Fetch and render trip elements on the map (#3)

Adds an Elements GraphQL query bound to the visible map viewport and
renders each element with a location as an emoji-icon pin. The query
is gated on the initial fly-to so we don't fetch the whole world at
the default zoom-1 framing, and re-runs as the user pans/zooms via
onRegionDidChange.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dfalling

src/graphql/__generated__/types.ts

@@ -0,0 +1,12 @@
+query Elements($bounds: GeoBounds) {
+  elements(bounds: $bounds) {
+    id
+    name
+    icon
+    location {
+      id
+      latitude
+      longitude
+    }
+  }
+}

src/graphql/queries/elements.graphql

@@ -3,11 +3,18 @@ import {
   type CameraRef,
   LocationManager,
   Map as MapLibreMap,
+  Marker,
   UserLocation,
   useCurrentPosition,
+  type ViewStateChangeEvent,
 } from '@maplibre/maplibre-react-native';
-import {useEffect, useRef, useState} from 'react';
-import {StyleSheet, View} from 'react-native';
+import {useCallback, useEffect, useRef, useState} from 'react';
+import type {NativeSyntheticEvent} from 'react-native';
+import {StyleSheet, Text, View} from 'react-native';
+import {
+  type ElementsQueryVariables,
+  useElementsQuery,
+} from '../graphql/__generated__/types';
 
 const MAP_STYLE = 'https://tiles.openfreemap.org/styles/liberty';
 const USER_ZOOM = 14;
@@ -42,11 +49,44 @@ export function MapScreen() {
     });
   }, [position]);
 
+  const [bounds, setBounds] = useState<ElementsQueryVariables['bounds']>();
+
+  const onRegionDidChange = useCallback(
+    (event: NativeSyntheticEvent<ViewStateChangeEvent>) => {
+      // Skip viewport events until we've flown to the user's location, so
+      // we don't fetch the entire world at the initial zoom-1 framing.
+      if (!hasCenteredRef.current) return;
+      const [west, south, east, north] = event.nativeEvent.bounds;
+      setBounds({left: west, bottom: south, right: east, top: north});
+    },
+    [],
+  );
+
+  const {data} = useElementsQuery({
+    skip: !bounds,
+    variables: bounds ? {bounds} : undefined,
+  });
+
   return (
     <View style={styles.container}>
-      <MapLibreMap mapStyle={MAP_STYLE} style={styles.map}>
+      <MapLibreMap
+        mapStyle={MAP_STYLE}
+        style={styles.map}
+        onRegionDidChange={onRegionDidChange}>
         <Camera ref={cameraRef} initialViewState={{center: [0, 20], zoom: 1}} />
         <UserLocation animated accuracy />
+        {data?.elements.map(el =>
+          el.location ? (
+            <Marker
+              key={el.id}
+              id={el.id}
+              lngLat={[el.location.longitude, el.location.latitude]}>
+              <View style={styles.pin}>
+                {el.icon ? <Text style={styles.pinIcon}>{el.icon}</Text> : null}
+              </View>
+            </Marker>
+          ) : null,
+        )}
       </MapLibreMap>
     </View>
   );
@@ -59,4 +99,19 @@ const styles = StyleSheet.create({
   map: {
     flex: 1,
   },
+  pin: {
+    width: 36,
+    height: 36,
+    borderRadius: 18,
+    backgroundColor: '#1d6fe0',
+    borderWidth: 2,
+    borderColor: '#ffffff',
+    alignItems: 'center',
+    justifyContent: 'center',
+  },
+  pinIcon: {
+    fontSize: 18,
+    lineHeight: 22,
+    textAlign: 'center',
+  },
 });