dve/dve.js

const json_files = [
  "tileconfig/osm.json",
  "tileconfig/mapycom.json",
  "tileconfig/praha.json"
];

const center = [50.08804, 14.42076];
const zoom = 14;
const mapCounts = [2, 4, 6, 9];

let syncing = false;
let urlUpdateTimer = null;

let TILE_SERVERS = [];
let maps = [];
let layers = [];

function fillDropdown(select) {
  for (const name in TILE_SERVERS) {
    const opt = document.createElement("option");
    opt.value = name;
    opt.textContent = name;
    select.appendChild(opt);
  }
}

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;
  maps.forEach(target => {
    if (target !== source) {
      target.setView(source.getCenter(), source.getZoom(), { animate: false });
    }
  });
  syncing = false;

  writeUrlPosition(source);
}

function setLayer(map, config, currentLayer) {
  if (currentLayer) map.removeLayer(currentLayer);

  if (config.type === "xyz") {
    return L.tileLayer(config.url, {
      maxZoom: 19,
      tileSize: 256,
      referrerPolicy: "strict-origin-when-cross-origin"
    }).addTo(map);
  }

  if (config.type === "wms") {
    return L.tileLayer.wms(config.url, {
      layers: config.layers,
      format: config.format || "image/png",
      transparent: config.transparent ?? true,
      version: config.version || "1.3.0",
      attribution: config.attribution || "",
      referrerPolicy: "strict-origin-when-cross-origin"
    }).addTo(map);
  }
}

function fillMapCountDropdown(select) {
  select.innerHTML = "";

  mapCounts.forEach(count => {
    const opt = document.createElement("option");
    opt.value = count;
    opt.textContent = count + (count === 2 || count === 4 ? " mapy" : " map");
    select.appendChild(opt);
  });
}

function setMapCount(count) {
  const container = document.getElementById("container");
  container.dataset.count = count;

  for (let i = 1; i <= maps.length; i++) {
    const wrapper = document.getElementById("map" + i).parentElement;
    wrapper.classList.toggle("hidden", i > count);
  }

  setTimeout(() => {
    maps.forEach((map, index) => {
      if (index < count) map.invalidateSize(false);
    });
  }, 0);
}

function init() {
  const urlPosition = readUrlPosition();
  const mapCountSelector = document.getElementById("mapCountSelector");
  fillMapCountDropdown(mapCountSelector);

  for (let i = 1; i <= 9; i++) {
    const select = document.getElementById("select" + i);
    fillDropdown(select);

    const map = L.map("map" + i, { center: urlPosition.center, zoom: urlPosition.zoom, zoomControl: false });
    map.on("move", () => sync(map));
    map.on("zoom", () => sync(map));

    L.control.zoom({ position: "topright" }).addTo(map);

    maps.push(map);
    layers.push(null);

    layers[i - 1] = setLayer(map, TILE_SERVERS[select.value], layers[i - 1]);

    select.addEventListener("change", e => {
      const key = e.target.value;
      layers[i - 1] = setLayer(map, TILE_SERVERS[key], layers[i - 1]);
    });
  }

  mapCountSelector.value = "2";
  mapCountSelector.addEventListener("change", e => {
    setMapCount(parseInt(e.target.value, 10));
  });

  setMapCount(parseInt(mapCountSelector.value, 10));
}

async function loadTileConfigs(json_files) {
  const results = await Promise.all(
    json_files.map(f => fetch(f).then(r => r.json()))
  );

  // Merge all JSON objects into TILE_SERVERS
  results.forEach(obj => Object.assign(TILE_SERVERS, obj));
}

loadTileConfigs(json_files).then(() => {
  init();
});