@dahlia-labs/stableswap-sdk/src/calculator/price.ts

SDK for Mobius's StableSwap program.

import { Price, TEN, TokenAmount } from "@dahlia-labs/token-utils";
import JSBI from "jsbi";

import type { IExchangeInfo } from "../entities";
import { calculateEstimatedSwapOutputAmount } from "./";

function min(a: JSBI, b: JSBI): JSBI {
  return JSBI.greaterThanOrEqual(a, b) ? b : a;
}

function max(a: JSBI, b: JSBI): JSBI {
  return JSBI.greaterThanOrEqual(a, b) ? a : b;
}

/**
 * Gets the price of the second token in the swap, i.e. "Token 1", with respect to "Token 0".
 *
 * To get the price of "Token 0", use `.invert()` on the result of this function.
 * @returns
 */
export const calculateSwapPrice = (exchangeInfo: IExchangeInfo): Price => {
  const reserve0 = exchangeInfo.reserves[0];
  const reserve1 = exchangeInfo.reserves[1];

  // We try to get at least 16 decimal points of precision here
  // Otherwise, we attempt to swap 1% of total supply of the pool
  // or at most, $1
  const inputAmountNum = max(
    JSBI.divide(
      JSBI.BigInt(10_000_000_000_000_000),
      JSBI.exponentiate(TEN, JSBI.BigInt(18 - reserve0.token.decimals))
    ),
    min(
      JSBI.exponentiate(TEN, JSBI.BigInt(reserve0.token.decimals)),
      reserve0.divide(100).quotient
    )
  );

  const inputAmount = new TokenAmount(reserve0.token, inputAmountNum);
  const outputAmount = calculateEstimatedSwapOutputAmount(
    exchangeInfo,
    inputAmount
  );

  const frac = outputAmount.outputAmountBeforeFees.divide(
    inputAmount.asFraction
  );

  return new Price(
    reserve0.token,
    reserve1.token,
    frac.denominator,
    frac.numerator
  );
};