sac-route-portal-gpx-fx/background.js

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

let gpxTrack = null;

/**
 * Convert the Swiss projection coordinates to WGS84 (lat/lon).
 *
 * Calculations from "Approximate formulas for the transformation between Swiss
 * projection coordinates and WGS84" by the Swiss Federal Office of Topography,
 * swisstopo
 * (https://www.swisstopo.admin.ch/en/knowledge-facts/surveying-geodesy/reference-systems/map-projections.html).
 *
 * @param {*} point Array of Swiss projection coordinates, position 0 is E and 1 is N.
 * @returns Calculated lat and lon.
 */
function toWGS84(point) {
  // convert LV95 into the civilian system
  let y_aux = (point[0] - 2600000) / 1000000;
  let x_aux = (point[1] - 1200000) / 1000000;

  // calculate longitude and latitude in the unit 10000"
  let lat = 16.9023892 +
    3.238272 * x_aux -
    0.270978 * Math.pow(y_aux, 2) -
    0.002528 * Math.pow(x_aux, 2) -
    0.0447 * Math.pow(y_aux, 2) * x_aux -
    0.0140 * Math.pow(x_aux, 3);

  let lon = 2.6779094 +
    4.728982 * y_aux +
    0.791484 * y_aux * x_aux +
    0.1306 * y_aux * Math.pow(x_aux, 2) -
    0.0436 * Math.pow(y_aux, 3);

  // unit 10000" to 1" and seconds to degrees (dec)
  lat = lat * 100 / 36;
  lon = lon * 100 / 36;

  return { lat: lat, lon: lon };
}

/**
 * Get the gpx trackpoint representation of a Swiss projection coordinate point.
 *
 * @param {*} point Array of Swiss projection coordinates, position 0 is E and 1 is N.
 * @returns Track point xml node for gpx.
 */
function toTrackPoint(point) {
  let wgs84Point = toWGS84(point);
  return `<trkpt lat="${wgs84Point.lat}" lon="${wgs84Point.lon}"/>`;
}

/**
 * Get the gpx waypoint representation of a route portal point.
 *
 * @returns Way point xml node for gpx.
 */
function toWayPoint(point) {
  let wgs84Point = toWGS84(point.geom.coordinates);
  return `
    <wpt lat="${wgs84Point.lat}" lon="${wgs84Point.lon}">
        <ele>${point.altitude}</ele>
        <name>${point.display_name}</name>
    </wpt>`;
}

/**
 * Create track title.
 *
 * @param {*} geoJson
 * @returns Combined route number, id and route title.
 */
function trackTitle(geoJson) {
  const route = geoJson.segments[0];
  const book = geoJson.book_route_number
    ? `${geoJson.book_route_number} - `
    : "";

  return `${book}${geoJson.title}`;
}

/**
 * Create a gpx representation from the sac GeoJSON data.
 *
 * @param {*} geoJson
 * @returns Simple gpx string.
 */
function toGpx(geoJson) {
  let trackSegments = geoJson.segments.map((segment) => {
    return `<trkseg>
            ${segment.geom.coordinates.map(toTrackPoint).join("")}
        </trkseg>`;
  }).join("");

  let endPoint = geoJson.end_point ? toWayPoint(geoJson.end_point) : "";
  let waypoints = geoJson.waypoints
    ? geoJson.waypoints.map((wp) => {
      return toWayPoint(wp.reference_poi);
    }).join("")
    : "";

  const routeTitle = trackTitle(geoJson);

  const xmlString = `<?xml version="1.0" encoding="UTF-8" standalone="no" ?>

    <gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="http://www.topografix.com/GPX/1/0"
        xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd"
        version="1.0"
        creator="SAC-Tourenportal GPX Downloader">
      ${toWayPoint(geoJson.departure_point)}
      ${toWayPoint(geoJson.destination_poi)}
      ${waypoints}
      ${endPoint}
      <trk>
        <name>Track ${routeTitle}</name>
        ${trackSegments}
      </trk>
    </gpx>
    `;

  const parser = new DOMParser();
  let xmlDoc = parser.parseFromString(xmlString, "text/xml");

  return new XMLSerializer().serializeToString(xmlDoc.documentElement);
}

/**
 * Intercept the download of GeoJSON data and save it for the background script.
 */
function listener(details) {
  let filter = browser.webRequest.filterResponseData(details.requestId);
  let decoder = new TextDecoder("utf-8");
  let encoder = new TextEncoder();

  let data = [];
  filter.ondata = (event) => {
    data.push(event.data);
  };

  filter.onstop = async (event) => {
    let blob = new Blob(data, { type: "text/html" });
    let buffer = await blob.arrayBuffer();
    let str = decoder.decode(buffer);

    updateActiveTab(browser.tabs);

    filter.write(encoder.encode(str));
    filter.close();

    let geoJson = JSON.parse(str);
    const routeTitle = trackTitle(geoJson);
    gpxTrack = { title: routeTitle, data: toGpx(geoJson) };
  };

  return {};
}

/**
 * Check if a url should be intercepted.
 *
 * @param {*} tab
 * @returns True if the active tab is an sac website, false otherwise.
 */
function checkTrack(tab) {
  if (!tab.url) {
    return false;
  }

  return tab.url.match("https://www.sac-cas.ch/.*") && gpxTrack;
}

/**
 * If a valid tack was selected, download it as a gpx file.
 */
function handleClick(tab) {
  const hasTrack = checkTrack(tab);
  if (!hasTrack) {
    return;
  }

  let blob = new Blob([gpxTrack.data], { type: "application/gpx+xml" });
  let objectURL = URL.createObjectURL(blob);

  let downloading = browser.downloads.download({
    url: objectURL,
    filename: `${gpxTrack.title}.gpx`,
    saveAs: true,
    conflictAction: "uniquify",
  });

  downloading.then(
    (id) => console.log(`Started downloading: ${id}`),
    (error) => console.log(`Download failed: ${error}`),
  );
  gpxTrack = null;
}

/**
 * Update the download icon and text.
 */
function updateActiveTab(tabs) {
  function updateTab(tabs) {
    if (tabs[0]) {
      updateIcon(tabs[0]);
    }
  }

  let gettingActiveTab = browser.tabs.query({
    active: true,
    currentWindow: true,
  });
  gettingActiveTab.then(updateTab);
}

/**
 * Update the download icon.
 */
function updateIcon(tab) {
  const hasTrack = checkTrack(tab);

  browser.browserAction.setIcon({
    path: hasTrack
      ? {
        48: "icons/map.png",
      }
      : {
        48: "icons/map-disabled.png",
      },
    tabId: tab.id,
  });
  browser.browserAction.setTitle({
    title: hasTrack
      ? `Download track "${gpxTrack.title}"`
      : "No track selected",
    tabId: tab.id,
  });
}

browser.webRequest.onBeforeRequest.addListener(
  listener,
  { urls: ["https://www.sac-cas.ch/*[routeId]*"] },
  ["blocking"],
);

browser.browserAction.onClicked.addListener(handleClick);

browser.tabs.onUpdated.addListener(updateActiveTab);
browser.tabs.onActivated.addListener(updateActiveTab);
browser.windows.onFocusChanged.addListener(updateActiveTab);

updateActiveTab();