructor
     * Receive
     * Fallback
     * External
     * Public Internal
     * Private
     * View / Pure
     *  *****/

    constructor(address s_priceFeedAddress) {
        i_owner = msg.sender;
        s_priceFeed = AggregatorV3Interface(s_priceFeedAddress);
    }

    // What happens if someone send this contract ETH without calling the fund function
    receive() external payable {
        // people send money / empty money into this contract
        fund();
    }

    fallback() external payable {
        // cannot identify which function to run
        fund();
    }

    /**
     * @notice Minimum sending USD50, Check Conversion In Real Time
     * @dev This implements price feed as our library
     */
    function fund() public payable {
        //require (msg.value >= 1e18, "Didn't send enough"); // 1e18 = 1 * 10 * 18 = 1000000000000000000
        require(
            msg.value.getConversionRate(s_priceFeed) >= MINIMUM_USD,
            "Didn't send enough"
        ); // Use error code is gas cheaper
        s_funders.push(msg.sender);
        s_addressToAmountFunded[msg.sender] = msg.value;
    }

    // Owner of this contract only can withdraw
    function withdraw() public onlyOwner {
        // Can use modifier to replace
        // require(msg.sender == owner, "Sender is not owner");

        /* starting index, eding index, step amount */
        for (
            uint256 funderIndex = 0;
            funderIndex < s_funders.length;
            funderIndex++
        ) {
            address funder = s_funders[funderIndex];
            s_addressToAmountFunded[funder] = 0;
        }
        // reset the array
        s_funders = new address[](0);

        /*
        // transfer - over 2300 gas will cause exception
        payable(msg.sender).transfer(address(this).balance);
        // send - over 2300 gas will not cause exception, only will return true or false
        bool sendSuccess = payable(msg.sender).send(address(this).balance);
        require(sendSuccess, "Send failed");
        */

        // call - lower level
        (bool callSuccess, ) = payable(msg.sender).call{
            value: address(this).balance
        }("");
        require(callSuccess, "Call failed");
    }

    function cheaperWithdraw() public onlyOwner {
        address[] memory funders = s_funders;
        for (
            uint256 funderIndex = 0;
            funderIndex < funders.length;
            funderIndex++
        ) {
            address funder = funders[funderIndex];
            s_addressToAmountFunded[funder] = 0;
        }
        // reset the array
        s_funders = new address[](0);

        (bool callSuccess, ) = i_owner.call{value: address(this).balance}("");
        require(callSuccess, "Call failed");
    }

    // private variable is gas cheaper
    function getOwner() public view returns (address) {
        return i_owner;
    }

    function getFunders(uint256 index) public view returns (address) {
        return s_funders[index];
    }

    function getAddressToAmountFunded(
        address funder
    ) public view returns (uint256) {
        return s_addressToAmountFunded[funder];
    }

    function getPriceFeed() public view returns (AggregatorV3Interface) {
        return s_priceFeed;
    }
}