🧾Implementing Transactions with Smart Contracts

Certainly, We'll provide a simplified example of a Solidity smart contract for a real estate transaction scenario involving a contract owner, a buyer, and a seller.

This example focuses on the core functionalities, and in a real-world scenario, additional features and security measures would be needed.

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

contract BitEstateTransaction {
    address public contractOwner;
    address public buyer;
    address public seller;
    
    enum ContractState { InProgress, Completed, Cancelled }
    ContractState public state;

    struct Property {
        string propertyId;
        string propertyDetails;
        uint256 price;
        bool isListed;
    }
    
    Property public property;

    event PropertyListed(string propertyId, uint256 price);
    event OfferSubmitted(address buyer, uint256 offerAmount);
    event OfferAccepted(address buyer, uint256 offerAmount);
    event TransactionCompleted(address buyer, address seller, uint256 finalPrice);

    modifier onlyOwner() {
        require(msg.sender == contractOwner, "Only the contract owner can call this function");
        _;
    }

    modifier onlyBuyer() {
        require(msg.sender == buyer, "Only the buyer can call this function");
        _;
    }

    modifier onlySeller() {
        require(msg.sender == seller, "Only the seller can call this function");
        _;
    }

    modifier inProgress() {
        require(state == ContractState.InProgress, "Transaction is not in progress");
        _;
    }

    constructor() {
        contractOwner = msg.sender;
        state = ContractState.InProgress;
    }

    function listProperty(string memory _propertyId, string memory _propertyDetails, uint256 _price) external onlyOwner inProgress {
        property.propertyId = _propertyId;
        property.propertyDetails = _propertyDetails;
        property.price = _price;
        property.isListed = true;

        emit PropertyListed(_propertyId, _price);
    }

    function submitOffer() external payable inProgress {
        require(property.isListed, "Property is not listed");
        require(msg.sender != seller, "Seller cannot submit an offer");

        emit OfferSubmitted(msg.sender, msg.value);
    }

    function acceptOffer() external onlyOwner inProgress {
        require(property.isListed, "Property is not listed");

        buyer = msg.sender;
        seller = payable(msg.sender);
        state = ContractState.Completed;

        emit OfferAccepted(buyer, property.price);

        // Transfer funds to the seller
        seller.transfer(property.price);
    }

    function cancelTransaction() external onlyOwner {
        require(state == ContractState.InProgress, "Transaction is not in progress");
        state = ContractState.Cancelled;
    }

    function completeTransaction() external onlyOwner inProgress {
        require(buyer != address(0), "No valid buyer");
        
        state = ContractState.Completed;
        emit TransactionCompleted(buyer, seller, property.price);

        // Transfer funds to the seller
        seller.transfer(property.price);
    }
}

Scenario for the Contract Owner:

1. The contract owner deploys the smart contract.

2. The contract owner lists a property with specific details and a price.

3. The contract owner can cancel the transaction if needed.

Scenario for a Buyer:

1. A buyer submits an offer by calling the submitOffer function and sending the required amount of ether.

2. The contract emits an OfferSubmitted event.

Scenario for a Seller:

1. The contract owner (acting as the seller) accepts the offer by calling the acceptOffer function.

2. The contract transitions to the Completed state.

3. The contract emits an OfferAccepted event.