Meteor Cordova loader with cold start

meteor_cordova_loader.js

/* This file is only loaded on Cordova-bundled apps and is used only in case
 * autoupdate package is used.
 * It checks if File plugin is installed and a newer version of the app code can
 * be found on persistent storage. In that case those files are dynamically
 * added to the page.
 * Otherwise a normal app code is loaded (shipped with the app initially).
 */

// Store the potential used URL on cold-start
var invokeURL;

/**
 * Execute handleOpenURL on Android which isn't triggered
 * automatically contrary to iOS
 */
function androidBridge() {
    cordova.exec(
        handleOpenURL,
        null,
        "LaunchMyApp",
        "checkIntent", []);
}

/**
 * Executed once the URL is caught, set the route to open
 * in invokeURL
 * @param  {string} url full URL opened with the scheme
 */
function handleOpenURL(url) {
    setTimeout(function() {
        // Remove the scheme
        invokeURL = url.replace("aixapp://", "");
        window.location = "http://meteor.local/" + invokeURL;
    }, 0);
}

document.addEventListener("deviceready", function() {
    // On android, execute the Cordova bridge when the device is ready
    // A little delay is required
    // Note : it's done natively on iOS
    setTimeout(function() {
        androidBridge();
    }, 250);
}, false);


(function() {
    var DEBUG_TAG = 'METEOR CORDOVA DEBUG (meteor_cordova_loader.js) ';
    var log = function(msg) {
        console.log(DEBUG_TAG + msg);
    };
    var uriToPath = function(uri) {
        return decodeURI(uri).replace(/^file:\/\//g, '');
    };
    var readFile = function(url, cb) {
        window.resolveLocalFileSystemURL(url, function(fileEntry) {
                var success = function(file) {
                    var reader = new FileReader();
                    reader.onloadend = function(evt) {
                        var result = evt.target.result;
                        cb(null, result);
                    };
                    reader.onerror = fail;
                    reader.readAsText(file);
                };
                var fail = function(evt) {
                    cb(new Error("Failed to load entry: " + url), null);
                };
                fileEntry.file(success, fail);
            },
            // error callback
            function(err) {
                cb(new Error("Failed to resolve entry: " + url), null);
            });
    };

    var loadTries = 0;
    var loadFromLocation = function(location) {
        var cordovaRoot =
            uriToPath(window.location.href).replace(/\/index.html$/, '/');

        var httpd = cordova && cordova.plugins && cordova.plugins.CordovaUpdate;

        var retry = function() {
            loadTries++;
            if (loadTries > 10) {
                // XXX: If this means the app fails, we should probably do exponential backoff
                // or at least show a message
                log('Failed to start the server (too many retries)');
            } else {
                log('Starting the server (retry #' + loadTries + ')');
                loadFromLocation(location);
            }
        };

        setTimeout(function() {
            httpd.startServer({
                'www_root': location,
                'cordovajs_root': cordovaRoot
            }, function(url) {
                // go to the new proxy url
                if (typeof invokeURL !== 'undefined') {
                    // The app has been opened from a scheme, start
                    // the server with the correct route
                    window.location = "http://meteor.local/" + invokeURL;
                } else {
                    // The app was opened without a scheme, start
                    // the server with the default route
                    log("Loading from url: " + url);
                    window.location = url;
                }
            }, function(error) {
                // failed to start a server, is port already in use?
                log("Failed to start the server: " + error);
                retry();
            });
        }, 0);
    };

    // Fallback to the bundled assets from the disk. If an error is passed as an
    // argument, then there was a problem reading from the manifest files. If
    // no error is passed, then we simply do not have any new versions.
    var fallback = function(err) {
        if (err) {
            log("Couldn't load from the manifest, falling back to the bundled assets.");
        } else {
            log('No new versions saved to disk.');
        }
        var location = cordova.file.applicationDirectory + 'www/application/';
        location = uriToPath(location);

        loadFromLocation(location);
    };

    var loadVersion = function(version, localPathPrefix) {
        var versionPrefix = localPathPrefix + version + '/';
        var location = uriToPath(versionPrefix);
        loadFromLocation(location);
    };

    var loadApp = function(localPathPrefix) {
        readFile(localPathPrefix + 'version', function(err, version) {
            if (err) {
                log("Error reading version file " + err);
                fallback(err);
                return;
            }

            loadVersion(version, localPathPrefix);
        });
    };

    document.addEventListener("deviceready", function() {
        var startLoading = function() {
            if (!cordova.file) {
                // If the plugin didn't actually load, try again later.
                // See a larger comment with details in
                // packages/meteor/startup_client.js
                setTimeout(startLoading, 20);
                return;
            }

            var localPathPrefix = cordova.file.dataDirectory + 'meteor/';
            loadApp(localPathPrefix);
        };

        startLoading();
    }, false);
})();

@Exilz can you explain how this script works?