/*
 * Offline copy of the public calculator (field staff often have weak signal).
 *  - The calculator page: network first (fresh parameters), stored copy when
 *    offline or slow. Responses marked no-store (admin views) are never kept.
 *  - Versioned assets (assets/...?v=): stored copy first.
 *  - calc.php, admin/ and everything else: network only, never stored.
 */
'use strict';
var CACHE = 'serubi-v1';
var PAGE_TIMEOUT_MS = 4000;
var SCOPE = self.registration.scope;          // e.g. https://host/ or http://localhost/calcserubi-prod/
var PAGE_KEY = SCOPE;                         // one stored copy of the calculator, whatever the query string

self.addEventListener('install', function () { self.skipWaiting(); });

self.addEventListener('activate', function (event) {
  event.waitUntil(caches.keys().then(function (keys) {
    return Promise.all(keys.filter(function (k) { return k !== CACHE; }).map(function (k) { return caches.delete(k); }));
  }).then(function () { return self.clients.claim(); }));
});

function isCalculatorPage(url) {
  var rel = url.href.slice(SCOPE.length).split('?')[0];
  return rel === '' || rel === 'index.php';
}

function storable(res) {
  return res && res.ok && res.type === 'basic' && !/no-store/i.test(res.headers.get('Cache-Control') || '');
}

function pageNetworkFirst(request) {
  return caches.open(CACHE).then(function (cache) {
    var network = fetch(request).then(function (res) {
      if (storable(res)) cache.put(PAGE_KEY, res.clone());
      return res;
    });
    network.catch(function () { /* handled below */ });
    var timeout = new Promise(function (resolve) { setTimeout(resolve, PAGE_TIMEOUT_MS); });
    // slow network: answer from the stored copy after the timeout, if there is one
    return Promise.race([network, timeout.then(function () { return cache.match(PAGE_KEY).then(function (c) { return c || network; }); })])
      .catch(function () { return cache.match(PAGE_KEY).then(function (c) { if (c) return c; throw new Error('offline'); }); });
  });
}

function assetCacheFirst(request) {
  return caches.open(CACHE).then(function (cache) {
    return cache.match(request).then(function (hit) {
      if (hit) return hit;
      return fetch(request).then(function (res) {
        if (storable(res)) {
          // keep only the newest version (?v=) of each asset
          var path = new URL(request.url).pathname;
          cache.keys().then(function (keys) {
            keys.forEach(function (k) { if (new URL(k.url).pathname === path && k.url !== request.url) cache.delete(k); });
          });
          cache.put(request, res.clone());
        }
        return res;
      });
    });
  });
}

self.addEventListener('fetch', function (event) {
  var req = event.request;
  if (req.method !== 'GET') return;
  var url = new URL(req.url);
  if (url.origin !== self.location.origin || req.url.indexOf(SCOPE) !== 0) return;
  if (req.mode === 'navigate' && isCalculatorPage(url)) {
    event.respondWith(pageNetworkFirst(req));
  } else if (url.pathname.indexOf('/assets/') !== -1) {
    event.respondWith(assetCacheFirst(req));
  }
  // anything else (calc.php, admin/, ...) goes straight to the network
});