Introduction.

Hello, World!

Sometimes when you works like freelancer you don't sure about employer, for example: you can think that you made, sent the whole work and "employer" never pays to you, but instead if you are the employer, maybe you pay for a job that never exist it.

So, how can i make this transaction surer for me? 

I made this smart contract like practice, it has three functions:

• Employer deposit eth in smart contract, deposit().
• Freelancer upload data, like a link with his work, upload().
• Withdraw ether. withdraw(). 

Maybe for the employer this isn't 100% safe but freelancer, it is.  The problem is when owner upload link where it's all  work's information, he could upload something like this: https://www.ididntityouareasilly.com and the code still runing.

Code.

State variables.

address owner; // Contract owner.
address buyer; // Employer.
bool isDeposit; //Deposit is false
bool isUpload; // Upload is false
string link; // Data
uint priceService; // Work's price

Event.

There are two events, one when the employer deposit eth and the second, the freelancer upload data.

event Deposited(uint _amount, address _user);
event Uploaded(string data, address _user);

Constructor.

The constructor accepts two parameters: employer's address and work's price.

constructor(address _buyer, uint _cost) {
        owner = msg.sender;
        buyer = _buyer; 
        priceService = _cost;
    }

Modifier.

There are two modifiers, both work restricting access to functions. 

 modifier Owner() {
       require(owner == msg.sender);
        _;
    }

modifier MyBuyer() {
        require(buyer == msg.sender);
        _;
    }

Functions.

How i said before, this smart contract has three functions, im going to explan each one:

Deposit function:

function deposit() public payable MyBuyer {
        require(msg.value == getPriceRate(priceService), "Verify pay.");
        uint amount = msg.value;
        isDeposit = true;
        emit Deposited(amount, msg.sender);
    }

It uses when employer(MyBuyer) deposit eth inside the contract, when the condition is true, isDeposit is activated and event is emited,  getPriceRate came from this Chainlink code:

Chainlink get price:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

contract PriceConsumerV3 {

    AggregatorV3Interface internal priceFeed;

    constructor() {
        //Rinkeby address
        priceFeed = AggregatorV3Interface(0x8A753747A1Fa494EC906cE90E9f37563A8AF630e);
    }

    function getPriceRate(uint _amount) public view returns (uint) {
        (, int price,,,) = priceFeed.latestRoundData();
        uint adjust_price = uint(price) * 1e10;
        uint usd = _amount * 1e18;
        uint rate = (usd * 1e18) / adjust_price;
        return rate;
    }
}

Upload function:

Its similar to deposit function, it just need the bool isDeposit be true and owner has to upload his work.

function upload(string memory _link) public Owner {
        require(isDeposit == true, "Wait for deposit.");
        link = _link;
        isUpload = true;
        emit Uploaded(link, owner);
    }

Withdraw function:

function withdraw() public payable Owner {
        require(address(this).balance > 0, "There's not money.");
        require(isUpload == true, "Owner has to add document.");
        isDeposit = false;
        isUpload = false;
        payable(owner).transfer(address(this).balance);
    }

If all conditions are true, owner can use this function and recieve his money.

Full code (whitout chainlink api) :

//SPDX-License-Identifier: MIT
pragma solidity 0.8.7;

import "./Price.sol";

contract work is PriceConsumerV3 {
    
    address owner;
    address buyer;

    bool isDeposit;
    bool isUpload;

    string link;

    uint priceService;

    event Deposited(uint _amount, address _user);
    event Uploaded(string data, address _user);

    constructor(address _buyer, uint _cost) {
        owner = msg.sender;
        buyer = _buyer; 
        priceService = _cost;
    }

    modifier Owner() {
        require(owner == msg.sender);
        _;
    }

    modifier MyBuyer() {
        require(buyer == msg.sender);
        _;
    }

    function deposit() public payable MyBuyer {
        require(msg.value == getPriceRate(priceService), "Verify pay.");
        uint amount = msg.value;
        isDeposit = true;
        emit Deposited(amount, msg.sender);
    }

    function upload(string memory _link) public Owner {
        require(isDeposit == true, "Wait for deposit.");
        link = _link;
        isUpload = true;
        emit Uploaded(link, owner);
    }

    function withdraw() public payable Owner {
        require(address(this).balance > 0, "There's not money.");
        require(isUpload == true, "Owner has to add document.");
        isDeposit = false;
        isUpload = false;
        payable(owner).transfer(address(this).balance);
    }
}

Sorry if i didnt write clear, Spanish is my native lenguage and i'm learning English.   If you have any question or i made some mistake, you can ask me in comments section or :

• Twitter:  @Juan_saldano01
• Telegram: Juan_saldano
• Gmail: juansaldano01@gmail.com