Readme.md

TW Leave Balance Calculator v 0.0.1

Steps:

1. Install Tampermonkey
2. Add scripts to Tampermonkey
3. Go to https://na32.salesforce.com/a1W?rlid=00N50000002ejrH&id=a0y50000000onx0
4. Insert your join date (which you could find in Jigsaw)
5. Enjoy your automatic leave balance calculation

LeaveBalanceCalculator.js

// ==UserScript==
// @name         Leave Balance Calculator
// @namespace    
// @version      0.0.1
// @description  
// @author       Sam
// @match        https://na32.salesforce.com/a1W?rlid=00N50000002ejrH&id=a0y50000000onx0
// @grant        none
// ==/UserScript==

var AvailableLeaveCalculator = {
  calculate: function(joinDate, currentDate, leavesTaken) {
    var monthSinceJoin = Math.floor((currentDate - joinDate)  / (1000  * 3600 * 24 * 30) + 1);
    var availableLeavesPerYear = 20;
    var accruedLeaves = monthSinceJoin * (availableLeavesPerYear / 12);
    var availableLeaves = accruedLeaves - leavesTaken;
    return availableLeaves;    
  }
}

var NodeListUtility = {
  toArray: function(nodeList){
    return Array.prototype.slice.call(nodeList);
  }
};

var AnnualLeavePage = function(){
  this._leaveCalculatorContainer = document.createElement("div");
  var container = document.getElementById("bodyCell");
  container.insertBefore(this._leaveCalculatorContainer, container.firstChild);

  this.displayJoinDateForm = function(){
    var form = document.createElement("form");
    form.innerHTML = "\
      Join date : <input id='joinDate' type='date'/> \
      <input type='submit'/>\
    ";
    this._leaveCalculatorContainer.appendChild(form);
    return form;
  };

  this.getLeavesTakenTotal = function(){
    var leavesTakenRowNodes = document.querySelectorAll(".list .dataRow td:nth-child(8)");
    var leavesTakenRowArray = NodeListUtility.toArray(leavesTakenRowNodes);
    var leavesTakenTotal = leavesTakenRowArray.map(function(element){return element.innerHTML;})
                                  .map(function(number){return parseFloat(number);})
                                  .reduce(function(sum, element){return sum + element;}, 0);
    return leavesTakenTotal;
  };

  this.displayAvailableLeaves = function(availableLeaves){
    this._leaveCalculatorContainer.innerHTML = "\
      <h1>\
         Your Leave Balance is " + availableLeaves.toFixed(2) + " day(s) \
      <h1>";
  };
};

var AnnualLeaveExtension = function(_page){
  var page = _page;

  this._getJoinDate = function(){
    return new Promise(function (resolve) {
      var savedJoinDate = window.localStorage.getItem("joinDate");
      if (!!savedJoinDate) {
        resolve(new Date(savedJoinDate));
      } else {
        var form = page.displayJoinDateForm();
        form.addEventListener("submit", function(event){
          event.preventDefault()
          var joinDate = new Date(document.getElementById("joinDate").value);
          window.localStorage.setItem("joinDate", joinDate);
          resolve(joinDate);
        });
      }
    });
  };

  this.run = function(){
    this._getJoinDate()
      .then(function(joinDate) {
        var leavesTaken = page.getLeavesTakenTotal();
        var availableLeaves = AvailableLeaveCalculator.calculate(joinDate,  new Date(), leavesTaken);
        page.displayAvailableLeaves(availableLeaves);  
      });
  };
};

new AnnualLeaveExtension(new AnnualLeavePage()).run();