From 8ed7b8d112be5750e6edf3b53d5bbed52d840ca3 Mon Sep 17 00:00:00 2001
From: Edward Betts <edward@4angle.com>
Date: Sat, 15 Aug 2026 16:38:43 +0100
Subject: [PATCH] Reuse stops when zooming within loaded map bounds

---
 src/uk_bus_stops/static/app.js        | 32 +++++++++++----------------
 tests/test_uk_bus_stops_playwright.py |  8 +++----
 2 files changed, 17 insertions(+), 23 deletions(-)

diff --git a/src/uk_bus_stops/static/app.js b/src/uk_bus_stops/static/app.js
index 3553d18..7f49426 100644
--- a/src/uk_bus_stops/static/app.js
+++ b/src/uk_bus_stops/static/app.js
@@ -17,6 +17,7 @@ let hoveredMarkerHalo = null;
 let userMapInteractionPending = false;
 let mapMoveTimer = null;
 let mapRequestController = null;
+let loadedMapBounds = null;
 let returnToResults = false;
 let returnViaHistory = false;
 const MIN_MAP_STOP_ZOOM = 15;
@@ -167,25 +168,6 @@ async function loadSharedStop(type, id) {
     const response = await fetch(stopApiUrl(API_URLS.stopTemplate, type, id));
     const data = await response.json();
     if (!response.ok) throw new Error(data.message || 'Could not load that stop.');
-    let nearbyData = {
-      kind: 'location',
-      location: {lat: data.stop.lat, lon: data.stop.lon, label: data.stop.name},
-      stops: [data.stop],
-    };
-    try {
-      const nearbyParams = new URLSearchParams({lat: data.stop.lat, lon: data.stop.lon});
-      const nearbyResponse = await fetch(`${API_URLS.stops}?${nearbyParams}`);
-      const nearbyResult = await nearbyResponse.json();
-      if (nearbyResponse.ok) nearbyData = nearbyResult;
-    } catch (_) {
-      // The selected stop is still useful if the optional nearby lookup fails.
-    }
-    const selectedIndex = nearbyData.stops.findIndex(
-      stop => stop.type === data.stop.type && stop.id === data.stop.id
-    );
-    if (selectedIndex === -1) nearbyData.stops.unshift(data.stop);
-    else nearbyData.stops[selectedIndex] = data.stop;
-    renderStops(nearbyData, true);
     returnToResults = true;
     returnViaHistory = false;
     await selectStop(data.stop, false);
@@ -245,6 +227,7 @@ function setSearchMarker(locationResult, label) {
 }
 
 function renderStops(data, fitMap = true, sortOrigin = null, preserveSelection = false) {
+  if (data.kind !== 'map') loadedMapBounds = null;
   const origin = data.location || sortOrigin;
   stops = [...data.stops]
     .map(stop => ({...stop, distance_metres: distanceMetres(stop, origin)}))
@@ -592,6 +575,7 @@ async function loadVisibleMapStops() {
   if (map.getZoom() < MIN_MAP_STOP_ZOOM) {
     markers.clearLayers();
     clearHoveredStop();
+    loadedMapBounds = null;
     byId('map-status').textContent = 'Zoom in to load transport stops';
     show('map-status');
     return;
@@ -609,6 +593,14 @@ async function loadVisibleMapStops() {
       lat: center.lat.toFixed(6), lon: center.lng.toFixed(6),
     }), true);
   }
+  if (loadedMapBounds && loadedMapBounds.contains(bounds)) {
+    if (mapRequestController) {
+      mapRequestController.abort();
+      mapRequestController = null;
+    }
+    show('map-status', false);
+    return;
+  }
   byId('map-status').textContent = 'Loading stops in this area…';
   show('map-status');
   if (mapRequestController) mapRequestController.abort();
@@ -619,6 +611,8 @@ async function loadVisibleMapStops() {
     });
     const data = await response.json();
     if (!response.ok) throw new Error(data.message || 'Could not load this map area.');
+    // A capped result may be incomplete, so do not reuse its coverage when zooming in.
+    loadedMapBounds = data.stops.length < 1000 ? bounds : null;
     renderStops(data, false, map.getCenter(), Boolean(selectedStop));
     show('map-status', false);
   } catch (error) {
diff --git a/tests/test_uk_bus_stops_playwright.py b/tests/test_uk_bus_stops_playwright.py
index 11a1d35..a6e7091 100644
--- a/tests/test_uk_bus_stops_playwright.py
+++ b/tests/test_uk_bus_stops_playwright.py
@@ -122,7 +122,7 @@ def test_search_and_stop_details_in_browser(chromium_browser: Any, flask_url: st
 
 
 def test_moving_map_loads_only_when_zoomed_in(chromium_browser: Any, flask_url: str) -> None:
-    """Panning a close map loads visible stops while a wide map makes no query."""
+    """Map loads skip wide views and zoom-ins already covered by fetched bounds."""
     page = chromium_browser.new_page(viewport={"width": 1280, "height": 800})
     requests: list[str] = []
 
@@ -154,13 +154,13 @@ def test_moving_map_loads_only_when_zoomed_in(chromium_browser: Any, flask_url:
     playwright_api.expect(page.locator("#stop-name")).to_have_text("Temple Meads")
     page.wait_for_timeout(700)
     playwright_api.expect(page.locator("#stop-detail")).to_be_visible()
-    assert len(requests) == 3
-    page.evaluate("userMapInteractionPending = true; map.panBy([80, 0])")
+    assert len(requests) == 2
+    page.evaluate("userMapInteractionPending = true; map.panBy([2500, 0])")
     page.wait_for_timeout(700)
     playwright_api.expect(page.locator("#stop-name")).to_have_text("Temple Meads")
     playwright_api.expect(page.locator("#stop-detail")).to_be_visible()
     playwright_api.expect(page).to_have_url(re.compile(r"\?node=456$"))
-    assert len(requests) == 4
+    assert len(requests) == 3
     page.close()