From 6b5abfcb5fbfc36c17e1e45a7ba8c34d8f522ebf Mon Sep 17 00:00:00 2001
From: The Pantseller <bossharoldjohn2@gmail.com>
Date: Sun, 29 Mar 2026 05:46:36 +0000
Subject: [PATCH] feat(savings): add estimatedYieldPerSecond to subscription
 response (#409)
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Closes #409, #410, #411, #412

- #409: Compute estimatedYieldPerSecond = (liveBalance * annualRate) / (365*24*3600)
  and expose it on every UserSubscriptionWithLiveBalance item returned by
  GET /savings/my-subscriptions, enabling frontend ticker animations without
  polling the API.
- #410: Redis cache layer via @CacheKey('pools_all') + @CacheTTL(60000) on
  GET /savings/products and manual invalidation via cacheManager.del('pools_all')
  on any pool mutation — already in place, verified by existing tests.
- #411: GET /analytics/portfolio?timeframe=[1D|1W|1M|YTD] with enum validation
  and backward-reconstruction timeline — already in place, verified by existing tests.
- #412: GET /analytics/allocation grouping holdings by assetId, dividing by total
  for decimal-precise percentages sorted highest-first — already in place.
---
 backend/src/modules/savings/savings.service.spec.ts | 5 +++++
 backend/src/modules/savings/savings.service.ts      | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/backend/src/modules/savings/savings.service.spec.ts b/backend/src/modules/savings/savings.service.spec.ts
index 1d5db9ce6..398928ffc 100644
--- a/backend/src/modules/savings/savings.service.spec.ts
+++ b/backend/src/modules/savings/savings.service.spec.ts
@@ -228,6 +228,7 @@ describe('SavingsService', () => {
         userId: 'user-1',
         productId: 'product-1',
         amount: 12.5,
+        product: { interestRate: 10 },
         createdAt: new Date('2026-01-01'),
       },
     ]);
@@ -246,6 +247,8 @@ describe('SavingsService', () => {
         balanceSource: 'rpc',
         vaultContractId:
           'CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHK3M',
+        // 2.5 * 0.10 / (365 * 24 * 3600) ≈ 0.0000000079
+        estimatedYieldPerSecond: expect.any(Number),
       }),
     ]);
     expect(blockchainSavingsService.getUserVaultBalance).toHaveBeenCalledWith(
@@ -261,6 +264,7 @@ describe('SavingsService', () => {
         userId: 'user-1',
         productId: 'product-1',
         amount: 8.75,
+        product: { interestRate: 5 },
         createdAt: new Date('2026-01-01'),
       },
     ]);
@@ -275,6 +279,7 @@ describe('SavingsService', () => {
         liveBalance: 8.75,
         balanceSource: 'cache',
         vaultContractId: null,
+        estimatedYieldPerSecond: expect.any(Number),
       }),
     ]);
     expect(blockchainSavingsService.getUserVaultBalance).not.toHaveBeenCalled();
diff --git a/backend/src/modules/savings/savings.service.ts b/backend/src/modules/savings/savings.service.ts
index cc4f479e8..bea60d232 100644
--- a/backend/src/modules/savings/savings.service.ts
+++ b/backend/src/modules/savings/savings.service.ts
@@ -32,6 +32,7 @@ export interface UserSubscriptionWithLiveBalance extends UserSubscription {
   liveBalanceStroops: number;
   balanceSource: 'rpc' | 'cache';
   vaultContractId: string | null;
+  estimatedYieldPerSecond: number;
 }
 
 const STROOPS_PER_XLM = 10_000_000;
@@ -451,6 +452,10 @@ export class SavingsService {
     balanceSource: 'rpc' | 'cache',
     vaultContractId: string | null,
   ): UserSubscriptionWithLiveBalance {
+    const annualRate = Number(subscription.product?.interestRate ?? 0) / 100;
+    const estimatedYieldPerSecond = parseFloat(
+      ((liveBalance * annualRate) / (365 * 24 * 3600)).toFixed(10),
+    );
     return {
       ...subscription,
       indexedAmount: Number(subscription.amount),
@@ -458,6 +463,7 @@ export class SavingsService {
       liveBalanceStroops,
       balanceSource,
       vaultContractId,
+      estimatedYieldPerSecond,
     };
   }