maptool/public/js/locate.js

import { Marker } from "/vendor/maplibre-gl/maplibre-gl.mjs";

// Replaces MapLibre's own GeolocateControl (browser Geolocation API only)
// with one that prefers this app's own GNSS receiver when it's turned on
// (the sidebar "GNSS" icon, GnssControl) over a phone/laptop's separate
// (and often less accurate, e.g. wifi-based) location service. GNSS itself
// is only ever used here when explicitly enabled via that sidebar
// control — not just whenever a receiver happens to have a fix — so this
// doesn't do any polling of its own for that case; GnssControl already
// does, and already keeps the map following it once enabled, the same way
// this control's own browser-geolocation fallback follows below.
//
// Reuses MapLibre's own geolocate button styling (same classes/icon
// GeolocateControl itself uses, maplibre-gl.css) rather than a new icon —
// visually a drop-in replacement, just sourced differently.
export class LocateControl {
  constructor(gnssControl) {
    this._gnssControl = gnssControl;
    this._active = false;
    this._marker = null;
    this._watchId = null;
  }

  onAdd(map) {
    this._map = map;
    this._button = document.createElement("button");
    this._button.type = "button";
    this._button.className = "maplibregl-ctrl-geolocate";
    this._button.title = "Find my location";
    this._button.setAttribute("aria-label", "Find my location");
    const icon = document.createElement("span");
    icon.className = "maplibregl-ctrl-icon";
    icon.setAttribute("aria-hidden", "true");
    this._button.appendChild(icon);
    this._button.addEventListener("click", () => this._click());

    this._container = document.createElement("div");
    this._container.className = "maplibregl-ctrl maplibregl-ctrl-group";
    this._container.appendChild(this._button);
    return this._container;
  }

  onRemove() {
    this._stop();
    this._container.remove();
  }

  getDefaultPosition() {
    return "top-left";
  }

  _click() {
    if (this._gnssControl.isEnabled()) {
      // GNSS already follows the map on its own once enabled (GnssControl)
      // and has no separate "off" state to toggle from here — just jump to
      // its current fix now, for the same instant feedback clicking this
      // button has always given.
      const position = this._gnssControl.getPosition();
      if (position) {
        this._map.flyTo({ center: position, zoom: Math.max(this._map.getZoom(), 15) });
      } else {
        window.alert("Waiting for a GNSS fix…");
      }
      return;
    }

    if (this._active) {
      this._stop();
    } else {
      this._start();
    }
  }

  _start() {
    this._active = true;
    this._button.classList.add("maplibregl-ctrl-geolocate-active");
    this._watchId = navigator.geolocation.watchPosition(
      (position) => this._setPosition(position.coords.longitude, position.coords.latitude),
      () => {
        window.alert("Could not determine your location.");
        this._stop();
      },
      { enableHighAccuracy: true },
    );
  }

  // Recenters on every fix, following the position the way GeolocateControl
  // itself does while tracking — flyTo (with its zoom swoop) only for the
  // first fix, since that's the one jumping from wherever the map already
  // was; easeTo for later updates, a plain pan/zoom-preserving follow
  // rather than repeating that same swoop on every update.
  _setPosition(lon, lat) {
    if (!this._marker) {
      const el = document.createElement("div");
      el.className = "gnss-marker";
      this._marker = new Marker({ element: el }).setLngLat([lon, lat]).addTo(this._map);
      this._map.flyTo({ center: [lon, lat], zoom: Math.max(this._map.getZoom(), 15) });
    } else {
      this._marker.setLngLat([lon, lat]);
      this._map.easeTo({ center: [lon, lat] });
    }
  }

  _stop() {
    this._active = false;
    this._button.classList.remove("maplibregl-ctrl-geolocate-active");
    if (this._watchId !== null) {
      navigator.geolocation.clearWatch(this._watchId);
      this._watchId = null;
    }
    if (this._marker) {
      this._marker.remove();
      this._marker = null;
    }
  }
}