Introduction

Your task is to implement a basic Auction using a smart contract which grants its creator the ability to initiate and manage a public auction.

Contract interface description

1. Auction constructor:

• should set seller field to contract creator,
• should set latestBid field to the startingPrice (in Wei).

2. Payable bid function:

• is used to place a new bid,
• should revert if auction is already finished,
• should return previous bid to the bidder.

3. finishAuction function:

• is used to manually finish the auction,
• should revert if auction is already finished,
• should withdraw winning bid to the seller,
• should be callable only by the auction owner.

You should not change public contract interfaces, i.e. seller, latestBid, latestBidder fields and bid, finishAuction methods should remain accessible by external components and tests.