/**
 * service-worker.js : Service Worker implementation,
 * in order to capture the HTTP requests made by an article, and respond with the
 * corresponding content, coming from the archive
 * 
 * Copyright 2022 Mossroy, Jaifroid and contributors
 * License GPL v3:
 * 
 * This file is part of Kiwix.
 * 
 * Kiwix is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * Kiwix is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with Kiwix (file LICENSE-GPLv3.txt).  If not, see <http://www.gnu.org/licenses/>
 */
'use strict';

/**
 * App version number - ENSURE IT MATCHES VALUE IN init.js
 * DEV: Changing this will cause the browser to recognize that the Service Worker has changed, and it will
 * download and install a new copy; we have to hard code this here because it is needed before any other file
 * is cached in APP_CACHE
 */
const appVersion = '2.2.0';

/**
 * The name of the Cache API cache in which assets defined in regexpCachedContentTypes will be stored
 * The value is sometimes needed here before it can be passed from app.js, so we have to duplicate it
 * @type {String}
 */
// DEV: Ensure this matches the name defined in cache.js. Note this is interoperable with Kiwix JS.
const ASSETS_CACHE = 'kiwixjs-assetsCache';

/**
 * The name of the application cache to use for caching online code so that it can be used offline
 * The cache name is made up of the prefix below and the appVersion: this is necessary so that when
 * the app is updated, a new cache is created. The new cache will start being used after the user
 * restarts the app, when we will also delete the old cache.
 * @type {String}
 */
const APP_CACHE = 'kiwix-appCache-' + appVersion;

/**
 * A global Boolean that governs whether ASSETS_CACHE will be used
 * Caching is on by default but can be turned off by the user in Configuration
 * @type {Boolean}
 */
var useAssetsCache = true;

/**
 * A global Boolean that governs whether the APP_CACHE will be used
 * This is an expert setting in Configuration
 * @type {Boolean}
 */
 var useAppCache = true;

/**
 * A Boolean that governs whether images are displayed
 * app.js can alter this variable via messaging
 */
let imageDisplay;

// Kiwix ZIM Archive Download Server in regex form
// DEV: The server URL is defined in init.js, but is not available to us in SW
const regexpKiwixDownloadLinks = /download\.kiwix\.org/i;


/**  
 * A regular expression that matches the Content-Types of assets that may be stored in ASSETS_CACHE
 * Add any further Content-Types you wish to cache to the regexp, separated by '|'
 * @type {RegExp}
 */
const regexpCachedContentTypes = /text\/css|\/javascript|application\/javascript/i;

/**
 * A regular expression that excludes listed schemata from caching attempts
 * As of 08-2019 the chrome-extension: schema is incompatible with the Cache API
 * 'example-extension' is included to show how to add another schema if necessary
 * @type {RegExp}
 */
const regexpExcludedURLSchema = /^(?:file|chrome-extension|example-extension):/i;

/** 
 * Pattern for ZIM file namespace: see https://wiki.openzim.org/wiki/ZIM_file_format#Namespaces
 * In our case, there is also the ZIM file name used as a prefix in the URL
 * @type {RegExp}
 */
const regexpZIMUrlWithNamespace = /(?:^|\/)([^/]+\/)([-ABCHIJMUVWX])\/(.+)/;

/**
 * Pattern to parse the first offset of a "range" request header
 * NB: this only reads the first offset of the first byte range, where the spec allows several ranges, and several units.
 * See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Range
 * But, in our case, we send a header to tell the browser we only accept the bytes unit.
 * I did not see multiple ranges asked by a browser.
 * 
 * @type {RegExp}
 */
const regexpByteRangeHeader = /^\s*bytes=(\d+)-/;

/**
 * The list of files that the app needs in order to run entirely from offline code
 */
let precacheFiles = [
    ".", // This caches the redirect to www/index.html, in case a user launches the app from its root directory
  "manifest.json",
  "service-worker.js",
  "www/favicon.ico",
  "www/-/mw/ext.cite.styles.css",
  "www/-/mw/ext.cite.ux-enhancements.css",
  "www/-/mw/ext.math.scripts.css",
  "www/-/mw/ext.math.styles.css",
  "www/-/mw/ext.kartographer.frame.css",
  "www/-/mw/ext.kartographer.link.css",
  "www/-/mw/ext.kartographer.style.css",
  "www/-/mw/ext.scribunto.logs.css",
  "www/-/mw/ext.tmh.thumbnail.styles.css",
  "www/-/mw/inserted_style.css",
  "www/-/mw/inserted_style_mobile.css",
  "www/-/mw/mediawiki.page.gallery.styles.css",
  "www/-/mw/mobile.css",
  "www/-/mw/mw.MediaWikiPlayer.loader.css",
  "www/-/mw/mw.PopUpMediaTransform.css",
  "www/-/mw/mw.TMHGalleryHook.js.css",
  "www/-/mw/style.css",
  "www/-/s/css_modules/content.parsoid.css",
  "www/-/s/css_modules/ext.cite.a11y.css",
  "www/-/s/css_modules/ext.cite.styles.css",
  "www/-/s/css_modules/ext.cite.ux-enhancements.css",
  "www/-/s/css_modules/ext.inputBox.styles.css",
  "www/-/s/css_modules/ext.kartographer.frame.css",
  "www/-/s/css_modules/ext.kartographer.link.css",
  "www/-/s/css_modules/ext.kartographer.style.css",
  "www/-/s/css_modules/inserted_style.css",
  "www/-/s/css_modules/inserted_style_mobile.css",
  "www/-/s/css_modules/mobile.css",
  "www/-/s/css_modules/style.css",
  "www/-/style.css",
  "www/-/s/style.css",
  "www/-/s/style-dark.css",
  "www/-/s/style-dark-invert.css",
  "www/-/s/style-mobile.css",
  "www/-/s/vector.css",
  "www/I/COVID-19_lifecycle.jpg",
  "www/I/s/Icon_External_Link.png",
  "www/I/s/Icons-mini-file_acrobat.gif",
  "www/css/app.css",
  "www/css/bootstrap.min.css",
  "www/fonts/glyphicons-halflings-regular.woff2",
  "www/img/icons/kiwix-256.png",
  "www/img/icons/kiwix-192.png",
  "www/img/icons/kiwix-32.png",
  "www/img/icons/kiwix-60.png",
  "www/img/icons/kiwix-blue-32.png",
  "www/img/icons/kiwix-midnightblue-90.png",
  "www/img/icons/wikimed-blue-32.png",
  "www/img/icons/wikimed-lightblue-32.png",
  "www/img/icons/wikivoyage-90-white.png",
  "www/img/icons/wikivoyage-black-32.png",
  "www/img/icons/wikivoyage-white-32.png",
  "www/img/icons/map_marker-30px.png",
  "www/img/icons/map_marker-18px.png",
  "www/img/spinner.gif",
  "www/index.html",
  "www/article.html",
  "www/js/app.js",
  "www/js/init.js",
  "www/js/lib/arrayFromPolyfill.js",
  "www/js/lib/bootstrap.js",
  "www/js/lib/bootstrap.min.js",
  "www/js/lib/cache.js",
  "www/js/lib/filecache.js",
  "www/js/lib/images.js",
  "www/js/lib/jquery-3.2.1.slim.js",
  "www/js/lib/kiwixServe.js",
  "www/js/lib/promisePolyfill.js",
  "www/js/lib/require.js",
  "www/js/lib/settingsStore.js",
  "www/js/lib/transformStyles.js",
  "www/js/lib/transformZimit.js",
  "www/js/lib/uiUtil.js",
  "www/js/lib/updater.js",
  "www/js/lib/utf8.js",
  "www/js/lib/util.js",
  //"www/js/lib/webpHeroBundle_0.0.0-dev.27.js",
  "www/js/lib/xzdec_wrapper.js",
  "www/js/lib/zstddec_wrapper.js",
  "www/js/lib/zimArchive.js",
  "www/js/lib/zimArchiveLoader.js",
  "www/js/lib/zimDirEntry.js",
  "www/js/lib/zimfile.js",
  "www/js/katex/katex.min.js",
  "www/js/katex/katex.min.css",
  "www/js/katex/contrib/auto-render.min.js",
  "www/js/katex/contrib/copy-tex.min.js",
  "www/js/katex/contrib/mathtex-script-type.min.js",
  "www/js/katex/contrib/mhchem.min.js",
  "www/js/katex/contrib/render-a11y-string.min.js",
  "www/js/katex/fonts/KaTeX_AMS-Regular.woff2",
  "www/js/katex/fonts/KaTeX_Main-Bold.woff2",
  "www/js/katex/fonts/KaTeX_Main-Regular.woff2",
  "www/js/katex/fonts/KaTeX_Math-Italic.woff2",
  "www/js/katex/fonts/KaTeX_Size1-Regular.woff2",
  "www/js/katex/fonts/KaTeX_Size2-Regular.woff2",
  "www/js/katex/fonts/KaTeX_Size3-Regular.woff2",
  "www/js/katex/fonts/KaTeX_Size4-Regular.woff2"
];

if ('WebAssembly' in self) {
  precacheFiles.push(
    "www/js/lib/xzdec-wasm.js",
    "www/js/lib/xzdec-wasm.wasm",
    "www/js/lib/zstddec-wasm.js",
    "www/js/lib/zstddec-wasm.wasm"
  );
} else {
  precacheFiles.push(
    "www/js/lib/xzdec-asm.js",
    "www/js/lib/zstddec-asm.js"
  );
}


// Process install event
self.addEventListener("install", function (event) {
    console.debug("[SW] Install Event processing");
    // DEV: We can't skip waiting because too many params are loaded at an early stage from the old file before the new one can activate...
    // self.skipWaiting();
    // We try to circumvent the browser's cache by adding a header to the Request, and it ensures all files are explicitly versioned
    var requests = precacheFiles.map(function (urlPath) {
        return new Request(urlPath + '?v' + appVersion, { cache: 'no-cache' });
    });
    if (!regexpExcludedURLSchema.test(requests[0].url)) event.waitUntil(
        caches.open(APP_CACHE).then(function (cache) {
            return Promise.all(
                requests.map(function (request) {
                    return fetch(request).then(function (response) {
                        // Fail on 404, 500 etc
                        if (!response.ok) throw Error('Could not fetch ' + request.url);
                        return cache.put(request.url.replace(/\?v[^?/]+$/, ''), response);
                    }).catch(function (err) {
                        console.error('There was an error pre-caching files', err);
                    });
                })
            );
        })
    );
});

// Allow sw to control current page
self.addEventListener('activate', function (event) {
    // "Claiming" the ServiceWorker is necessary to make it work right away,
    // without the need to reload the page.
    // See https://developer.mozilla.org/en-US/docs/Web/API/Clients/claim
    event.waitUntil(self.clients.claim());
    console.debug('[SW] Claiming clients for current page');
    // Check all the cache keys, and delete any old caches
    event.waitUntil(
        caches.keys().then(function (keyList) {
            return Promise.all(keyList.map(function (key) {
                console.debug('[SW] Current cache key is ' + key);
                if (key !== APP_CACHE && key !== ASSETS_CACHE) {
                    console.debug('[SW] App updated to version ' + appVersion + ': deleting old cache');
                    return caches.delete(key);
                }
            }));
        })
    );
});

let outgoingMessagePort = null;
let fetchCaptureEnabled = false;

/**
 * Intercept selected Fetch requests from the browser window
 */
self.addEventListener('fetch', function (event) {
    // Only handle GET or POST requests (POST is intended to handle video in Zimit ZIMs)
    if (!/GET|POST/.test(event.request.method)) return;
    var rqUrl = event.request.url;
    var urlObject = new URL(rqUrl);
    // Test the URL with parameters removed
    var strippedUrl = urlObject.pathname;
    // Test if we're in an Electron app
    // DEV: Electron uses the file:// protocol and hacks it to work with SW, but it has CORS issues when using the Fetch API to fetch local files,
    // so we must bypass it here if we're fetching a local file
    if (/^file:/i.test(rqUrl) && !(regexpZIMUrlWithNamespace.test(strippedUrl) && /\.zim\//i.test(strippedUrl) || /\??iskiwixasset/.test(rqUrl))) return;
    // Don't cache download links
    if (regexpKiwixDownloadLinks.test(rqUrl)) return;
    // Select cache depending on request format
    var cache = /\.zim\//i.test(strippedUrl) ? ASSETS_CACHE : APP_CACHE;
    if (cache === ASSETS_CACHE && !fetchCaptureEnabled) return;
    // For APP_CACHE assets, we should ignore any querystring (whereas it should be conserved for ZIM assets,
    // especially .js assets, where it may be significant). Anchor targets are irreleveant in this context.
    // @TODO DEV: This isn't true for Zimit ZIM types! So we will have to send the zimType from app.js
    if (cache === APP_CACHE) rqUrl = strippedUrl;
    event.respondWith(
        // First see if the content is in the cache
        fromCache(cache, rqUrl).then(function (response) {
            // The response was found in the cache so we respond with it 
            return response;
        }, function () {
            // The response was not found in the cache so we look for it in the ZIM
            // and add it to the cache if it is an asset type (css or js)
            // YouTube links from Zimit archives are dealt with specially
            if (/youtubei.*player/.test(strippedUrl) || cache === ASSETS_CACHE && regexpZIMUrlWithNamespace.test(strippedUrl)) {
                let range = event.request.headers.get('range');
                if (imageDisplay !== 'all' && /\/.*\.(jpe?g|png|svg|gif|webp)(?=.*?kiwix-display)/i.test(rqUrl)) {
                    // If the user has disabled the display of images, and the browser wants an image, respond with empty SVG
                    // A URL without "?kiwix-display" query string acts as a passthrough so that the regex will not match and
                    // the image will be fetched by app.js  
                    // DEV: If you need to hide more image types, add them to regex below and also edit equivalent regex in app.js
                    var svgResponse;
                    if (imageDisplay === 'manual')
                        svgResponse = "<svg xmlns='http://www.w3.org/2000/svg' width='1' height='1'><rect width='1' height='1' style='fill:lightblue'/></svg>";
                    else
                        svgResponse = "<svg xmlns='http://www.w3.org/2000/svg'/>";
                    return new Response(svgResponse, {
                        headers: {
                            'Content-Type': 'image/svg+xml'
                        }
                    });
                }
                return fetchUrlFromZIM(urlObject, range).then(function (response) {
                    // DEV: This is now done in app.js
                    // Add css or js assets to ASSETS_CACHE (or update their cache entries) unless the URL schema is not supported
                    // if (regexpCachedContentTypes.test(response.headers.get('Content-Type')) &&
                    //     !regexpExcludedURLSchema.test(event.request.url)) {
                    //     event.waitUntil(updateCache(ASSETS_CACHE, rqUrl, response.clone()));
                    // }
                    return response;
                }).catch(function (msgPortData) {
                    console.error('Invalid message received from app.js for ' + strippedUrl, msgPortData);
                    return msgPortData;
                });
            } else {
                // It's not an asset, or it doesn't match a ZIM URL pattern, so we should fetch it with Fetch API
                return fetch(event.request).then(function (response) {
                    // DEV: CACHE updating is now done in app.js
                    // If request was successful, add or update it in the cache, but be careful not to cache the ZIM archive itself!
                    // if (!regexpExcludedURLSchema.test(event.request.url) && !/\.zim\w{0,2}$/i.test(strippedUrl)) {
                    //     event.waitUntil(updateCache(APP_CACHE, rqUrl, response.clone()));
                    // }
                    return response;
                }).catch(function (error) {
                    console.debug("[SW] Network request failed and no cache.", error);
                });
            }
        })
    );
});

/**
 * Handle custom commands sent from app.js
 */
 self.addEventListener('message', function (event) {
    if (event.data.action) {
        if (event.data.action === 'init') {
            // On 'init' message, we initialize the outgoingMessagePort and enable the fetchEventListener
            outgoingMessagePort = event.ports[0];
            fetchCaptureEnabled = true;
        } else if (event.data.action === 'disable') {
            // On 'disable' message, we delete the outgoingMessagePort and disable the fetchEventListener
            // outgoingMessagePort = null;
            fetchCaptureEnabled = false;
        }
        var oldValue;
        if (event.data.action.assetsCache) {
            // Turns caching on or off (a string value of 'enable' turns it on, any other string turns it off)
            oldValue = useAssetsCache;
            useAssetsCache = event.data.action.assetsCache === 'enable';
            if (useAssetsCache !== oldValue) console.debug('[SW] Use of assetsCache was switched to: ' + useAssetsCache);
        }
        if (event.data.action.appCache) {
            // Enables or disables use of appCache
            oldValue = useAppCache;
            useAppCache = event.data.action.appCache === 'enable';
            if (useAppCache !== oldValue) console.debug('[SW] Use of appCache was switched to: ' + useAppCache);
        }
        if (event.data.action === 'getCacheNames') {
            event.ports[0].postMessage({ 'app': APP_CACHE, 'assets': ASSETS_CACHE });
        }
        if (event.data.action.checkCache) {
            // Checks and returns the caching strategy: checkCache key should contain a sample URL string to test
            testCacheAndCountAssets(event.data.action.checkCache).then(function (cacheArr) {
                event.ports[0].postMessage({ type: cacheArr[0], name: cacheArr[1], description: cacheArr[2], count: cacheArr[3] });
            });
        }
    }
});

/**
 * Handles URLs that need to be extracted from the ZIM archive
 * 
 * @param {URL} urlObject The URL object to be processed for extraction from the ZIM
 * @param {String} range Optional byte range string
 * @returns {Promise<Response>} A Promise for the Response, or rejects with the invalid message port data
 */
function fetchUrlFromZIM(urlObject, range) {
    return new Promise(function (resolve, reject) {
        // Note that titles may contain bare question marks or hashes, so we must use only the pathname without any URL parameters.
        // Be sure that you haven't encoded any querystring along with the URL.
        var barePathname = decodeURIComponent(urlObject.pathname);
        var partsOfZIMUrl = regexpZIMUrlWithNamespace.exec(barePathname);
        var prefix = partsOfZIMUrl ? partsOfZIMUrl[1] : '';
        var nameSpace = partsOfZIMUrl ? partsOfZIMUrl[2]: '';
        var title = partsOfZIMUrl ? partsOfZIMUrl[3] : barePathname;
        var anchorTarget = urlObject.hash.replace(/^#/, '');
        var uriComponent = urlObject.search.replace(/\?kiwix-display/, '');
        var titleWithNameSpace = nameSpace + '/' + title;

        // Let's instantiate a new messageChannel, to allow app.js to give us the content
        var messageChannel = new MessageChannel();
        messageChannel.port1.onmessage = function (msgPortEvent) {
            if (msgPortEvent.data.action === 'giveContent') {
                // Content received from app.js
                var contentLength = msgPortEvent.data.content ? msgPortEvent.data.content.byteLength : null;
                var contentType = msgPortEvent.data.mimetype;
                // Set the imageDisplay variable if it has been sent in the event data
                imageDisplay = typeof msgPortEvent.data.imageDisplay !== 'undefined' ?
                  msgPortEvent.data.imageDisplay : imageDisplay;
                var headers = new Headers();
                if (contentLength) headers.set('Content-Length', contentLength);
                // Prevent CORS issues in PWAs
                if (contentLength) headers.set('Access-Control-Allow-Origin', '*');
                if (contentType) headers.set('Content-Type', contentType);
                
                // Test if the content is a video or audio file. In this case, Chrome & Edge need us to support ranges.
                // See kiwix-js #519 and openzim/zimwriterfs #113 for why we test for invalid types like "mp4" or "webm" (without "video/")
                // The full list of types produced by zimwriterfs is in https://github.com/openzim/zimwriterfs/blob/master/src/tools.cpp
                if (contentLength >= 1 && /^(video|audio)|(^|\/)(mp4|webm|og[gmv]|mpeg)$/i.test(contentType)) {
                    headers.set('Accept-Ranges', 'bytes');
                }
                
                var slicedData = msgPortEvent.data.content;
                if (range) {
                    // The browser asks for a range of bytes (usually for a video or audio stream)
                    // In this case, we partially honor the request: if it asks for offsets x to y,
                    // we send partial contents starting at x offset, till the end of the data (ignoring y offset)
                    // Our backend can currently only read the whole content from the ZIM file.
                    // So it's probably better to send all we have: hopefully it will avoid some subsequent requests of
                    // the browser to get the following chunks (which would trigger some other complete reads in the ZIM file)
                    // This might be improved in the future with the libzim wasm backend, that should be able to handle ranges.
                    let partsOfRangeHeader = regexpByteRangeHeader.exec(range);
                    let begin = partsOfRangeHeader[1];
                    let end = contentLength - 1;
                    slicedData = slicedData.slice(begin);
                    
                    headers.set('Content-Range', 'bytes ' + begin + '-' + end + '/' + contentLength);
                    headers.set('Content-Length', end - begin + 1);
                }
                
                var responseInit = {
                    // HTTP status is usually 200, but has to bee 206 when partial content (range) is sent
                    status: range ? 206 : 200,
                    statusText: 'OK',
                    headers: headers
                };
                
                var httpResponse = new Response(slicedData, responseInit);

                // Let's send the content back from the ServiceWorker
                resolve(httpResponse);
            } else if (msgPortEvent.data.action === 'sendRedirect') {
                resolve(Response.redirect(prefix + msgPortEvent.data.redirectUrl));
            } else {
                reject(msgPortEvent.data, titleWithNameSpace);
            }
        };
        outgoingMessagePort.postMessage({
            'action': 'askForContent',
            'title': titleWithNameSpace,
            'search': uriComponent,
            'anchorTarget': anchorTarget
        }, [messageChannel.port2]);
    });
}

/**
 * Looks up a Request in a cache and returns a Promise for the matched Response
 * @param {String} cache The name of the cache to look in
 * @param {String} requestUrl The Request URL to fulfill from cache
 * @returns {Promise<Response>} A Promise for the cached Response, or rejects with strings 'disabled' or 'no-match'
 */
function fromCache(cache, requestUrl) {
    // Prevents use of Cache API if user has disabled it
    if (!(useAppCache && cache === APP_CACHE || useAssetsCache && cache === ASSETS_CACHE)) return Promise.reject('disabled');
    return caches.open(cache).then(function (cacheObj) {
        return cacheObj.match(requestUrl).then(function (matching) {
            if (!matching || matching.status === 404) return Promise.reject('no-match');
            console.debug('[SW] Supplying ' + requestUrl + ' from ' + cache + '...');
            return matching;
        });
    });
}

/**
 * Stores or updates in a cache the given Request/Response pair
 * @param {String} cache The name of the cache to open
 * @param {Request|String} request The original Request object or the URL string requested
 * @param {Response} response The Response received from the server/ZIM
 * @returns {Promise} A Promise for the update action
 */
function updateCache(cache, request, response) {
    // Prevents use of Cache API if user has disabled it
    if (!response.ok || !(useAppCache && cache === APP_CACHE || useAssetsCache && cache === ASSETS_CACHE))
        return Promise.resolve();
    return caches.open(cache).then(function (cacheObj) {
        var reqKey = request.url || request;
        console.debug('[SW] Adding ' + reqKey + ' to ' + cache + '...');
        return cacheObj.put(reqKey, response);
    });
}

/**
 * Tests the caching strategy available to this app and if it is Cache API, count the
 * number of assets in ASSETS_CACHE
 * @param {String} url A URL to test against excludedURLSchema
 * @returns {Promise<Array>} A Promise for an array of format [cacheType, cacheDescription, assetCount]
 */
function testCacheAndCountAssets(url) {
    if (regexpExcludedURLSchema.test(url)) return Promise.resolve(['custom', 'custom', 'Custom', '-']);
    if (!useAssetsCache) return Promise.resolve(['none', 'none', 'None', 0]);
    return caches.open(ASSETS_CACHE).then(function (cache) {
        return cache.keys().then(function (keys) {
            return ['cacheAPI', ASSETS_CACHE, 'Cache API', keys.length];
        }).catch(function(err) {
            return err;
        });
    }).catch(function(err) {
        return err;
    });
}
