// Local Consts
const SW_VERSION = 1;
const SW_CACHE_NAME = "OFFLINE_V1";

// Message Consts
const PURGE_SW_CACHE = "PURGE_SW_CACHE";
const DEL_SW_CACHE = "DEL_SW_CACHE";
const GET_SW_CACHE = "GET_SW_CACHE";
const GET_SW_VERSION = "GET_SW_VERSION";

// Assets
const ASSETS_DOCUMENT = /^\/documents\/[a-zA-Z0-9]{32}\/(cover|file|progress)$/;
const ASSETS_OFFLINE = [
  // Offline Resources
  "/offline",
  "/assets/offline/index.js",
  "/assets/reader/index.js",
  "/assets/images/no-cover.jpg",

  // App Style
  "/manifest.json",
  "/assets/style.css",

  // Reader & Offline Libraries
  "/assets/js/platform.js",
  "/assets/js/jszip.min.js",
  "/assets/js/epub.min.js",
  "/assets/js/no-sleep.js",
  "/assets/js/idb-keyval.js",
];

function wantCache(request) {
  let urlPath = new URL(request.url).pathname;
  if (ASSETS_OFFLINE.includes(urlPath)) return true;
  if (urlPath.match(ASSETS_DOCUMENT)) return true;
  return false;
}

/**
 * Nuke Cache
 **/
function purgeCache() {
  return caches.keys().then(function (names) {
    for (let name of names) caches.delete(name);
  });
}

/**
 * Update Cache
 **/
async function updateCache(request) {
  let cache = await caches.open(SW_CACHE_NAME);

  console.log("UPDATING CACHE:", request.url);

  return fetch(request).then((response) => {
    const resClone = response.clone();
    if (response.status < 400) cache.put(request, resClone);
    return response;
  });
}

/**
 * Pre-Cache Resources on Install
 **/
function cacheOfflineResources() {
  return caches.open(SW_CACHE_NAME).then(function (cache) {
    return cache.addAll(ASSETS_OFFLINE);
  });
}

/**
 * Install & Update Listener -> Cache Offline Resources
 **/
self.addEventListener("install", function (event) {
  console.log("INSTALL:", event);
  event.waitUntil(cacheOfflineResources());
});

/**
 * Message Listener -> Communication Channel Page <-> SW
 **/
self.addEventListener("message", (event) => {
  console.log("MESSAGE:", event);
  let { id, data } = event.data;

  if (data.type === GET_SW_VERSION) {
    event.source.postMessage({ id, data: SW_VERSION });
  } else if (data.type === PURGE_SW_CACHE) {
    purgeCache()
      .then(() => event.source.postMessage({ id, data: "SUCCESS" }))
      .catch(() => event.source.postMessage({ id, data: "FAILURE" }));
  } else if (data.type === GET_SW_CACHE) {
    caches.open(SW_CACHE_NAME).then(async (cache) => {
      let allKeys = await cache.keys();

      let docResources = allKeys
        .map((item) => new URL(item.url).pathname)
        .filter((item) => item.startsWith("/documents/"));

      let documentIDs = Array.from(
        new Set(docResources.map((item) => item.split("/")[2]))
      );

      let cachedDocuments = await Promise.all(
        documentIDs
          .filter(
            (id) =>
              docResources.includes("/documents/" + id + "/file") &&
              docResources.includes("/documents/" + id + "/progress")
          )
          .map(async (id) => {
            let resp = await cache.match("/documents/" + id + "/progress");
            return resp.json();
          })
      );

      event.source.postMessage({ id, data: cachedDocuments });
    });

    // TODO
  } else if (data.type === DEL_SW_CACHE) {
    // TODO
  } else {
    event.source.postMessage({ id, data: { pong: 1 } });
  }
});

/**
 * Fetch Listener -> Cache
 *   - Covers
 *   - Files
 *   - Assets (Styles, JS Libraries)
 *
 * NOTE: We do not cache regular app resources. We will fallback to the
 * offline reader.
 **/
self.addEventListener("fetch", (event) => {
  event.respondWith(
    (async function () {
      // Bypass Lazy Caching
      if (event.request.url.endsWith("/progress")) {
        return updateCache(event.request).catch((e) =>
          caches.match(event.request)
        );
      }

      // Get Potential Cache
      let cachedResponse = await caches.match(event.request);

      // Update Cache Asynchronously (If Wanted)
      let newResponse = (
        wantCache(event.request)
          ? updateCache(event.request)
          : fetch(event.request)
      ).catch((e) => caches.match("/offline"));

      return cachedResponse || newResponse;
    })()
  );
});