cookies: Refactor `pad_cookie.js`

* Use the cookie functions from `pad_utils.js`.
  * Delete unused methods, variables, and parameters.
  * Simplify the logic.
  * Use an ES6 class instead of a weird literal thingy.
  * Use `const` instead of `var`.

src/static/js/pad_cookie.js

@@ -1,9 +1,3 @@
-/**
- * This code is mostly from the old Etherpad. Please help us to comment this code.
- * This helps other people to understand this code better and helps them to improve it.
- * TL;DR COMMENTS ON THIS FILE ARE HIGHLY APPRECIATED
- */
-
 /**
  * Copyright 2009 Google Inc.
  *
@@ -20,130 +14,51 @@
  * limitations under the License.
  */
 
+const createCookie = require('./pad_utils').createCookie;
+const readCookie = require('./pad_utils').readCookie;
 
-var padcookie = (function()
-{
-  var cookieName = isHttpsScheme() ? "prefs" : "prefsHttp";
-
-  function getRawCookie()
-  {
-    // returns null if can't get cookie text
-    if (!document.cookie)
-    {
-      return null;
-    }
-    // look for (start of string OR semicolon) followed by whitespace followed by prefs=(something);
-    var regexResult = document.cookie.match(new RegExp("(?:^|;)\\s*" + cookieName + "=([^;]*)(?:;|$)"));
-    if ((!regexResult) || (!regexResult[1]))
-    {
-      return null;
-    }
-    return regexResult[1];
+exports.padcookie = new class {
+  constructor() {
+    this.cookieName_ = window.location.protocol === 'https:' ? 'prefs' : 'prefsHttp';
+    const prefs = this.readPrefs_() || {};
+    delete prefs.userId;
+    delete prefs.name;
+    delete prefs.colorId;
+    this.prefs_ = prefs;
+    this.savePrefs_();
   }
 
-  function setRawCookie(safeText)
-  {
-    var expiresDate = new Date();
-    expiresDate.setFullYear(3000);
-    var secure = isHttpsScheme() ? ";secure" : "";
-    var sameSite = isHttpsScheme() ?  ";sameSite=Strict": ";sameSite=Lax";
-    document.cookie = (cookieName + "=" + safeText + ";expires=" + expiresDate.toGMTString() + secure + sameSite);
-  }
-
-  function parseCookie(text)
-  {
-    // returns null if can't parse cookie.
-    try
-    {
-      var cookieData = JSON.parse(unescape(text));
-      return cookieData;
-    }
-    catch (e)
-    {
-      return null;
-    }
-  }
-
-  function stringifyCookie(data)
-  {
-    return escape(JSON.stringify(data));
-  }
-
-  function saveCookie()
-  {
-    if (!inited)
-    {
-      return;
-    }
-    setRawCookie(stringifyCookie(cookieData));
-
-    if ((!getRawCookie()) && (!alreadyWarnedAboutNoCookies))
-    {
+  init() {
+    if (this.readPrefs_() == null) {
       $.gritter.add({
-        title: "Error",
-        text: html10n.get("pad.noCookie"),
+        title: 'Error',
+        text: html10n.get('pad.noCookie'),
         sticky: true,
-        class_name: "error"
+        class_name: 'error',
       });
-      alreadyWarnedAboutNoCookies = true;
     }
   }
 
-  function isHttpsScheme() {
-    return window.location.protocol == "https:";
+  readPrefs_() {
+    const jsonEsc = readCookie(this.cookieName_);
+    if (jsonEsc == null) return null;
+    try {
+      return JSON.parse(unescape(jsonEsc));
+    } catch (e) {
+      return null;
+    }
   }
 
-  var wasNoCookie = true;
-  var cookieData = {};
-  var alreadyWarnedAboutNoCookies = false;
-  var inited = false;
+  savePrefs_() {
+    createCookie(this.cookieName_, escape(JSON.stringify(this.prefs_)), 365 * 100);
+  }
 
-  var pad = undefined;
-  var self = {
-    init: function(prefsToSet, _pad)
-    {
-      pad = _pad;
+  getPref(prefName) {
+    return this.prefs_[prefName];
+  }
 
-      var rawCookie = getRawCookie();
-      if (rawCookie)
-      {
-        var cookieObj = parseCookie(rawCookie);
-        if (cookieObj)
-        {
-          wasNoCookie = false; // there was a cookie
-          delete cookieObj.userId;
-          delete cookieObj.name;
-          delete cookieObj.colorId;
-          cookieData = cookieObj;
-        }
-      }
-
-      for (var k in prefsToSet)
-      {
-        cookieData[k] = prefsToSet[k];
-      }
-
-      inited = true;
-      saveCookie();
-    },
-    wasNoCookie: function()
-    {
-      return wasNoCookie;
-    },
-    isCookiesEnabled: function() {
-      return !!getRawCookie();
-    },
-    getPref: function(prefName)
-    {
-      return cookieData[prefName];
-    },
-    setPref: function(prefName, value)
-    {
-      cookieData[prefName] = value;
-      saveCookie();
-    }
-  };
-  return self;
-}());
-
-exports.padcookie = padcookie;
+  setPref(prefName, value) {
+    this.prefs_[prefName] = value;
+    this.savePrefs_();
+  }
+}();