Nexus Auctions 🔨

A decentralized auction application built on Ethereum, deployed on the Sepolia testnet. Nexus Auctions allows anyone to participate in auctions — placing bids, completing purchases, and withdrawing funds — all trustlessly on-chain, with owner-approved auction creation.

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Live Demo

Deployed on Sepolia Testnet Contract Address: 0xbb08e8ff7B8668B4039F04e70891BFAC017FE17e View on Sepolia Etherscan

Website: Nexus Auctions Get Ethereum Sepolia: Google Sepolia Faucet

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In-Progess

• Database Implementation (PostgreSQL)
• ERC-20 Token Implementation
• UI styling
• Upgradability (Proxy Pattern)

Features

• Owner-approved auctions — only the contract owner can create auctions, assigning a seller per auction
• Open bidding — anyone can place a bid above the current highest bid
• Automatic refunds — outbid participants are not refunded automatically; payment is only sent on completeTransaction
• Winner purchase flow — the highest bidder completes the purchase by sending the exact bid amount after the auction ends
• Seller withdrawal — sellers withdraw their funds after the winner completes the purchase
• Result announcements — anyone can announce results on-chain after an auction ends, emitting a verifiable event
• Auction cancellation — the owner can cancel an active auction at any time
• Role-based UI — the frontend shows different panels depending on whether you are the owner, seller, or winner

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Tech Stack

Smart Contract

• Solidity ^0.8.26
• Hardhat
• Deployed & verified on Sepolia testnet

Frontend

• React + Vite
• Wagmi v2
• Viem v2
• RainbowKit v2
• TanStack Query

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Project Structure

Nexus-Auctions/
├── Auction/                  # Hardhat project
│   ├── contracts/
│   │   └── Auction.sol       # Main auction smart contract
│   ├── scripts/
│   │   └── deploy.js         # Deployment script
│   ├── hardhat.config.js
│   └── package.json
├── src/                      # React frontend
│   ├── App.jsx               # Main UI component
│   ├── main.jsx              # Wagmi + RainbowKit providers
│   └── auction.js            # Contract ABI and address
├── public/
├── index.html
└── package.json

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Smart Contract

The Auction.sol contract supports the following functions:

Function	Access	Description
createAuction(seller, auctionNumber, startingPrice, duration)	Owner only	Creates a new auction
bid(auctionNumber, bidAmount)	Anyone	Places a bid above the current highest
cancelAuction(auctionNumber)	Owner only	Cancels an active auction
completeTransaction(auctionNumber)	Winner only	Winner sends ETH to complete the purchase
sellerWithdrawal(auctionNumber)	Seller only	Seller withdraws funds after purchase
announceResults(auctionNumber)	Anyone	Emits ResultsAnnounced event after auction ends
checkAuctionActive(auctionNumber)	View	Returns whether an auction is currently active
timeLeft(auctionNumber)	View	Returns seconds remaining in the auction
checkHighestBidder(auctionNumber)	View	Returns the current highest bidder address
checkActiveBidPrice(auctionNumber)	View	Returns the current highest bid amount

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How It Works

1. Owner creates an auction — specifying the seller address, auction number, starting price, and duration in seconds
2. Bidders place bids — any bid must be above the current highest bid (or above starting price for the first bid)
3. Auction ends — once the duration expires, no more bids are accepted
4. Results announced — anyone can call announceResults to emit a verifiable on-chain event
5. Winner completes purchase — the highest bidder calls completeTransaction, sending the exact bid amount in ETH
6. Seller withdraws — after the purchase is complete, the seller calls sellerWithdrawal to receive the funds

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Custom Errors

The contract uses custom errors for gas-efficient reverts:

• NotOwner — caller is not the contract owner
• AuctionAlreadyExists — auction number already in use
• AuctionDoesNotExist — auction number not found
• AuctionNotActive — auction has ended or been cancelled
• BidTooLow — bid is not above current highest bid
• LowerThanStartingPrice — first bid is below starting price
• YouAreNotTheWinner — only the highest bidder can complete the transaction
• YouAreNotTheSeller — only the assigned seller can withdraw
• WrongAmount — ETH sent does not match the winning bid
• AlreadyPurchased — purchase already completed
• AlreadyWithdrawn — seller has already withdrawn funds
• NoBidders — no bids were placed before auction ended

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License

MIT