editor/src/libs/layerwatcher.ts

import throttle from "lodash.throttle";
import isEqual from "lodash.isequal";
import { type Map } from "maplibre-gl";

export type LayerWatcherOptions = {
  onSourcesChange?: (sources: { [sourceId: string]: string[] }) => void;
  onVectorLayersChange?: (vectorLayers: { [vectorLayerId: string]: { [propertyName: string]: { [propertyValue: string]: {} } } }) => void;
};

/** Listens to map events to build up a store of available vector
 * layers contained in the tiles */
export default class LayerWatcher {
  onSourcesChange: (sources: { [sourceId: string]: string[] }) => void;
  onVectorLayersChange: (vectorLayers: { [vectorLayerId: string]: { [propertyName: string]: { [propertyValue: string]: {} } } }) => void;
  throttledAnalyzeVectorLayerFields: (map: any) => void;
  _sources: { [sourceId: string]: string[] };
  _vectorLayers: { [vectorLayerId: string]: { [propertyName: string]: { [propertyValue: string]: {} } } };

  constructor(opts: LayerWatcherOptions = {}) {
    this.onSourcesChange = opts.onSourcesChange || (() => {});
    this.onVectorLayersChange = opts.onVectorLayersChange || (() => {});

    this._sources = {};
    this._vectorLayers = {};

    // Since we scan over all features we want to avoid this as much as
    // possible and only do it after a batch of data has loaded because
    // we only care eventuall about knowing the fields in the vector layers
    this.throttledAnalyzeVectorLayerFields = throttle(this.analyzeVectorLayerFields, 5000);
  }

  analyzeMap(map: Map) {
    const previousSources = { ...this._sources };

    for (const sourceId of Object.keys(map.style.tileManagers)) {
      //NOTE: This heavily depends on the internal API of Maplibre GL
      //so this breaks between Maplibre GL JS releases
      this._sources[sourceId] = map.style.tileManagers[sourceId]._source.vectorLayerIds as string[];
    };

    if(!isEqual(previousSources, this._sources)) {
      this.onSourcesChange(this._sources);
    }

    this.throttledAnalyzeVectorLayerFields(map);
  }

  analyzeVectorLayerFields(map: Map) {
    const previousVectorLayers = { ...this._vectorLayers };

    Object.keys(this._sources).forEach(sourceId => {
      (this._sources[sourceId] || []).forEach(vectorLayerId => {
        const knownProperties = this._vectorLayers[vectorLayerId] || {};
        const params = { sourceLayer: vectorLayerId };
        map.querySourceFeatures(sourceId, params as any).forEach(feature => {
          Object.keys(feature.properties).forEach(propertyName => {
            const knownPropertyValues = knownProperties[propertyName] || {};
            knownPropertyValues[feature.properties[propertyName]] = {};
            knownProperties[propertyName] = knownPropertyValues;
          });
        });

        this._vectorLayers[vectorLayerId] = knownProperties;
      });
    });

    if(!isEqual(previousVectorLayers, this._vectorLayers)) {
      this.onVectorLayersChange(this._vectorLayers);
    }

  }

  /** Access all known sources and their vector tile ids */
  get sources() {
    return this._sources;
  }

  get vectorLayers() {
    return this._vectorLayers;
  }
}