client-js: add JS helpers for interest bearing tokens' UIAmounts (#53)

* WIP: amount to ui amount helpers and tests

* clean up helper functions

* remove ava verbose mode

* prettier fix

* address pr comments

* pnpm format fix

* re-run formatting

clients/js/package.json

@@ -42,7 +42,8 @@
   },
   "homepage": "https://github.com/solana-program/token-2022#readme",
   "peerDependencies": {
-    "@solana/web3.js": "^2.0.0"
+    "@solana/web3.js": "^2.0.0",
+    "@solana/sysvars": "^2.0.0"
   },
   "devDependencies": {
     "@ava/typescript": "^4.1.0",

clients/js/src/amountToUiAmount.ts

@@ -0,0 +1,279 @@
+import {
+  type GetAccountInfoApi,
+  type Rpc,
+  Address,
+  UnixTimestamp,
+  unwrapOption,
+} from '@solana/web3.js';
+import { fetchSysvarClock } from '@solana/sysvars';
+import { fetchMint } from './generated';
+
+/**
+ * Calculates the exponent for the interest rate formula.
+ * @param t1 - The start time in seconds.
+ * @param t2 - The end time in seconds.
+ * @param r  - The interest rate in basis points.
+ *
+ * @returns The calculated exponent.
+ */
+function calculateExponentForTimesAndRate(t1: number, t2: number, r: number) {
+  const ONE_IN_BASIS_POINTS = 10000;
+  const SECONDS_PER_YEAR = 60 * 60 * 24 * 365.24;
+  const timespan = t2 - t1;
+  if (timespan < 0) {
+    throw new Error('Invalid timespan: end time before start time');
+  }
+
+  const numerator = r * timespan;
+  const exponent = numerator / (SECONDS_PER_YEAR * ONE_IN_BASIS_POINTS);
+  return Math.exp(exponent);
+}
+
+/**
+ * Calculates the total scale factor for an interest bearing token by combining two exponential functions:
+ * One for the period between initialization and last update using the pre-update average rate,
+ * and another for the period between last update and current time using the current rate.
+ *
+ * @param currentTimestamp         Current timestamp in seconds
+ * @param lastUpdateTimestamp      Last time the interest rate was updated in seconds
+ * @param initializationTimestamp  Time the interest bearing extension was initialized in seconds
+ * @param preUpdateAverageRate     Interest rate in basis points before last update
+ * @param currentRate              Current interest rate in basis points
+ *
+ * @returns The total scale factor as a product of the two exponential functions
+ */
+function calculateTotalScale({
+  currentTimestamp,
+  lastUpdateTimestamp,
+  initializationTimestamp,
+  preUpdateAverageRate,
+  currentRate,
+}: {
+  currentTimestamp: number;
+  lastUpdateTimestamp: number;
+  initializationTimestamp: number;
+  preUpdateAverageRate: number;
+  currentRate: number;
+}): number {
+  // Calculate pre-update exponent
+  // e^(preUpdateAverageRate * (lastUpdateTimestamp - initializationTimestamp) / (SECONDS_PER_YEAR * ONE_IN_BASIS_POINTS))
+  const preUpdateExp = calculateExponentForTimesAndRate(
+    initializationTimestamp,
+    lastUpdateTimestamp,
+    preUpdateAverageRate
+  );
+
+  // Calculate post-update exponent
+  // e^(currentRate * (currentTimestamp - lastUpdateTimestamp) / (SECONDS_PER_YEAR * ONE_IN_BASIS_POINTS))
+  const postUpdateExp = calculateExponentForTimesAndRate(
+    lastUpdateTimestamp,
+    currentTimestamp,
+    currentRate
+  );
+
+  return preUpdateExp * postUpdateExp;
+}
+
+/**
+ * Retrieves the current timestamp from the Solana clock sysvar.
+ * @param rpc - The Solana rpc object.
+ * @returns A promise that resolves to the current timestamp in seconds.
+ * @throws An error if the sysvar clock cannot be fetched or parsed.
+ */
+async function getSysvarClockTimestamp(
+  rpc: Rpc<GetAccountInfoApi>
+): Promise<UnixTimestamp> {
+  const info = await fetchSysvarClock(rpc);
+  if (!info) {
+    throw new Error('Failed to fetch sysvar clock');
+  }
+  return info.unixTimestamp;
+}
+
+/**
+ * Convert amount to UiAmount for a mint with interest bearing extension without simulating a transaction
+ * This implements the same logic as the CPI instruction available in /token/program-2022/src/extension/interest_bearing_mint/mod.rs
+ * In general to calculate compounding interest over a period of time, the formula is:
+ * A = P * e^(r * t) where
+ * A = final amount after interest
+ * P = principal amount (initial investment)
+ * r = annual interest rate (as a decimal, e.g., 5% = 0.05)
+ * t = time in years
+ * e = mathematical constant (~2.718)
+ *
+ * In this case, we are calculating the total scale factor for the interest bearing extension which is the product of two exponential functions:
+ * totalScale = e^(r1 * t1) * e^(r2 * t2)
+ * where r1 and r2 are the interest rates before and after the last update, and t1 and t2 are the times in years between
+ * the initialization timestamp and the last update timestamp, and between the last update timestamp and the current timestamp.
+ *
+ * @param amount                   Amount of tokens to be converted
+ * @param decimals                 Number of decimals of the mint
+ * @param currentTimestamp         Current timestamp in seconds
+ * @param lastUpdateTimestamp      Last time the interest rate was updated in seconds
+ * @param initializationTimestamp  Time the interest bearing extension was initialized in seconds
+ * @param preUpdateAverageRate     Interest rate in basis points (1 basis point = 0.01%) before last update
+ * @param currentRate              Current interest rate in basis points
+ *
+ * @return Amount scaled by accrued interest as a string with appropriate decimal places
+ */
+export function amountToUiAmountForInterestBearingMintWithoutSimulation(
+  amount: bigint,
+  decimals: number,
+  currentTimestamp: number, // in seconds
+  lastUpdateTimestamp: number,
+  initializationTimestamp: number,
+  preUpdateAverageRate: number,
+  currentRate: number
+): string {
+  const totalScale = calculateTotalScale({
+    currentTimestamp,
+    lastUpdateTimestamp,
+    initializationTimestamp,
+    preUpdateAverageRate,
+    currentRate,
+  });
+  // Scale the amount by the total interest factor
+  const scaledAmount = Number(amount) * totalScale;
+
+  // Calculate the decimal factor (e.g. 100 for 2 decimals)
+  const decimalFactor = Math.pow(10, decimals);
+
+  // Convert to UI amount by:
+  // 1. Truncating to remove any remaining decimals
+  // 2. Dividing by decimal factor to get final UI amount
+  // 3. Converting to string
+  return (Math.trunc(scaledAmount) / decimalFactor).toString();
+}
+
+/**
+ * Convert amount to UiAmount for a mint without simulating a transaction
+ * This implements the same logic as `process_amount_to_ui_amount` in
+ * solana-labs/solana-program-library/token/program-2022/src/processor.rs
+ * and `process_amount_to_ui_amount` in solana-labs/solana-program-library/token/program/src/processor.rs
+ *
+ * @param rpc     Rpc to use
+ * @param mint    Mint to use for calculations
+ * @param amount  Amount of tokens to be converted to Ui Amount
+ *
+ * @return Ui Amount generated
+ */
+export async function amountToUiAmountForMintWithoutSimulation(
+  rpc: Rpc<GetAccountInfoApi>,
+  mint: Address,
+  amount: bigint
+): Promise<string> {
+  const accountInfo = await fetchMint(rpc, mint);
+  const extensions = unwrapOption(accountInfo.data.extensions);
+  const interestBearingMintConfigState = extensions?.find(
+    (ext) => ext.__kind === 'InterestBearingConfig'
+  );
+  if (!interestBearingMintConfigState) {
+    const amountNumber = Number(amount);
+    const decimalsFactor = Math.pow(10, accountInfo.data.decimals);
+    return (amountNumber / decimalsFactor).toString();
+  }
+
+  const timestamp = await getSysvarClockTimestamp(rpc);
+
+  return amountToUiAmountForInterestBearingMintWithoutSimulation(
+    amount,
+    accountInfo.data.decimals,
+    Number(timestamp),
+    Number(interestBearingMintConfigState.lastUpdateTimestamp),
+    Number(interestBearingMintConfigState.initializationTimestamp),
+    interestBearingMintConfigState.preUpdateAverageRate,
+    interestBearingMintConfigState.currentRate
+  );
+}
+
+/**
+ * Convert an amount with interest back to the original amount without interest
+ * This implements the same logic as the CPI instruction available in /token/program-2022/src/extension/interest_bearing_mint/mod.rs
+ *
+ * @param uiAmount                  UI Amount (principal plus continuously compounding interest) to be converted back to original principal
+ * @param decimals                  Number of decimals for the mint
+ * @param currentTimestamp          Current timestamp in seconds
+ * @param lastUpdateTimestamp       Last time the interest rate was updated in seconds
+ * @param initializationTimestamp   Time the interest bearing extension was initialized in seconds
+ * @param preUpdateAverageRate      Interest rate in basis points (hundredths of a percent) before the last update
+ * @param currentRate              Current interest rate in basis points
+ *
+ * In general to calculate the principal from the UI amount, the formula is:
+ * P = A / (e^(r * t)) where
+ * P = principal
+ * A = UI amount
+ * r = annual interest rate (as a decimal, e.g., 5% = 0.05)
+ * t = time in years
+ *
+ * In this case, we are calculating the principal by dividing the UI amount by the total scale factor which is the product of two exponential functions:
+ * totalScale = e^(r1 * t1) * e^(r2 * t2)
+ * where r1 is the pre-update average rate, r2 is the current rate, t1 is the time in years between the initialization timestamp and the last update timestamp,
+ * and t2 is the time in years between the last update timestamp and the current timestamp.
+ * then to calculate the principal, we divide the UI amount by the total scale factor:
+ * P = A / totalScale
+ *
+ * @return Original amount (principal) without interest
+ */
+export function uiAmountToAmountForInterestBearingMintWithoutSimulation(
+  uiAmount: string,
+  decimals: number,
+  currentTimestamp: number, // in seconds
+  lastUpdateTimestamp: number,
+  initializationTimestamp: number,
+  preUpdateAverageRate: number,
+  currentRate: number
+): bigint {
+  const uiAmountNumber = parseFloat(uiAmount);
+  const decimalsFactor = Math.pow(10, decimals);
+  const uiAmountScaled = uiAmountNumber * decimalsFactor;
+
+  const totalScale = calculateTotalScale({
+    currentTimestamp,
+    lastUpdateTimestamp,
+    initializationTimestamp,
+    preUpdateAverageRate,
+    currentRate,
+  });
+
+  // Calculate original principal by dividing the UI amount (principal + interest) by the total scale
+  const originalPrincipal = uiAmountScaled / totalScale;
+  return BigInt(Math.trunc(originalPrincipal));
+}
+
+/**
+ * Convert a UI amount back to the raw amount
+ *
+ * @param rpc      Rpc to use
+ * @param mint     Mint to use for calculations
+ * @param uiAmount UI Amount to be converted back to raw amount
+ *
+ * @return Raw amount
+ */
+export async function uiAmountToAmountForMintWithoutSimulation(
+  rpc: Rpc<GetAccountInfoApi>,
+  mint: Address,
+  uiAmount: string
+): Promise<bigint> {
+  const accountInfo = await fetchMint(rpc, mint);
+  const extensions = unwrapOption(accountInfo.data.extensions);
+  const interestBearingMintConfigState = extensions?.find(
+    (ext) => ext.__kind === 'InterestBearingConfig'
+  );
+  if (!interestBearingMintConfigState) {
+    const uiAmountScaled =
+      parseFloat(uiAmount) * Math.pow(10, accountInfo.data.decimals);
+    return BigInt(Math.trunc(uiAmountScaled));
+  }
+
+  const timestamp = await getSysvarClockTimestamp(rpc);
+
+  return uiAmountToAmountForInterestBearingMintWithoutSimulation(
+    uiAmount,
+    accountInfo.data.decimals,
+    Number(timestamp),
+    Number(interestBearingMintConfigState.lastUpdateTimestamp),
+    Number(interestBearingMintConfigState.initializationTimestamp),
+    interestBearingMintConfigState.preUpdateAverageRate,
+    interestBearingMintConfigState.currentRate
+  );
+}

clients/js/src/index.ts

@@ -1,5 +1,6 @@
 export * from './generated';
 
+export * from './amountToUiAmount';
 export * from './getInitializeInstructionsForExtensions';
 export * from './getTokenSize';
 export * from './getMintSize';