fix(backend): correct amortization schedule and total due interest ca…

backend/src/__tests__/loanEndpoints.test.ts

@@ -330,6 +330,12 @@ describe('GET /api/loans/:loanId', () => {
     expect(response.body.success).toBe(true);
     expect(response.body.loanId).toBe('123');
     expect(response.body.summary.principal).toBe(1000);
+    expect(response.body.summary.accruedInterest).toBeGreaterThan(0);
+    expect(response.body.summary.totalOwed).toBe(
+      response.body.summary.principal +
+        response.body.summary.accruedInterest -
+        response.body.summary.totalRepaid,
+    );
   });
 
   it('should return 403 when the loan belongs to another borrower', async () => {
@@ -385,6 +391,9 @@ describe('GET /api/loans/:loanId/amortization-schedule', () => {
       totalInterest: 120,
       totalDue: 1120,
     });
+    expect(response.body.amortization.totalDue).toBe(
+      response.body.amortization.principal + response.body.amortization.totalInterest,
+    );
     expect(Array.isArray(response.body.amortization.schedule)).toBe(true);
     expect(response.body.amortization.schedule.length).toBeGreaterThan(0);
   });

backend/src/controllers/loanController.ts

@@ -52,7 +52,7 @@
   try {
     const { loanId } = req.params;
 
     const borrower = (req as any).user?.publicKey as string;
 
     const result = await query('SELECT * FROM loans WHERE id = $1', [loanId]);
     const loan = result.rows[0] as Record<string, unknown> | undefined;
@@ -560,7 +560,7 @@
   const accruedInterest = isPending
     ? 0
     : (principal * rateBps * elapsedLedgers) / (10000 * termLedgers);
-  const totalOwed = principal - accruedInterest - totalRepaid;
+  const totalOwed = principal + accruedInterest - totalRepaid;
 
   res.json({
     success: true,