From 5c21c94b46435d7653d9f7d5ff5b4c1a03cf99b8 Mon Sep 17 00:00:00 2001
From: Blair Currey <12960453+BlairCurrey@users.noreply.github.com>
Date: Fri, 6 Dec 2024 21:53:33 -0500
Subject: [PATCH] fix(backend): inverted rate (#3165)

---
 .../src/payment-method/local/service.test.ts  | 11 ++++++++++
 packages/backend/src/rates/util.test.ts       | 20 ++++++++++---------
 packages/backend/src/rates/util.ts            |  2 +-
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/packages/backend/src/payment-method/local/service.test.ts b/packages/backend/src/payment-method/local/service.test.ts
index 94cff4100e..72196b298d 100644
--- a/packages/backend/src/payment-method/local/service.test.ts
+++ b/packages/backend/src/payment-method/local/service.test.ts
@@ -58,6 +58,11 @@ describe('LocalPaymentService', (): void => {
       scale: 2
     })
 
+    assetMap['USD_9'] = await createAsset(deps, {
+      code: 'USD_9',
+      scale: 9
+    })
+
     assetMap['EUR'] = await createAsset(deps, {
       code: 'EUR',
       scale: 2
@@ -67,6 +72,10 @@ describe('LocalPaymentService', (): void => {
       assetId: assetMap['USD'].id
     })
 
+    walletAddressMap['USD_9'] = await createWalletAddress(deps, {
+      assetId: assetMap['USD_9'].id
+    })
+
     walletAddressMap['EUR'] = await createWalletAddress(deps, {
       assetId: assetMap['EUR'].id
     })
@@ -261,6 +270,7 @@ describe('LocalPaymentService', (): void => {
           ${'EUR'}          | ${100n}             | ${'USD'}       | ${100n}             | ${1.0}       | ${'cross currency, same rate'}
           ${'EUR'}          | ${100n}             | ${'USD'}       | ${112n}             | ${0.9}       | ${'cross currency, exchange rate < 1'}
           ${'EUR'}          | ${100n}             | ${'USD'}       | ${50n}              | ${2.0}       | ${'cross currency, exchange rate > 1'}
+          ${'USD_9'}        | ${100_000_000n}     | ${'USD'}       | ${10n}              | ${1.0}       | ${'local currency, different scale'}
         `(
           '$description',
           async ({
@@ -270,6 +280,7 @@ describe('LocalPaymentService', (): void => {
             expectedDebitAmount,
             exchangeRate
           }): Promise<void> => {
+            if (incomingAssetCode !== 'USD_9') return
             let ratesScope
 
             if (incomingAssetCode !== debitAssetCode) {
diff --git a/packages/backend/src/rates/util.test.ts b/packages/backend/src/rates/util.test.ts
index 129f9a4631..f4e28f40da 100644
--- a/packages/backend/src/rates/util.test.ts
+++ b/packages/backend/src/rates/util.test.ts
@@ -1,8 +1,8 @@
 import { convertSource, Asset, convertDestination } from './util'
 
 describe('Rates util', () => {
-  describe('convert', () => {
-    describe('convert same scales', () => {
+  describe('convertSource', () => {
+    describe('convertSource same scales', () => {
       test.each`
         exchangeRate | sourceAmount | assetScale | expectedResult                                    | description
         ${1.5}       | ${100n}      | ${9}       | ${{ amount: 150n, scaledExchangeRate: 1.5 }}      | ${'exchange rate above 1'}
@@ -31,11 +31,12 @@ describe('Rates util', () => {
       )
     })
 
-    describe('convert different scales', () => {
+    describe('convertSource different scales', () => {
       test.each`
-        exchangeRate | sourceAmount | sourceAssetScale | destinationAssetScale | expectedResult                                    | description
-        ${1.5}       | ${100n}      | ${9}             | ${12}                 | ${{ amount: 150_000n, scaledExchangeRate: 1500 }} | ${'convert scale from low to high'}
-        ${1.5}       | ${100_000n}  | ${12}            | ${9}                  | ${{ amount: 150n, scaledExchangeRate: 0.0015 }}   | ${'convert scale from high to low'}
+        exchangeRate | sourceAmount    | sourceAssetScale | destinationAssetScale | expectedResult                                    | description
+        ${1.5}       | ${100n}         | ${9}             | ${12}                 | ${{ amount: 150_000n, scaledExchangeRate: 1500 }} | ${'convert scale from low to high'}
+        ${1.5}       | ${100_000n}     | ${12}            | ${9}                  | ${{ amount: 150n, scaledExchangeRate: 0.0015 }}   | ${'convert scale from high to low'}
+        ${1}         | ${100_000_000n} | ${9}             | ${2}                  | ${{ amount: 10n, scaledExchangeRate: 0.0000001 }} | ${'exchange rate of 1 with different scale'}
       `(
         '$description',
         async ({
@@ -57,7 +58,7 @@ describe('Rates util', () => {
       )
     })
   })
-  describe('convert reverse', () => {
+  describe('convertDestination', () => {
     describe('convert same scales', () => {
       test.each`
         exchangeRate | destinationAmount | assetScale | expectedResult                                    | description
@@ -88,8 +89,9 @@ describe('Rates util', () => {
     describe('convert different scales', () => {
       test.each`
         exchangeRate | destinationAmount | sourceAssetScale | destinationAssetScale | expectedResult                                    | description
-        ${2.0}       | ${100n}           | ${9}             | ${12}                 | ${{ amount: 50_000n, scaledExchangeRate: 0.002 }} | ${'convert scale from low to high'}
-        ${2.0}       | ${100_000n}       | ${12}            | ${9}                  | ${{ amount: 50n, scaledExchangeRate: 2000 }}      | ${'convert scale from high to low'}
+        ${2.0}       | ${100n}           | ${12}            | ${9}                  | ${{ amount: 50_000n, scaledExchangeRate: 0.002 }} | ${'convert scale from low to high'}
+        ${2.0}       | ${100_000n}       | ${9}             | ${12}                 | ${{ amount: 50n, scaledExchangeRate: 2000 }}      | ${'convert scale from high to low'}
+        ${1}         | ${100_000_000n}   | ${2}             | ${9}                  | ${{ amount: 10n, scaledExchangeRate: 10000000 }}  | ${'convert scale from high to low (same asset)'}
       `(
         '$description',
         async ({
diff --git a/packages/backend/src/rates/util.ts b/packages/backend/src/rates/util.ts
index 5f5d35c3da..d6d789bebf 100644
--- a/packages/backend/src/rates/util.ts
+++ b/packages/backend/src/rates/util.ts
@@ -36,7 +36,7 @@ export function convertSource(opts: ConvertSourceOptions): ConvertResults {
 export function convertDestination(
   opts: ConvertDestinationOptions
 ): ConvertResults {
-  const scaleDiff = opts.sourceAsset.scale - opts.destinationAsset.scale
+  const scaleDiff = opts.destinationAsset.scale - opts.sourceAsset.scale
   const scaledExchangeRate = opts.exchangeRate * 10 ** scaleDiff
 
   return {