Shared Expense Settlement

What it does:
Enables groups to record, split, and settle shared expenses transparently on-chain, automating contributions, reimbursements, and balances.

Why it matters:
Eliminates disputes over who paid what, ensures fair settlement, prevents errors, and provides immutable records for all participants.

How it works:

Group members add expenses specifying amount, payer, and involved participants
Smart contract calculates owed balances automatically
Members can settle their shares by sending funds to the contract
Automatic reimbursement is triggered when contributions cover owed amounts
Integrates with Personal Wallets, Tokenized Payments, or Event Planning Escrow
Dashboards display group balances, pending payments, and history of settlements

      // SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/access/Ownable.sol";

/**
 * @title SharedExpenseSettlement
 * @author Nam
 * @notice Tracks group expenses and automates settlement on-chain
 */
contract SharedExpenseSettlement is Ownable {

    struct Expense {
        string description;
        uint256 amount;
        address payer;
        address[] participants;
        bool settled;
    }

    mapping(uint256 =&gt; Expense) public expenses;
    uint256 public expenseCount;

    mapping(address =&gt; mapping(address =&gt; uint256)) public balances; // who owes whom

    // -------------------- EVENTS --------------------

    event ExpenseAdded(uint256 indexed expenseId, string description, uint256 amount, address payer);
    event SettlementPaid(address from, address to, uint256 amount);

    // -------------------- EXPENSE MANAGEMENT --------------------

    function addExpense(string calldata _description, uint256 _amount, address[] calldata _participants) external {
        require(_amount &gt; 0, "Amount must be &gt; 0");
        require(_participants.length &gt; 0, "No participants");

        expenseCount += 1;
        expenses[expenseCount] = Expense({
            description: _description,
            amount: _amount,
            payer: msg.sender,
            participants: _participants,
            settled: false
        });

        uint256 share = _amount / _participants.length;
        for (uint256 i = 0; i  0, "No balance owed");
        require(msg.value == owed, "Incorrect payment amount");

        balances[msg.sender][_to] = 0;
        payable(_to).transfer(msg.value);

        emit SettlementPaid(msg.sender, _to, msg.value);
    }

    // -------------------- VIEW FUNCTIONS --------------------

    function getOwedBalance(address _from, address _to) external view returns (uint256) {
        return balances[_from][_to];
    }
}