fix: count brokerage cash once and skip short-position return percent (WealthLedger/backend#140)

src/modules/investments/brokerage-accounts/brokerage-accounts.service.ts

@@ -19,6 +19,7 @@ import {
 } from './brokerage-account.dto';
 
 const PERCENT_DECIMAL_PLACES = 2;
+const ZERO_QUANTITY = 0n;
 
 function unrealizedReturns(positions: PortfolioPositionDto[]): UnrealizedReturnDto[] {
   // Cash-like CURRENCY positions must not duplicate the separately returned cash balances.
@@ -47,6 +48,13 @@ function unrealizedReturns(positions: PortfolioPositionDto[]): UnrealizedReturnD
       return money ? [money.currency] : [];
     }),
   );
+  // A short position has negative cost basis, so a percent would flip sign or net out.
+  const withShorts = new Set(
+    investments.flatMap((position) => {
+      const money = position.absoluteReturn ?? position.averagePurchasePrice ?? position.currentValue;
+      return money && decimalFromString(position.quantity).value < ZERO_QUANTITY ? [money.currency] : [];
+    }),
+  );
   const currencies = new Set([...absolute, ...costs].map((money) => money.currency));
   return [...new Set([...currencies, ...partial])]
     .sort((left, right) => left.localeCompare(right))
@@ -58,7 +66,7 @@ function unrealizedReturns(positions: PortfolioPositionDto[]): UnrealizedReturnD
         currency,
         absolute: absoluteReturn,
         costBasis,
-        percent: isZero(cost)
+        percent: isZero(cost) || withShorts.has(currency)
           ? null
           : formatDecimal(divide(
               multiply(decimalFromString(absoluteReturn), decimalFromString('100')),