@agoric/zoe/src/contracts/loan/index.js

Zoe: the Smart Contract Framework for Offer Enforcement

import { Nat } from '@endo/nat';

import {
  assertIssuerKeywords,
  makeRatio,
} from '../../contractSupport/index.js';
import { makeLendInvitation } from './lend.js';

/**
 * @import {PriceAuthority, PriceDescription, PriceQuote, PriceQuoteValue, PriceQuery,} from '@agoric/zoe/tools/types.js';
 */

/**
 * Add collateral of a particular brand and get a loan of another
 * brand. Collateral (also known as margin) must be greater than the
 * loan value, at an amount set by the Maintenance Margin Requirement
 * (mmr) in the terms of the contract. The loan does not have a
 * distinct end time. Rather, if the value of the collateral changes
 * such that insufficient margin is provided, the collateral is
 * liquidated, and the loan is closed. At any time, the borrower can
 * add collateral or repay the loan with interest, closing the loan.
 * The borrower can set up their own margin calls by getting the
 * `priceAuthority` from the terms and calling
 * `E(priceAuthority).quoteWhenLT(allCollateral, x)` where x is the
 * value of the collateral in the Loan brand at which they want a
 * reminder to addCollateral.
 *
 * Note that all collateral must be of the same brand and all of the
 * loaned amount and interest must be of the same (separate) brand.
 *
 * Terms:
 *  * mmr (default = 150/100) - the Maintenance Margin Requirement, as a
 *    ratio. The default is 150/100, meaning that collateral should be
 *    worth at least 150% of the loan. If the value of the collateral
 *    drops below mmr, liquidation occurs.
 *  * priceAuthority - will be used for getting the current value of
 *    collateral and setting liquidation triggers.
 *  * autoswapInstance - The running contract instance for an Autoswap
 *    installation. The publicFacet of the
 *    instance is used for producing an invitation to sell the
 *    collateral on liquidation.
 *  * periodNotifier - the Notifier that provides notifications that
 *    periods have passed, on which compound interest will be
 *    calculated using the interestRate. Notifiers don't guarantee
 *    that clients will see all the changes, so the contract must
 *    track when interest last accrued.
 *  * interestRate - the rate in basis points that will be multiplied
 *    with the debt on every period to compound interest.
 *  * interestPeriod - the period at which interest compounds.
 *
 * IssuerKeywordRecord:
 *  * Keyword: 'Collateral' - The issuer for the digital assets to be
 *    escrowed as collateral.
 *  * Keyword: 'Loan' - The issuer for the digital assets to be loaned
 *    out.
 *
 * @param {ZCF<{
 *   mmr: Ratio,
 *   autoswapInstance: Instance,
 *   priceAuthority: PriceAuthority,
 *   periodNotifier: PeriodNotifier,
 *   interestRate: Ratio,
 *   interestPeriod: bigint,
 * }>} zcf
 */
const start = async zcf => {
  assertIssuerKeywords(zcf, harden(['Collateral', 'Loan']));

  // Rather than grabbing the terms each time we use them, let's set
  // some defaults and add them to a contract-wide config.

  const {
    autoswapInstance,
    priceAuthority,
    periodNotifier,
    interestRate,
    interestPeriod,
    brands: { Loan: loanBrand, Collateral: collateralBrand },
    mmr = makeRatio(150n, loanBrand), // Maintenance Margin Requirement
  } = zcf.getTerms();

  assert(autoswapInstance, 'autoswapInstance must be provided');
  assert(priceAuthority, 'priceAuthority must be provided');
  assert(periodNotifier, 'periodNotifier must be provided');
  Nat(interestPeriod);

  /** @type {LoanTerms} */
  const config = {
    mmr,
    autoswapInstance,
    priceAuthority,
    periodNotifier,
    interestRate,
    interestPeriod,
    loanBrand,
    collateralBrand,
  };

  const creatorInvitation = makeLendInvitation(zcf, harden(config));

  return { creatorInvitation };
};

harden(start);
export { start };