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 Track point xml node for gpx.
 */
function toTrackPoint(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 lng = 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;
	lng = lng * 100 / 36;

    return `<trkpt lat="${lat}" lon="${lng}"/>`;
}

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

/**
 * Create a gpx representation from the sac GeoJSON data.
 * 
 * @param {*} geoJson 
 * @returns Simple gpx string.
 */
function toGpx(geoJson) {
    const route = geoJson.segments[0].geom;
    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">
      <trk>
        <name>Track ${routeTitle}</name>
        <trkseg>
            ${route.coordinates.map(toTrackPoint).join("")}
        </trkseg>
      </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);

        gpxTrack = JSON.parse(str);
        updateActiveTab(browser.tabs);

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

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

    const routeTitle = trackTitle(gpxTrack);

    let downloading = browser.downloads.download({
        url : objectURL,
        filename : `track-${routeTitle}.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 ${trackTitle(gpxTrack)}` : '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();