fix: keep antimeridian traffic requests in range

CHANGELOG.md

@@ -267,6 +267,10 @@ of current runtime behavior, see [`docs/CURRENT-STATE.md`](docs/CURRENT-STATE.md
 
 ### Fixed
 
+- Keep traffic-road bounds crossing the antimeridian monotonic and inside the
+  longitude range accepted by the Overpass request path, preserving the small
+  wrapped span instead of producing an inverted or rejected box (#392 — thanks
+  @Ashfaqbs).
 - Make `npm run doctor` report keyless anonymous OpenSky access for explicit
   `OPENSKY_AUTH_MODE=anon` and OAuth mode without a client pair, retain the
   existing OAuth-pair capability wording, and identify selected Basic or auto

src/data/trafficBounds.js

@@ -139,19 +139,35 @@ function longitudeSpanDeg(west, east) {
   return raw >= 0 ? raw : raw + 360;
 }
 
+/** Keep a monotonic longitude range inside the traffic source's legal domain. */
+function boundedLongitudeRange(center, span) {
+  let west = center - span / 2;
+  let east = center + span / 2;
+  if (east > 180) {
+    west -= east - 180;
+    east = 180;
+  }
+  if (west < -180) {
+    east += -180 - west;
+    west = -180;
+  }
+  return { west, east };
+}
+
 /**
  * Clamp a bounding box's spans to `maxSpanDeg` and recenter it on `center`.
  *
  * Preserves the pre-C4 span semantics (each axis capped at 0.05° ≈ 5.5 km)
  * but centers the box on the derived look-at point instead of the view
- * rectangle's midpoint. Idempotent when `center` is the box's own midpoint.
+ * rectangle's midpoint. At the antimeridian the whole box shifts just far
+ * enough to remain inside [-180, 180], because the road source accepts one
+ * monotonic Overpass bounding box. Idempotent when `center` is the box's own
+ * midpoint.
  *
  * Longitude is handled as a cyclic axis for the span calculation, so the
- * input span wraps correctly across the antimeridian. The output west/east
- * are deliberately left unnormalized (may fall outside [-180, 180)) so that
- * `west <= east` always holds — callers such as `getBoundsCenter` and
- * `boundsOverlap` rely on that invariant and would silently misbehave on a
- * normalized-but-inverted box (see #392 review).
+ * input span wraps correctly across the antimeridian. Output remains
+ * monotonic because callers such as `getBoundsCenter` and `boundsOverlap`
+ * rely on `west <= east`.
  *
  * @param {{south:number, west:number, north:number, east:number}} bounds
  *   Source bounds (span donor).
@@ -161,11 +177,14 @@ function longitudeSpanDeg(west, east) {
  */
 export function clampBoundsAroundCenter(bounds, center, maxSpanDeg = 0.05) {
   const latSpan = Math.min(bounds.north - bounds.south, maxSpanDeg);
-  const lonSpan = Math.min(longitudeSpanDeg(bounds.west, bounds.east), maxSpanDeg);
+  const lonSpan = Math.min(
+    longitudeSpanDeg(bounds.west, bounds.east),
+    maxSpanDeg,
+  );
+  const longitude = boundedLongitudeRange(center.lon, lonSpan);
   return {
     south: center.lat - latSpan / 2,
     north: center.lat + latSpan / 2,
-    west: center.lon - lonSpan / 2,
-    east: center.lon + lonSpan / 2,
+    ...longitude,
   };
 }

src/data/trafficBounds.test.mjs

@@ -109,30 +109,18 @@ test('span clamp is idempotent on already-clamped bounds (loadRoadsForBounds re-
   assert.deepEqual(twice, once);
 });
 
-test('span clamp handles bounds crossing the antimeridian', () => {
-  const bounds = {
-    south: -0.02,
-    north: 0.02,
-    west: 179.98,
-    east: -179.98,
-  };
+test('span clamp keeps antimeridian bounds monotonic and request-safe', () => {
+  for (const centerLon of [179.99, -179.99]) {
+    const result = clampBoundsAroundCenter({
+      south: -0.02,
+      north: 0.02,
+      west: 179.98,
+      east: -179.98,
+    }, { lat: 0, lon: centerLon }, 0.05);
 
-  const center = {
-    lat: 0,
-    lon: 179.99,
-  };
-
-  const result = clampBoundsAroundCenter(bounds, center, 0.05);
-
-  // west/east are deliberately left unnormalized (may exceed 180) so that
-  // west <= east always holds for downstream consumers (getBoundsCenter,
-  // boundsOverlap) that assume a monotonic box. See #392 review.
-  assert.ok(result.west <= result.east, `west/east not monotonic: ${result.west}, ${result.east}`);
-  assert.ok(Math.abs(result.east - result.west - 0.04) < 1e-12);
-
-  // The plain-mean center a caller like getBoundsCenter computes must land
-  // back on the antimeridian near the requested center, not ~180 degrees
-  // away on the opposite side of the planet.
-  const center2 = (result.west + result.east) / 2;
-  assert.ok(Math.abs(center2 - center.lon) < 1e-9, `center drifted: ${center2}`);
+    assert.ok(result.west >= -180 && result.east <= 180);
+    assert.ok(result.west <= result.east, `west/east not monotonic: ${result.west}, ${result.east}`);
+    assert.ok(Math.abs(result.east - result.west - 0.04) < 1e-12);
+    assert.ok(result.west <= centerLon && centerLon <= result.east);
+  }
 });

src/layers/traffic/source.test.mjs

@@ -2,6 +2,7 @@ import assert from 'node:assert/strict';
 import test from 'node:test';
 import { readFileSync } from 'node:fs';
 import { createTrafficSource } from './source.js';
+import { clampBoundsAroundCenter } from '../../data/trafficBounds.js';
 const bounds = { south: 30.267, west: -97.744, north: 30.268, east: -97.743 };
 const fixture = readFileSync(
   new URL(
@@ -87,6 +88,28 @@ test('road requests have finite bounds and retain the two-pass query', async ()
     /residential/,
   );
 });
+test('antimeridian clamps produce road bounds accepted on either side', async () => {
+  const calls = [];
+  const source = createTrafficSource({
+    fetchImpl: async (...args) => {
+      calls.push(args);
+      return new Response('{"elements":[]}');
+    },
+  });
+  for (const centerLon of [179.99, -179.99]) {
+    const clamped = clampBoundsAroundCenter(
+      {
+        south: -0.02,
+        north: 0.02,
+        west: 179.98,
+        east: -179.98,
+      },
+      { lat: 0, lon: centerLon },
+    );
+    await source.requestRoads(clamped);
+  }
+  assert.equal(calls.length, 2);
+});
 test('malformed availability is an unavailable source rather than a keyless response', async () => {
   const source = createTrafficSource({
     fetchImpl: async () => new Response('{}'),