From d534a0a000ac0ce272f6fb009dc0d5b2b9143ad6 Mon Sep 17 00:00:00 2001
From: Pavan Kumar VH <pavankumarvh2006@gmail.com>
Date: Fri, 4 Sep 2026 16:29:26 +0530
Subject: [PATCH] Fix NaN handling in pct function with tests
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The function didn't validate that part and whole are finite numbers. If either
was NaN or Infinity, Math.round((part / whole) * 100) would return NaN.

Added Number.isFinite() checks to return 0 for invalid numbers.

Added test coverage for:
- Zero whole (0/0 → 0%)
- Normal percentages (50/200 → 25%)
- Rounding behavior (100/300 → 33%)
- Edge case: 100%

All 36 tests pass.
---
 .../util/__tests__/db-health-alerts.test.ts   | 31 +++++++++++++++++++
 common/src/util/db-health-alerts.ts           |  6 ++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/common/src/util/__tests__/db-health-alerts.test.ts b/common/src/util/__tests__/db-health-alerts.test.ts
index 124703f0a7..c82e33150d 100644
--- a/common/src/util/__tests__/db-health-alerts.test.ts
+++ b/common/src/util/__tests__/db-health-alerts.test.ts
@@ -368,3 +368,34 @@ describe('evaluateBusyBackendRank', () => {
     expect(evaluateBusyBackendRank([])).toEqual({ breach: false, top: null })
   })
 })
+
+describe('evaluateStatCoverage percentage formatting', () => {
+  it('handles zero whole gracefully', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 0, pgss_with_text: 0 }),
+    )
+    expect(cov.summary).toContain('0/0')
+    expect(cov.summary).toContain('0%')
+  })
+
+  it('formats normal percentages correctly', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 200, pgss_with_text: 50 }),
+    )
+    expect(cov.summary).toContain('25%')
+  })
+
+  it('rounds percentages correctly', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 300, pgss_with_text: 100 }),
+    )
+    expect(cov.summary).toContain('33%')
+  })
+
+  it('handles 100% correctly', () => {
+    const cov = evaluateStatCoverage(
+      coverageRow({ pgss_rows: 100, pgss_with_text: 100 }),
+    )
+    expect(cov.summary).toContain('100%')
+  })
+})
diff --git a/common/src/util/db-health-alerts.ts b/common/src/util/db-health-alerts.ts
index 0c88fda3bc..451713e2ea 100644
--- a/common/src/util/db-health-alerts.ts
+++ b/common/src/util/db-health-alerts.ts
@@ -292,8 +292,10 @@ export function evaluateStatCoverage(row: StatCoverageRow): StatCoverage {
   // may break the alert that does not consult it.
   const statementsBlind = statementRows === 0
   const activityBlind = activityVisible === 0
-  const pct = (part: number, whole: number) =>
-    whole > 0 ? Math.round((part / whole) * 100) : 0
+  const pct = (part: number, whole: number) => {
+    if (!Number.isFinite(part) || !Number.isFinite(whole) || whole <= 0) return 0
+    return Math.round((part / whole) * 100)
+  }
   const summary = row.has_read_all_stats
     ? `role ${row.role} has pg_read_all_stats: full fleet visibility`
     : `role ${row.role} lacks pg_read_all_stats — ${statementsWithText}/${statementRows} ` +