map position in url

Signed-off-by: K1 <git@karoh.net>

dve.js

@@ -9,6 +9,7 @@ const zoom = 14;
 const mapCounts = [2, 4, 6, 9];
 
 let syncing = false;
+let urlUpdateTimer = null;
 
 let TILE_SERVERS = [];
 let maps = [];
@@ -23,6 +24,39 @@ function fillDropdown(select) {
   }
 }
 
+function readUrlPosition() {
+  const match = window.location.hash.match(/^#map=([0-9.]+)\/(-?[0-9.]+)\/(-?[0-9.]+)/);
+
+  if (match) {
+    const z = parseFloat(match[1]);
+    const lat = parseFloat(match[2]);
+    const lng = parseFloat(match[3]);
+
+    if (Number.isFinite(lat) && Number.isFinite(lng) && Number.isFinite(z)) {
+      return {
+        center: [lat, lng],
+        zoom: z
+      };
+    }
+  }
+
+  return {
+    center,
+    zoom
+  };
+}
+
+function writeUrlPosition(map) {
+  if (urlUpdateTimer) clearTimeout(urlUpdateTimer);
+
+  urlUpdateTimer = setTimeout(() => {
+    const c = map.getCenter();
+    const hash = "#map=" + map.getZoom() + "/" + c.lat.toFixed(5) + "/" + c.lng.toFixed(5);
+
+    history.replaceState(null, "", hash);
+  }, 100);
+}
+
 function sync(source) {
   if (syncing) return;
   syncing = true;
@@ -32,6 +66,8 @@ function sync(source) {
     }
   });
   syncing = false;
+
+  writeUrlPosition(source);
 }
 
 function setLayer(map, config, currentLayer) {
@@ -85,6 +121,7 @@ function setMapCount(count) {
 }
 
 function init() {
+  const urlPosition = readUrlPosition();
   const mapCountSelector = document.getElementById("mapCountSelector");
   fillMapCountDropdown(mapCountSelector);
 
@@ -92,7 +129,7 @@ function init() {
     const select = document.getElementById("select" + i);
     fillDropdown(select);
 
-    const map = L.map("map" + i, { center, zoom, zoomControl: false });
+    const map = L.map("map" + i, { center: urlPosition.center, zoom: urlPosition.zoom, zoomControl: false });
     map.on("move", () => sync(map));
     map.on("zoom", () => sync(map));