Solidity x Hardhat 101

hardhat.config.ts

import * as dotenv from "dotenv";

import { HardhatUserConfig, task } from "hardhat/config";
import "@nomiclabs/hardhat-etherscan";
import "@nomiclabs/hardhat-waffle";
import "@typechain/hardhat";
import "hardhat-gas-reporter";
import "solidity-coverage";

dotenv.config();

// This is a sample Hardhat task. To learn how to create your own go to
// https://hardhat.org/guides/create-task.html
task("accounts", "Prints the list of accounts", async (taskArgs, hre) => {
  const accounts = await hre.ethers.getSigners();

  for (const account of accounts) {
    console.log(account.address);
  }
});

// You need to export an object to set up your config
// Go to https://hardhat.org/config/ to learn more

const config: HardhatUserConfig = {
  solidity: "0.8.4",
  networks: {
    ropsten: {
      url: process.env.ROPSTEN_URL || "",
      accounts:
        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
    },
  },
  gasReporter: {
    enabled: process.env.REPORT_GAS !== undefined,
    currency: "USD",
  },
  etherscan: {
    apiKey: process.env.ETHERSCAN_API_KEY,
  },
};

export default config;

LoveLetter-base.sol

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

import "hardhat/console.sol";

contract LoveLetter {
    uint256 public totalLetters;
    mapping(uint256 => address) public senders;
    mapping(uint256 => address) public receivers;
    struct Letter {
        string message;
        uint256 etherAmount;
        bool opened;
    }
    mapping(uint256 => Letter) public letters;

    constructor() {
        totalLetters = 0;
    }
}

LoveLetter-checkOpened.sol

function checkOpened(uint256 id) external view returns (bool opened) {
    opened = letters[id].opened;
}

LoveLetter-getEtherAmount.sol

function getEtherAmount(uint256 id)
    external
    view
    returns (uint256 etherAmount)
{
    etherAmount = letters[id].etherAmount;
}

LoveLetter-getReceiver.sol

function getReceiver(uint256 id) external view returns (address receiver) {
    receiver = receivers[id];
}

LoveLetter-getSender.sol

function getSender(uint256 id) external view returns (address sender) {
    sender = senders[id];
}

LoveLetter-open.sol

function open(uint256 id) external returns (string memory message) {
    require(receivers[id] == msg.sender, "Not receiver");
    message = letters[id].message;
    letters[id].opened = true;
    uint256 amount = letters[id].etherAmount;
    console.log("open amount", amount);
    if (amount > 0) {
        payable(msg.sender).transfer(amount);
    }
}

LoveLetter-readMessage.sol

function readMessage(uint256 id)
    external
    view
    returns (string memory message)
{
    message = letters[id].message;
}

LoveLetter-send.sol

function send(address to, string memory message) external payable {
    senders[totalLetters] = msg.sender;
    receivers[totalLetters] = to;
    letters[totalLetters] = Letter({
        message: message,
        etherAmount: msg.value,
        opened: false
    });
    console.log("totalLetters", totalLetters);
    totalLetters++;
}

LoveLetter.sol

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

import "hardhat/console.sol";

contract LoveLetter {
    uint256 public totalLetters;
    mapping(uint256 => address) public senders;
    mapping(uint256 => address) public receivers;
    struct Letter {
        string message;
        uint256 etherAmount;
        bool opened;
    }
    mapping(uint256 => Letter) public letters;

    constructor() {
        totalLetters = 0;
    }

    function send(address to, string memory message) external payable {
        senders[totalLetters] = msg.sender;
        receivers[totalLetters] = to;
        letters[totalLetters] = Letter({
            message: message,
            etherAmount: msg.value,
            opened: false
        });
        console.log("totalLetters", totalLetters);
        totalLetters++;
    }

    function open(uint256 id) external returns (string memory message) {
        require(receivers[id] == msg.sender, "Not receiver");
        message = letters[id].message;
        letters[id].opened = true;
        uint256 amount = letters[id].etherAmount;
        console.log("open amount", amount);
        if (amount > 0) {
            payable(msg.sender).transfer(amount);
        }
    }

    function readMessage(uint256 id)
        external
        view
        returns (string memory message)
    {
        message = letters[id].message;
    }

    function checkOpened(uint256 id) external view returns (bool opened) {
        opened = letters[id].opened;
    }

    function getEtherAmount(uint256 id)
        external
        view
        returns (uint256 etherAmount)
    {
        etherAmount = letters[id].etherAmount;
    }

    function getSender(uint256 id) external view returns (address sender) {
        sender = senders[id];
    }

    function getReceiver(uint256 id) external view returns (address receiver) {
        receiver = receivers[id];
    }
}