2. Development Setup for Hardhat on Visual Studio Code

This guide will help you set up Microsoft Visual Studio Code for Hardhat, a popular development framework for Ethereum smart contracts.

Prerequisites

Before you start, make sure you have the following installed:

• Node.js (v18+ recommended)
• Visual Studio Code
• MetaMask browser extension
• Git (optional but recommended)

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Setting Up Your Hardhat Project

Step 1: Initialize a New Hardhat Project

1. Open VS Code and open a new terminal.
2. Run the following command to create a new project:

   mkdir hardhat-todo && cd hardhat-todo
   npm init -y
   npm install --save-dev hardhat
3. Initialize Hardhat:

   npx hardhat
4. Select Create a Typescript project and follow the instructions.

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Writing a Smart Contract (TodoList.sol)

Below is an explanation of the TodoList smart contract and its components.

1. Contract Structure

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract TodoList {

• pragma solidity ^0.8.24; → Ensures compatibility with Solidity compiler version 0.8.24 or later.
• contract TodoList { → Defines the contract named TodoList.

2. Task Structure

    struct Task {
        uint32 id;
        string task;
        bool completed;
    }

• Task struct represents a to-do item with an ID, description, and completion status.

3. User Task Management

    struct UserTasks {
        uint32 taskCount;
        mapping(uint32 => Task) tasks;
    }

    mapping(address => UserTasks) private userTasks;

• UserTasks struct stores all tasks for each user.
• mapping(address => UserTasks) private userTasks; → Maps user addresses to their task lists.

4. Events

    event TaskCreated(address user, uint32 id, string task, bool completed);
    event TaskCompleted(address user, uint32 id, bool completed);
    event TaskUpdated(address user, uint32 id, string task);
    event TaskRemoved(address user, uint32 id);

• These events help log contract activity for front-end applications.

5. Retrieve Tasks

    function getTasks() external view returns (Task[] memory) {
        UserTasks storage userTaskList = userTasks[msg.sender];
        Task[] memory taskList = new Task[](userTaskList.taskCount);
        for (uint32 i = 0; i < userTaskList.taskCount; i++) {
            taskList[i] = userTaskList.tasks[i];
        }
        return taskList;
    }

• Returns an array of tasks for the caller’s address.

6. Creating a Task

    function createTask(string memory _task) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        userTaskList.tasks[userTaskList.taskCount] = Task({
            id: userTaskList.taskCount,
            task: _task,
            completed: false
        });
        userTaskList.taskCount++;
        emit TaskCreated(msg.sender, userTaskList.taskCount, _task, false);
    }

• Creates a new task for the user and emits the TaskCreated event.

7. Updating a Task

    function updateTask(uint32 _id, string memory _task) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        require(_id <= userTaskList.taskCount, "Task does not exist");
        userTaskList.tasks[_id].task = _task;
        emit TaskUpdated(msg.sender, _id, _task);
    }

• Updates the task description based on the provided ID.

8. Completing a Task

    function completeTask(uint32 _id) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        require(_id <= userTaskList.taskCount, "Task does not exist");
        userTaskList.tasks[_id].completed = true;
        emit TaskCompleted(msg.sender, _id, true);
    }

• Marks a task as completed.

9. Removing a Task

    function removeTask(uint32 _id) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        require(_id < userTaskList.taskCount, "Task does not exist");
        if (_id != userTaskList.taskCount - 1) {
            userTaskList.tasks[_id] = userTaskList.tasks[userTaskList.taskCount - 1];
            userTaskList.tasks[_id].id = _id;
        }
        delete userTaskList.tasks[userTaskList.taskCount - 1];
        userTaskList.taskCount--;
        emit TaskRemoved(msg.sender, _id);
    }

• Deletes a task and maintains mapping integrity.

10. Full Smart Contract Code

    // SPDX-License-Identifier: MIT

pragma solidity ^0.8.24;

contract TodoList {
    struct Task {
        uint32 id;
        string task;
        bool completed;
    }

    struct UserTasks {
        uint32 taskCount;
        mapping(uint32 => Task) tasks;
    }

    mapping(address => UserTasks) private userTasks;

    event TaskCreated(address user, uint32 id, string task, bool completed);
    event TaskCompleted(address user, uint32 id, bool completed);
    event TaskUpdated(address user, uint32 id, string task);
    event TaskRemoved(address user, uint32 id);

    function getTasks() external view returns (Task[] memory) {
        UserTasks storage userTaskList = userTasks[msg.sender];
        Task[] memory taskList = new Task[](userTaskList.taskCount);
        for (uint32 i = 0; i < userTaskList.taskCount; i++) {
            taskList[i] = userTaskList.tasks[i];
        }
        return taskList;
    }

    function getTask(uint32 _id) external view returns (Task memory) {
        return userTasks[msg.sender].tasks[_id];
    }

    function createTask(string memory _task) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        userTaskList.tasks[userTaskList.taskCount] = Task({
            id: userTaskList.taskCount,
            task: _task,
            completed: false
        });
        userTaskList.taskCount++;
        emit TaskCreated(msg.sender, userTaskList.taskCount, _task, false);
    }

    function updateTask(uint32 _id, string memory _task) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        require(_id <= userTaskList.taskCount, "Task does not exist");
        userTaskList.tasks[_id].task = _task;
        emit TaskUpdated(msg.sender, _id, _task);
    }

    function removeTask(uint32 _id) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        require(_id < userTaskList.taskCount, "Task does not exist");
        if (_id != userTaskList.taskCount - 1) {
            // Move the last task to the position of the task to be deleted
            userTaskList.tasks[_id] = userTaskList.tasks[userTaskList.taskCount - 1];
            userTaskList.tasks[_id].id = _id; // Update the id of the moved task
        }
        delete userTaskList.tasks[userTaskList.taskCount - 1];
        userTaskList.taskCount--;
        emit TaskRemoved(msg.sender, _id);
    }

    function completeTask(uint32 _id) external {
        UserTasks storage userTaskList = userTasks[msg.sender];
        require(_id <= userTaskList.taskCount, "Task does not exist");
        userTaskList.tasks[_id].completed = true;
        emit TaskCompleted(msg.sender, _id, true);
    }
}

Now, your TodoList Smart Contract is ready to deploy! 🚀