Purchase

purchase.sol

contract Purchase {
    address public seller;
    address public buyer;
    uint256 public price;
    
    enum State { Created, BuyerConfirmed, ProductReturned, Finished }
    State state;
    
    function Purchase() {
        seller = msg.sender;
        price = msg.value / 2;
        state = State.Created;
    }
    
    event BuyerConfirmed(address buyer);
    
    function ConfirmPurchase() {
        if (state != State.Created) throw;
        if (msg.value != 2 * price) throw;
        
        buyer = msg.sender;
        state = State.BuyerConfirmed;
        
        BuyerConfirmed(buyer);
    }
    
    event ProductReceivedOk();
    
    function ConfirmProductReceivedOk() {
        if (state != State.BuyerConfirmed) throw;
        if (buyer != msg.sender) throw;
        
        seller.send(3 * price);
        buyer.send(1 * price);
        
        state = State.Finished;
        
        ProductReceivedOk();
    }
    
    event ProductReturned();
    
    function ConfirmProductReturned() {
        if (state != State.BuyerConfirmed) throw;
        if (buyer != msg.sender) throw;
        
        state = State.ProductReturned;
        
        ProductReturned();
    }
    
    event Refunded();
    
    function ConfirmReturnedProductReceived() {
        if (state != State.ProductReturned) throw;
        if (seller != msg.sender) throw;
        
        seller.send(2 * price);
        buyer.send(2 * price);
        
        state = State.Finished;
        
        Refunded();
    }
    
}