📜 Auction Smart Contract

This is part of a Eth Kipu blockchain development course assignment. It's a smart contract to create an auction system on the Ethereum blockchain.

📝 Overview

This Solidity smart contract facilitates a bidding process where users can place bids within a defined time frame. It includes advanced features such as automatic time extensions, refunds with commission deductions, and secure deposit management.

⚙️ Key Features

📌 Minimum bid increment: Every new bid must be at least 5% higher than the current highest bid.

⏳ Automatic time extension: If a bid is placed within the last 10 minutes of the auction, the deadline is extended.

💰 Refund mechanism: Participants can withdraw their deposits, subject to a 2% fee.

🔐 Access controls: Modifiers regulate contract execution to ensure integrity.

🚀 Implementation Details

Built on Solidity 0.8.0, this contract leverages mappings, structs, and arrays for efficient data handling. It prioritizes security by mitigating overflow risks and enforcing proper bid validations.

🔄 State Variables

The contract includes several key variables that store auction-related data:

1. General Variables

• owner (address) Stores the contract owner's address.

• objectValue (address) Value of the auctions object.

• auctionEndTime (uint256) Timestamp indicating when the auction ends.

• highestBid (uint256) Current highest bid amount.

• highestBidder (address) Address of the highest bidder.

• ended (bool) Whether the auction has ended.

2. Constants

• EXTENSION_TIME (uint256) Auction time extension (10 minutes).

• INCREMENT_PERCENT (uint256) Minimum bid increment percentage (5%).

• COMMISSION_PERCENT (uint256) Refund commission percentage (2%).

3. Mappings and Structs

• userBids (mapping(address => UserBid[])) Tracks all bids placed by a user.

• deposits (mapping(address => uint256)) Stores total deposit amounts per user.

• lastBids (mapping(address => Bid)) Keeps record of users’ latest bids.

• hasBid (mapping(address => bool)) Checks whether a user has bid.

• userTotalBids (mapping(address => uint256)) Stores total bid amounts per user.

🎟️ Events

The contract emits events to notify external applications about important actions:

• NewBid(address indexed bidder, uint256 amount) Emitted when a new bid is placed.

• AuctionEnded(address winner, uint256 winningBid) Emitted when the auction ends, declaring a winner.

• RefundBids(address indexed beneficiary, uint256 amount) Emitted when refunds are processed for bidders who did not win.

🔍 Core Functions

1. 🔄 Bid Management

bid()

• Places a new bid in the auction

• Requires:

  • Bid value ≥ current highest + 5%

  • Auction must be active

• Emits: BidPlaced

_minBid() private view → (uint256)

• Calculates minimum acceptable bid

• Returns: Minimum bid amount (current highest + 5%)

2. ⏹️ Auction Control

endAuction()

• Officially ends auction and distributes winning bid

• Requires:

  • Owner only

  • Auction time expired

• Emits: AuctionEnded

refundAllNonWinners()

• Processes refunds for all non-winning bidders (minus 2% fee)

• Emits: Refund for each processed bid

3. 💰 Withdrawals

withdrawExcess(uint256 _amount)

• Allows partial withdrawal of excess funds during auction

• Parameters:

  • _amount: Amount to withdraw

claimRefund()

• Lets non-winning bidders claim refund after auction ends

• Deducts: 2% commission fee

4. 👑 Owner Functions

setPaused(bool _paused)

• Pauses/unpauses the auction

• Emits: Paused

emergencyWithdraw(uint256 _amount)

• Owner-only emergency ETH recovery

• For: Stuck funds only

5. 🔍 View Functions getWinner() → (address winner, uint256 amount)

• Returns auction winner information

getAllBids() → (Bid[] memory)

• Returns complete bid history

getUserBids(address _bidder) → (UserBid[] memory)

• Returns specific user's bid history

getAllBidders() → (address[] memory)

-Returns list of all participants

📜 License

This contract is licensed under MIT.