sdk: add calculateBaseAssetAmountToCoverMarginShortage

Author: crispheaney

sdk/src/constants/numericConstants.ts

@@ -84,6 +84,9 @@ export const MARGIN_PRECISION = TEN_THOUSAND;
 export const BID_ASK_SPREAD_PRECISION = new BN(1000000); // 10^6
 export const LIQUIDATION_PCT_PRECISION = TEN_THOUSAND;
 export const FUNDING_RATE_OFFSET_DENOMINATOR = new BN(5000);
+export const PRICE_TIMES_AMM_TO_QUOTE_PRECISION_RATIO = PRICE_PRECISION.mul(
+	AMM_TO_QUOTE_PRECISION_RATIO
+);
 
 export const FIVE_MINUTE = new BN(60 * 5);
 export const ONE_HOUR = new BN(60 * 60);

sdk/src/index.ts

@@ -58,6 +58,7 @@ export * from './math/amm';
 export * from './math/trade';
 export * from './math/orders';
 export * from './math/repeg';
+export * from './math/liquidation';
 export * from './math/margin';
 export * from './math/insurance';
 export * from './math/superStake';

sdk/src/math/liquidation.ts

@@ -0,0 +1,37 @@
+import { BN } from '@coral-xyz/anchor';
+import {
+	PRICE_PRECISION,
+	LIQUIDATION_FEE_PRECISION,
+	MARGIN_PRECISION,
+	PRICE_TIMES_AMM_TO_QUOTE_PRECISION_RATIO,
+} from '../constants/numericConstants';
+
+export function calculateBaseAssetAmountToCoverMarginShortage(
+	marginShortage: BN,
+	marginRatio: number,
+	liquidationFee: number,
+	ifLiquidationFee: number,
+	oraclePrice: BN,
+	quoteOraclePrice: BN
+): BN | undefined {
+	const marginRatioBN = new BN(marginRatio)
+		.mul(LIQUIDATION_FEE_PRECISION)
+		.div(MARGIN_PRECISION);
+	const liquidationFeeBN = new BN(liquidationFee);
+
+	if (oraclePrice.eq(new BN(0)) || marginRatioBN.lte(liquidationFeeBN)) {
+		// undefined is max
+		return undefined;
+	}
+
+	return marginShortage.mul(PRICE_TIMES_AMM_TO_QUOTE_PRECISION_RATIO).div(
+		oraclePrice
+			.mul(quoteOraclePrice)
+			.div(PRICE_PRECISION)
+			.mul(marginRatioBN.sub(liquidationFeeBN))
+			.div(LIQUIDATION_FEE_PRECISION)
+			.sub(
+				oraclePrice.mul(new BN(ifLiquidationFee)).div(LIQUIDATION_FEE_PRECISION)
+			)
+	);
+}