From 05316bb34b327c6f3f63b4b60387faccf1ff888e Mon Sep 17 00:00:00 2001
From: Rudy Celekli <rudy@gradiahq.com>
Date: Sat, 24 Oct 2026 00:24:43 -0400
Subject: [PATCH] fix(cockpit): read a rounded-north destination heading as 000

359.6 degrees was shown as 360 degrees on the destination bearing while the compass tape uses 000.
---
 src/cockpitMath.js           | 9 +++++++++
 src/cockpitMath.test.mjs     | 9 +++++++++
 src/ui/cockpitInstruments.js | 3 ++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/cockpitMath.js b/src/cockpitMath.js
index 62015bb70..888c33ead 100644
--- a/src/cockpitMath.js
+++ b/src/cockpitMath.js
@@ -6,6 +6,15 @@ export function normalizeHeading(value) {
   return ((value % 360) + 360) % 360;
 }
 
+/**
+ * Three-digit heading readout, 000–359.
+ * Rounding 359.5° and above lands on north (000), not 360.
+ */
+export function formatHeadingReadout(degrees) {
+  if (!Number.isFinite(degrees)) return '---';
+  return String(Math.round(normalizeHeading(degrees)) % 360).padStart(3, '0');
+}
+
 /** Advance a displayed heading along the shortest arc without exceeding a slew rate. */
 export function slewHeading(current, target, maxStepDeg) {
   const from = normalizeHeading(current);
diff --git a/src/cockpitMath.test.mjs b/src/cockpitMath.test.mjs
index 2189ca35e..e49b91a57 100644
--- a/src/cockpitMath.test.mjs
+++ b/src/cockpitMath.test.mjs
@@ -15,6 +15,7 @@ import {
   formatCockpitContextScope,
   formatCockpitEmergency,
   formatCompassDivision,
+  formatHeadingReadout,
   formatSpeedRulerTick,
   normalizeHeading,
   relativeBearing,
@@ -155,6 +156,14 @@ test('compass labels use cardinals where exact and degrees elsewhere', () => {
   assert.equal(formatCompassDivision(30), '030');
 });
 
+test('a heading that rounds to north reads 000, not 360', () => {
+  assert.equal(formatHeadingReadout(359.6), '000');
+  assert.equal(formatHeadingReadout(359.4), '359');
+  assert.equal(formatHeadingReadout(0), '000');
+  assert.equal(formatHeadingReadout(10.2), '010');
+  assert.equal(formatHeadingReadout(Number.NaN), '---');
+});
+
 test('great-circle bearing resolves cardinal directions', () => {
   assert.ok(Math.abs(bearingBetweenCoordinates(0, 0, 1, 0) - 0) < 0.001);
   assert.ok(Math.abs(bearingBetweenCoordinates(0, 0, 0, 1) - 90) < 0.001);
diff --git a/src/ui/cockpitInstruments.js b/src/ui/cockpitInstruments.js
index 1904b6cea..77a4bea7d 100644
--- a/src/ui/cockpitInstruments.js
+++ b/src/ui/cockpitInstruments.js
@@ -14,6 +14,7 @@ import {
   formatAltitudeRulerTick,
   formatCompassDivision,
   formatCockpitEmergency,
+  formatHeadingReadout,
   formatSpeedRulerTick,
   normalizeHeading,
   relativeBearing,
@@ -238,7 +239,7 @@ export function updateRoute(info) {
   }
   if (this.routeDirectionLabel) {
     this.routeDirectionLabel.textContent = t('DEST {bearing}', {
-      bearing: `${String(Math.round(destinationBearing)).padStart(3, '0')}°`,
+      bearing: `${formatHeadingReadout(destinationBearing)}°`,
     });
   }
 }