feat: encode map position and zoom in URL

mapper/src/App.js

@@ -1,6 +1,6 @@
 import React, { useState, useEffect } from 'react';
 import * as leaflet from 'leaflet';
-import { MapContainer, Polyline, TileLayer, useMap } from 'react-leaflet';
+import { MapContainer, Polyline, TileLayer, useMap, useMapEvents } from 'react-leaflet';
 import Datetime from 'react-datetime';
 import 'react-datetime/css/react-datetime.css';
 import axios from 'axios';
@@ -71,14 +71,39 @@ function useSensor(measurement, name, end, duration) {
 };
 
 
+function ChangeView({ center, zoom }) {
+    const map = useMap();
+    map.setView(center, zoom);
+    return null;
+}
 
-function Map({end, duration, slider}) {
+function MapEvents({ onMapChange }) {
+    const map = useMapEvents({
+        moveend: () => {
+            const center = map.getCenter();
+            onMapChange({
+                zoom: map.getZoom(),
+                center: [center.lat, center.lng],
+            });
+        },
+    });
+    return null;
+}
+
+function Map({end, duration, slider, mapState, setMapState}) {
 	const [data, loading] = useSensor('owntracks', 'OwnTracks', end, duration);
 
 	const range = parseSlider(end, duration, slider);
 
 	const coords = data.length ? data.filter(x => !range || (x.time >= range[0] && x.time <= range[1])).map(({ lat, lon }) => [lat, lon]).filter(([lat, lon]) => lat !== null || lon !== null) : [];
 
+	useEffect(() => {
+		// If URL provides no center, set it from the data once it's loaded.
+		if (mapState.center === null && coords.length > 0) {
+			setMapState(prev => ({ ...prev, center: coords[coords.length - 1] }));
+		}
+	}, [coords, mapState.center, setMapState]);
+
 	const handleSubmit = (e) => {
 		e.preventDefault();
 		const api_key = e.target[0].value;
@@ -91,13 +116,17 @@ function Map({end, duration, slider}) {
 				<p>Loading...</p>
 			:
 				coords.length ?
-					<MapContainer center={coords[coords.length-1]} zoom={13} scrollWheelZoom={true} style={{ width: '100%', height: 'calc(100vh - 2.5rem)' }}>
+					(mapState.center &&
+						<MapContainer center={mapState.center} zoom={mapState.zoom} scrollWheelZoom={true} style={{ width: '100%', height: 'calc(100vh - 2.5rem)' }}>
+							<ChangeView center={mapState.center} zoom={mapState.zoom} />
+							<MapEvents onMapChange={setMapState} />
 							<TileLayer
 								attribution='&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
 								url='https://maptiles.p.rapidapi.com/en/map/v1/{z}/{x}/{y}.png?rapidapi-key=4375b0b1d8msh0c9e7fa3efb9adfp1769dfjsnd603a0387fea'
 							/>
 							<Polyline pathOptions={{color: 'blue'}} positions={coords} />
 						</MapContainer>
+					)
 				:
 					<>
 						<p>No data</p>
@@ -284,6 +313,9 @@ function App() {
 	const initialDurationId = params.get('duration');
 	const initialEndTimestamp = params.get('end');
 	const initialSliderValue = params.get('slider');
+	const initialLat = params.get('lat');
+	const initialLng = params.get('lng');
+	const initialZoom = params.get('zoom');
 
 	const initialDuration = (initialDurationId && durations[parseInt(initialDurationId, 10)]) ? durations[parseInt(initialDurationId, 10)] : durations[0];
 	const initialEnd = initialEndTimestamp ? moment.unix(initialEndTimestamp) : moment();
@@ -292,6 +324,10 @@ function App() {
 	const [duration, setDuration] = useState(initialDuration);
 	const [end, setEnd] = useState(initialEnd);
 	const [slider, setSlider] = useState(initialSlider);
+	const [mapState, setMapState] = useState({
+		center: (initialLat && initialLng) ? [parseFloat(initialLat), parseFloat(initialLng)] : null,
+		zoom: initialZoom ? parseInt(initialZoom, 10) : 13,
+	});
 
 	useEffect(() => {
 		const handler = setTimeout(() => {
@@ -299,13 +335,18 @@ function App() {
 			params.set('duration', duration.id);
 			params.set('end', end.unix());
 			params.set('slider', slider.join(','));
+			if (mapState.center) {
+				params.set('lat', mapState.center[0].toFixed(5));
+				params.set('lng', mapState.center[1].toFixed(5));
+				params.set('zoom', mapState.zoom);
+			}
 			window.history.replaceState({}, '', `${window.location.pathname}?${params.toString()}`);
 		}, 500);
 
 		return () => {
 			clearTimeout(handler);
 		};
-	}, [duration, end, slider]);
+	}, [duration, end, slider, mapState]);
 
 	return (
 		<div>
@@ -322,6 +363,8 @@ function App() {
 				end={end}
 				duration={duration}
 				slider={slider}
+				mapState={mapState}
+				setMapState={setMapState}
 			/>
 		</div>
 	);