Calculate position health

safe price = max(priceE8 - confidenceE8, 0)
collateral value = collateral raw × safe price × 10^6 / (10^decimals × 10^8)

const BPS = 10_000n;
const USD_SCALE = 1_000_000n;
const PRICE_SCALE = 100_000_000n;

export function ceilDiv(numerator: bigint, denominator: bigint) {
  if (denominator <= 0n) throw new Error("denominator must be positive");
  return (numerator + denominator - 1n) / denominator;
}

export function conservativeCollateralValueUsd6(input: {
  collateralRaw: bigint;
  collateralDecimals: number;
  priceE8: bigint;
  confidenceE8: bigint;
}) {
  const safePriceE8 = input.priceE8 > input.confidenceE8
    ? input.priceE8 - input.confidenceE8
    : 0n;
  const tokenScale = 10n ** BigInt(input.collateralDecimals);
  const valueUsd6 = input.collateralRaw * safePriceE8 * USD_SCALE
    / (tokenScale * PRICE_SCALE);
  return { safePriceE8, valueUsd6 };
}

export function positionRisk(input: {
  collateralValueUsd6: bigint;
  projectedDebtNusd6: bigint;
  borrowLtvBps: bigint;
  liquidationThresholdBps: bigint;
}) {
  const debt = input.projectedDebtNusd6;
  const borrowLimitNusd6 = input.collateralValueUsd6 * input.borrowLtvBps / BPS;
  const liquidationLimitNusd6 = input.collateralValueUsd6
    * input.liquidationThresholdBps / BPS;
  const currentLtvBps = input.collateralValueUsd6 === 0n
    ? null
    : debt * BPS / input.collateralValueUsd6;
  const healthFactorBps = debt === 0n
    ? null
    : liquidationLimitNusd6 * BPS / debt;

  return {
    borrowLimitNusd6,
    liquidationLimitNusd6,
    currentLtvBps,
    healthFactorBps,
    availableToMintNusd6: borrowLimitNusd6 > debt ? borrowLimitNusd6 - debt : 0n,
    liquidatable: debt > liquidationLimitNusd6,
  };
}

export function liquidationSafePriceE8(input: {
  collateralRaw: bigint;
  collateralDecimals: number;
  projectedDebtNusd6: bigint;
  liquidationThresholdBps: bigint;
}) {
  if (input.projectedDebtNusd6 === 0n) return null;
  if (input.collateralRaw === 0n) return 0n;
  const requiredValueUsd6 = ceilDiv(input.projectedDebtNusd6 * BPS, input.liquidationThresholdBps);
  return ceilDiv(
    requiredValueUsd6 * 10n ** BigInt(input.collateralDecimals) * PRICE_SCALE,
    input.collateralRaw * USD_SCALE,
  );
}

export function maximumWithdrawRaw(input: {
  collateralRaw: bigint;
  collateralValueUsd6: bigint;
  projectedDebtNusd6: bigint;
  borrowLtvBps: bigint;
}) {
  if (input.projectedDebtNusd6 === 0n) return input.collateralRaw;
  if (input.collateralRaw === 0n || input.collateralValueUsd6 === 0n) return 0n;

  // The contract requires the remaining position to stay inside borrow LTV.
  const requiredValueUsd6 = ceilDiv(input.projectedDebtNusd6 * BPS, input.borrowLtvBps);
  if (requiredValueUsd6 >= input.collateralValueUsd6) return 0n;
  const requiredCollateralRaw = ceilDiv(
    input.collateralRaw * requiredValueUsd6,
    input.collateralValueUsd6,
  );
  return input.collateralRaw > requiredCollateralRaw
    ? input.collateralRaw - requiredCollateralRaw
    : 0n;
}

import { PublicKey } from "@solana/web3.js";
import { borrowVaultPda, marketBySymbol, oraclePda, type NestClient } from "../nest-client";

export async function readHealthInputs(client: NestClient, symbol: string) {
  const market = marketBySymbol(client, symbol);
  const coreProgram = new PublicKey(client.deployment.programs.nestCore);
  const configKey = new PublicKey(market.collateralConfig);
  const vaultKey = borrowVaultPda(coreProgram, client.wallet.publicKey, configKey);
  const oracleKey = oraclePda(coreProgram, configKey);

  const [config, vault, oracle] = await Promise.all([
    client.core.account.collateralConfig.fetch(configKey),
    client.core.account.vault.fetch(vaultKey),
    client.core.account.oracleSnapshot.fetch(oracleKey),
  ]);

  return {
    config,
    vault,
    oracle,
    collateralRaw: BigInt(vault.collateralRaw.toString()),
    storedDebtNusd6: BigInt(vault.principalDebt.toString())
      + BigInt(vault.accruedFee.toString()),
    priceE8: BigInt(oracle.xstockUsd.priceE8.toString()),
    confidenceE8: BigInt(oracle.xstockUsd.confidenceE8.toString()),
  };
}