How to multisig a transaction function?

Question

I have a smart contract for selling Painting in crowdsale, Once the Painting is sold in crowdsale the owner of the painting can trade it to other user once the crowdsale is over. I have to implement a buy function where the buyer can buy the painting only if the seller has interest to sell it.The problem I am facing is that How can a buyer know whether the seller is interested and at what cost is he comfortable to sell? Once solution I have thought is that to make the function multisig where both buyer and seller need to sign to transfer the painting and accept the Payment.

Ps :- How to implement multisig feature to a function to sign

Answer 1

Assume the painting ownerships are stored in a mapping, you can create, another mapping where the owner set if he wants to sell it or not, for instance:

mapping(address => uint256) public paintingOwnership; // this assumes the painting id is a number
mapping(uint256 => bool) public sellStatus;

function buy(uint256 paintingID) public {
    require(sellStatus[paintingID],"Painting is not for sale")
    // do here the required to make the transaction between tokens/ether and the painting
}

function changeSellStatus(bool value) public {
    require(paintingOwnership[msg.sender] > 0);
    uint paintingID = paintingOwnership[msg.sender];
    sellStatus[paintingId] = value;
}

function availability(uint256 paintingID) public pure returns(bool){
    return sellStatus[paintingId];
}

The function buy will be executed by the buyer and will only be executed if the painting is for sell. Buyers can also check availablity with the function provided. The seller will use changeSellStatus to set if they want to sell (True) or not (False).

Hope this helps.