demarches-normaliennes/app/javascript/components/MapEditor/readGeoFile.ts

import { gpx, kml } from '@tmcw/togeojson/dist/togeojson.es.js';
import type { FeatureCollection, Feature } from 'geojson';

import { generateId } from '../shared/maplibre/utils';

export function readGeoFile(file: File) {
  const isGpxFile = file.name.includes('.gpx');
  const reader = new FileReader();

  return new Promise<ReturnType<typeof normalizeFeatureCollection>>(
    (resolve) => {
      reader.onload = (event: FileReaderEventMap['load']) => {
        const result = event.target?.result;
        const xml = new DOMParser().parseFromString(
          result as string,
          'text/xml'
        );
        const featureCollection = normalizeFeatureCollection(
          isGpxFile ? gpx(xml) : kml(xml),
          file.name
        );

        resolve(featureCollection);
      };
      reader.readAsText(file, 'UTF-8');
    }
  );
}

function normalizeFeatureCollection(
  featureCollection: FeatureCollection,
  filename: string
) {
  const features: Feature[] = [];
  for (const feature of featureCollection.features) {
    switch (feature.geometry.type) {
      case 'MultiPoint':
        for (const coordinates of feature.geometry.coordinates) {
          features.push({
            type: 'Feature',
            geometry: {
              type: 'Point',
              coordinates
            },
            properties: feature.properties
          });
        }
        break;
      case 'MultiLineString':
        for (const coordinates of feature.geometry.coordinates) {
          features.push({
            type: 'Feature',
            geometry: {
              type: 'LineString',
              coordinates
            },
            properties: feature.properties
          });
        }
        break;
      case 'MultiPolygon':
        for (const coordinates of feature.geometry.coordinates) {
          features.push({
            type: 'Feature',
            geometry: {
              type: 'Polygon',
              coordinates
            },
            properties: feature.properties
          });
        }
        break;
      case 'GeometryCollection':
        for (const geometry of feature.geometry.geometries) {
          features.push({
            type: 'Feature',
            geometry,
            properties: feature.properties
          });
        }
        break;
      default:
        features.push(feature);
    }
  }

  const featureCollectionFilename = `${generateId()}-${filename}`;
  featureCollection.features = features.map((feature) => ({
    ...feature,
    properties: {
      ...feature.properties,
      filename: featureCollectionFilename
    }
  }));
  return { ...featureCollection, filename: featureCollectionFilename };
}