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sellItems.js
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sellItems.js
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import { Fail } from '@endo/errors';
import { Far } from '@endo/marshal';
import { Nat } from '@endo/nat';
import { AmountMath } from '@agoric/ertp';
import {
makeNotifierKit,
observeIteration,
subscribeLatest,
} from '@agoric/notifier';
import {
assertIssuerKeywords,
defaultAcceptanceMsg,
assertProposalShape,
assertNatAssetKind,
} from '../contractSupport/index.js';
/**
* Sell items in exchange for money. Items may be fungible or
* non-fungible and multiple items may be bought at once. Money must
* be fungible.
*
* The `pricePerItem` is to be set in the terms. It is expected that all items
* are sold for the same uniform price.
*
* The initial offer should be { give: { Items: items } }, accompanied by
* terms as described above.
* Buyers use offers that match { want: { Items: items } give: { Money: m } }.
* The items provided should match particular items that the seller still has
* available to sell, and the money should be pricePerItem times the number of
* items requested.
*
* When all the items have been sold, the contract will terminate, triggering
* the creator's payout. If the creator has an onDemand exit clause, they can
* exit early to collect their winnings. The remaining items will still be
* available for sale, but the creator won't be able to collect later earnings.
*
* @param {ZCF<{pricePerItem: Amount<'nat'>}>} zcf
*/
const start = zcf => {
const { pricePerItem, issuers, brands } = zcf.getTerms();
const allKeywords = ['Items', 'Money'];
assertIssuerKeywords(zcf, harden(allKeywords));
assertNatAssetKind(zcf, pricePerItem.brand);
let sellerSeat;
const { notifier: availableItemsNotifier, updater: availableItemsUpdater } =
makeNotifierKit();
const sell = seat => {
sellerSeat = seat;
void observeIteration(
subscribeLatest(sellerSeat.getSubscriber()),
harden({
updateState: sellerSeatAllocation =>
availableItemsUpdater.updateState(
sellerSeatAllocation && sellerSeatAllocation.Items,
),
finish: sellerSeatAllocation => {
availableItemsUpdater.finish(
sellerSeatAllocation && sellerSeatAllocation.Items,
);
},
fail: reason => availableItemsUpdater.fail(reason),
}),
);
availableItemsUpdater.updateState(sellerSeat.getCurrentAllocation().Items);
return defaultAcceptanceMsg;
};
const getAvailableItems = () => {
assert(sellerSeat && !sellerSeat.hasExited(), 'no items are for sale');
return sellerSeat.getAmountAllocated('Items');
};
const getAvailableItemsNotifier = () => availableItemsNotifier;
const buy = buyerSeat => {
assertProposalShape(buyerSeat, {
want: { Items: null },
give: { Money: null },
});
const currentItemsForSale = sellerSeat.getAmountAllocated('Items');
const providedMoney = buyerSeat.getAmountAllocated('Money');
const {
want: { Items: wantedItems },
} = buyerSeat.getProposal();
// Check that the wanted items are still for sale.
if (!AmountMath.isGTE(currentItemsForSale, wantedItems)) {
const rejectMsg = `Some of the wanted items were not available for sale`;
throw buyerSeat.fail(Error(rejectMsg));
}
// All items are the same price.
const totalCost = AmountMath.make(
brands.Money,
pricePerItem.value * Nat(wantedItems.value.length),
);
// Check that the money provided to pay for the items is greater than the totalCost.
AmountMath.isGTE(providedMoney, totalCost) ||
Fail`More money (${totalCost}) is required to buy these items`;
// Reallocate.
zcf.atomicRearrange(
harden([
[buyerSeat, sellerSeat, { Money: providedMoney }],
[sellerSeat, buyerSeat, { Items: wantedItems }],
]),
);
// The buyer's offer has been processed.
buyerSeat.exit();
if (AmountMath.isEmpty(getAvailableItems())) {
zcf.shutdown('All items sold.');
} else {
availableItemsUpdater.updateState(
sellerSeat.getCurrentAllocation().Items,
);
}
return defaultAcceptanceMsg;
};
const makeBuyerInvitation = () => {
const itemsAmount = sellerSeat.getAmountAllocated('Items');
assert(
sellerSeat && !AmountMath.isEmpty(itemsAmount),
'no items are for sale',
);
return zcf.makeInvitation(buy, 'buyer');
};
/** @type {SellItemsPublicFacet} */
const publicFacet = Far('SellItemsPublicFacet', {
getAvailableItems,
getAvailableItemsNotifier,
getItemsIssuer: () => issuers.Items,
makeBuyerInvitation,
});
/** @type {SellItemsCreatorFacet} */
const creatorFacet = Far('SellItemsCreatorFacet', {
makeBuyerInvitation,
getAvailableItems: publicFacet.getAvailableItems,
getItemsIssuer: publicFacet.getItemsIssuer,
});
const creatorInvitation = zcf.makeInvitation(sell, 'seller');
return harden({ creatorFacet, creatorInvitation, publicFacet });
};
harden(start);
export { start };