mkdir todolist
cd todolist
npm init -y
npm install --save-dev hardhat

npx hardhat init

code .

npm i dotenv

require("@nomicfoundation/hardhat-toolbox");
require("dotenv").config();

module.exports = {
  solidity: "0.8.19",

  networks: {
    sepolia: {
      url: process.env.ALCHEMY_API_KEY_URL,
      accounts: [process.env.PRIVATE_KEY],
    },
  },
};

// SPDX-License-Identifier: MIT

// Solidity Version
pragma solidity 0.8.19;

contract TodoList {
    // Struct to represent a task
    struct Task {
        uint id; // Unique task identifier
        uint date; // Timestamp of task creation
        string name; // Task name
        string description; // Task description
        bool isCompleted; // Flag indicating task completion status
        address owner; // Address of the task owner
    }

    // Array to store all tasks
    Task[] public tasks;

    // Mapping to associate user addresses with their task IDs
    mapping(address => uint[]) private userTasks;

    // Constructor function
    constructor() {}

    // Event emitted when a task is created
    event TaskCreated(
        uint id,
        uint date,
        string name,
        string description,
        bool isCompleted,
        address owner
    );

    // Event emitted when a task is marked as completed
    event TaskCompleted(uint id, address owner);

    // Event emitted when a task is deleted
    event TaskDeleted(uint id, address owner);

    // Function to create a new task
    function createTask(string memory name, string memory description) public {
        uint taskId = tasks.length; // Calculate the new task ID
        tasks.push(
            Task(taskId, block.timestamp, name, description, false, msg.sender)
        ); // Create and add the new task to the array
        userTasks[msg.sender].push(taskId); // Update the userTasks mapping
        emit TaskCreated(
            taskId,
            block.timestamp,
            name,
            description,
            false,
            msg.sender
        ); // Emit a TaskCreated event
    }

    // Function to retrieve task details by ID
    function getTask(
        uint id
    )
        public
        view
        returns (uint, uint, string memory, string memory, bool, address)
    {
        // Ensure the task ID is valid
        require(id < tasks.length, "Task ID does not exist"); 
        Task storage task = tasks[id]; // Retrieve the task from storage
        return (
            task.id,
            task.date,
            task.name,
            task.description,
            task.isCompleted,
            task.owner
        ); // Return task details
    }

    // Function to mark a task as completed
    function markTaskCompleted(uint id) public {
        // Ensure the task ID is valid
        require(id < tasks.length, "Task ID does not exist"); 
        Task storage task = tasks[id]; // Retrieve the task from storage
        require(
            task.owner == msg.sender,
            "Only the owner can complete the task"
        );
        // Ensure the task is not already completed
        require(!task.isCompleted, "Task is already completed"); 
        task.isCompleted = true; // Mark the task as completed
        emit TaskCompleted(id, msg.sender); // Emit a TaskCompleted event
    }

    // Function to delete a task
    function deleteTask(uint id) public {
        // Ensure the task ID is valid
        require(id < tasks.length, "Task ID does not exist"); 
        Task storage task = tasks[id]; // Retrieve the task from storage
        // Ensure only the owner can delete the task
        require(task.owner == msg.sender, "Only the owner can delete the task"); 
        emit TaskDeleted(id, msg.sender); // Emit a TaskDeleted event

        // Delete the task by replacing it with the last task in the array 
        // and reducing the array size
        uint lastIndex = tasks.length - 1;
        if (id != lastIndex) {
            Task storage lastTask = tasks[lastIndex];
            tasks[id] = lastTask;
            userTasks[msg.sender][id] = lastIndex;
        }
        tasks.pop();
        userTasks[msg.sender].pop();
    }

    // Function to retrieve all task IDs belonging to the caller
    function getUserTasks() public view returns (uint[] memory) {
        // Return the task IDs associated with the caller's address
        return userTasks[msg.sender]; 
    }
}

const { expect } = require("chai");
const { ethers } = require("hardhat");

describe("TodoList contract", function () {
  let TodoList;
  let todolist;
  let owner;

  before(async function () {
    [owner] = await ethers.getSigners();

    // Deploy the TodoList contract
    todolist = await ethers.deployContract("TodoList");
    // await TodoList.waitForDeployment();
  });

  it("should create a new task", async function () {
    const taskName = "Sample Task";
    const taskDescription = "This is a sample task description";

    // Create a new task
    await todolist.createTask(taskName, taskDescription);

    // Retrieve the task details
    const [id, date, name, description, isCompleted, taskOwner] =
      await todolist.getTask(0);

    expect(id).to.equal(0);
    expect(name).to.equal(taskName);
    expect(description).to.equal(taskDescription);
    expect(isCompleted).to.equal(false);
    expect(taskOwner).to.equal(owner.address);
  });

  it("should mark a task as completed", async function () {
    // Mark the task at index 0 as completed
    await todolist.markTaskCompleted(0);

    // Retrieve the task details
    const [, , , , isCompleted] = await todolist.getTask(0);

    expect(isCompleted).to.equal(true);
  });

  it("should delete a task", async function () {
    // Create a new task
    await todolist.createTask(
      "Task to be deleted",
      "This task will be deleted"
    );

    // Delete the task at index 1
    await todolist.deleteTask(1);

    // Attempt to retrieve the deleted task (should throw an error)
    let errorOccurred = false;
    try {
      await todolist.getTask(1);
    } catch (error) {
      errorOccurred = true;
    }

    expect(errorOccurred).to.equal(true);
  });

  it("should retrieve the user's tasks", async function () {
    // Create a new task
    await todolist.createTask("User's Task", "This is the user's task");

    // Retrieve the user's tasks
    const userTasks = await todolist.getUserTasks();

    // Expect that there is at least one task
    expect(userTasks.length).to.be.at.least(1);
  });
});

npx hardhat test

// Import the ethers library from the Hardhat framework
const { ethers } = require("hardhat");

// Define an asynchronous main function for contract deployment
async function main() {
  // Deploy the contract
  const TodoList = await ethers.deployContract("TodoList");

  // Log message to show deployment in progress
  console.log("Deploying contract.....");

  // Wait for the deployment of the contract to complete
  await TodoList.waitForDeployment();

  // Log the deployment target (contract address) to the console
  console.log(`TodoList deployed to ${TodoList.target}`);
}

// Execute the main function, and handle any errors that may occur
main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

npx hardhat run scripts/deploy.js --network sepolia