Dria

Summary:

function purchase(address _asset) external {
AssetListing storage listing = listings[_asset];

    // asset must be listed to be purchased
    if (listing.status != AssetStatus.Listed) {
        revert InvalidStatus(listing.status, AssetStatus.Listed);
    }

    // can only the buyer can purchase the asset
    if (listing.buyer != msg.sender) {
        revert Unauthorized(msg.sender);
    }

    // update asset status to be sold
    listing.status = AssetStatus.Sold;

    // transfer asset from seller to Swan, and then from Swan to buyer
    // this ensure that only approval to Swan is enough for the sellers

@> SwanAsset(_asset).transferFrom(listing.seller, address(this), 1);
@> SwanAsset(_asset).transferFrom(address(this), listing.buyer, 1);

    // transfer money

@> token.transferFrom(listing.buyer, address(this), listing.price);
@> token.transfer(listing.seller, listing.price);