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fix: lexical balance simplifies issuer code (#1889)
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@erights
erights authored Oct 22, 2020
1 parent 18c0314 commit 224b39a
Showing 1 changed file with 41 additions and 87 deletions.
128 changes: 41 additions & 87 deletions packages/ERTP/src/issuer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,8 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
);

const amountMath = makeAmountMath(brand, amountMathKind);
const { add } = amountMath;
const empty = amountMath.getEmpty();

const {
makeInstance: makePayment,
Expand All @@ -49,9 +51,6 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
/** @type {WeakStore<Payment, Amount>} */
const paymentLedger = makePaymentWeakStore();

/** @type {WeakStore<Purse, Amount>} */
let purseLedger;

function assertKnownPayment(payment) {
assert(
paymentLedger.has(payment),
Expand Down Expand Up @@ -83,10 +82,9 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
}),
);

const {
makeInstance: makePurse,
makeWeakStore: makePurseWeakStore,
} = makeExternalStore('purse', () => {
const { makeInstance: makePurse } = makeExternalStore('purse', () => {
let currentBalance = amountMath.getEmpty();

/** @type {Purse} */
const purse = Remotable(
makeInterface(allegedName, ERTPKind.PURSE),
Expand All @@ -102,39 +100,29 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
const srcPaymentBalance = paymentLedger.get(srcPayment);
// Note: this does not guarantee that optAmount itself is a valid stable amount
assertAmountEqual(srcPaymentBalance, optAmount);
const purseBalance = purse.getCurrentAmount();
const newPurseBalance = amountMath.add(
srcPaymentBalance,
purseBalance,
currentBalance,
);
// Commit point
// eslint-disable-next-line no-use-before-define
const payments = reallocate(
harden({
payments: [srcPayment],
purses: [purse],
newPurseBalances: [newPurseBalance],
}),
);
assert(payments.length === 0, 'no payments should be returned');
// Move the assets in `srcPayment` into this purse, using up the
// source payment, such that total assets are conserved.
paymentLedger.delete(srcPayment);
currentBalance = newPurseBalance;
return srcPaymentBalance;
},
withdraw: amount => {
amount = amountMath.coerce(amount);
const purseBalance = purse.getCurrentAmount();
const newPurseBalance = amountMath.subtract(purseBalance, amount);
const newPurseBalance = amountMath.subtract(currentBalance, amount);
const payment = makePayment();
// Commit point
// eslint-disable-next-line no-use-before-define
const [payment] = reallocate(
harden({
purses: [purse],
newPurseBalances: [newPurseBalance],
newPaymentBalances: [amount],
}),
);
// Move the withdrawn assets from this purse into a new payment
// which is returned. Total assets must remain conserved.
currentBalance = newPurseBalance;
paymentLedger.init(payment, amount);
return payment;
},
getCurrentAmount: () => purseLedger.get(purse),
getCurrentAmount: () => currentBalance,
getAllegedBrand: () => brand,
// eslint-disable-next-line no-use-before-define
getDepositFacet: () => depositFacet,
Expand All @@ -145,25 +133,20 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
return purse;
});

purseLedger = makePurseWeakStore();

const { add } = amountMath;
const empty = amountMath.getEmpty();

// Amount in circulation remains constant with reallocate.
const reallocate = ({
purses = [],
payments = [],
newPurseBalances = [],
newPaymentBalances = [],
}) => {
// There may be zero or one purse and no more. No methods pass in
// more than one purse.
assert(
purses.length === 0 || purses.length === 1,
'purses length must be 0 or 1',
);

/**
* Reallocate assets from the `payments` passed in to new payments
* created and returned, with balances from `newPaymentBalances`.
* Enforces that total assets are conserved.
*
* Note that this is not the only operation that reallocates assets.
* `purse.deposit` and `purse.withdraw` move assets between a purse and
* a payment, and so must also enforce conservation there.
*
* @param {Payment[]} payments
* @param {Amount[]} newPaymentBalances
* @returns {Payment[]}
*/
const reallocate = (payments, newPaymentBalances) => {
// There may be zero, one, or many payments as input to
// reallocate. We want to protect against someone passing in
// what appears to be multiple payments that turn out to actually
Expand All @@ -182,25 +165,15 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
});
}

assert(
purses.length === newPurseBalances.length,
details`purses and newPurseBalances should have same length`,
);

const totalPursesB = purses.map(purseLedger.get).reduce(add, empty);
const totalPaymentsB = payments.map(paymentLedger.get).reduce(add, empty);
const total = amountMath.add(totalPursesB, totalPaymentsB);
const total = payments.map(paymentLedger.get).reduce(add, empty);

const newPursesTotal = newPurseBalances.reduce(add, empty);
const newPaymentsTotal = newPaymentBalances.reduce(add, empty);
const newTotal = amountMath.add(newPaymentsTotal, newPursesTotal);
const newTotal = newPaymentBalances.reduce(add, empty);

// Invariant check
assert(amountMath.isEqual(total, newTotal), 'rights were not conserved');

// commit point
payments.forEach(payment => paymentLedger.delete(payment));
purses.forEach((purse, i) => purseLedger.set(purse, newPurseBalances[i]));

const newPayments = newPaymentBalances.map(balance => {
const newPayment = makePayment();
Expand All @@ -219,11 +192,7 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
getBrand: () => brand,
getAllegedName: () => allegedName,
getAmountMathKind: () => amountMathKind,
makeEmptyPurse: () => {
const purse = makePurse();
purseLedger.init(purse, amountMath.getEmpty());
return purse;
},
makeEmptyPurse: makePurse,

isLive: paymentP => {
return E.when(paymentP, payment => {
Expand Down Expand Up @@ -253,12 +222,7 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
const srcPaymentBalance = paymentLedger.get(srcPayment);
assertAmountEqual(srcPaymentBalance, optAmount);
// Commit point.
const [payment] = reallocate(
harden({
payments: [srcPayment],
newPaymentBalances: [srcPaymentBalance],
}),
);
const [payment] = reallocate([srcPayment], [srcPaymentBalance]);
return payment;
});
},
Expand All @@ -272,12 +236,9 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
.reduce(add, empty);
assertAmountEqual(totalPaymentsBalance, optTotalAmount);
// Commit point.
const [payment] = reallocate(
harden({
payments: fromPaymentsArray,
newPaymentBalances: [totalPaymentsBalance],
}),
);
const [payment] = reallocate(fromPaymentsArray, [
totalPaymentsBalance,
]);
return payment;
});
},
Expand All @@ -293,10 +254,8 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
);
// Commit point
const newPayments = reallocate(
harden({
payments: [srcPayment],
newPaymentBalances: [paymentAmountA, paymentAmountB],
}),
[srcPayment],
[paymentAmountA, paymentAmountB],
);
return newPayments;
});
Expand All @@ -306,12 +265,7 @@ function makeIssuerKit(allegedName, amountMathKind = MathKind.NAT) {
assertKnownPayment(srcPayment);
amounts = amounts.map(amountMath.coerce);
// Commit point
const newPayments = reallocate(
harden({
payments: [srcPayment],
newPaymentBalances: amounts,
}),
);
const newPayments = reallocate([srcPayment], amounts);
return newPayments;
});
},
Expand Down

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