Added two new functions dateroll and datediff

lib/date.js

@@ -1,4 +1,7 @@
 'use strict';
+
+const { date } = require('.');
+
 var helpers = module.exports;
 
 /**
@@ -22,3 +25,83 @@ helpers.year = require('year');
  */
 
 helpers.moment = helpers.date = require('helper-date');
+
+helpers.ONE_SEC = 1000;
+helpers.ONE_MIN = helpers.ONE_SEC * 60;
+helpers.ONE_HOUR = helpers.ONE_MIN * 60;
+helpers.ONE_DAY = helpers.ONE_HOUR * 24;
+helpers.ONE_YEAR = helpers.ONE_DAY * 365;
+
+
+helpers.dateroll = function(date1, nUnit, unit, format) {
+  var dateStart = null;
+
+  if ( date1 instanceof Date) {
+    dateStart = date1;
+  } else if ( typeof (date1) === 'string') {
+    dateStart = new Date(date1);
+  }
+
+  var time = dateStart.getTime();
+  var delta = 0;
+
+  if ( unit === 'year' ) {
+    delta = nUnit * helpers.ONE_YEAR;
+  } else if ( unit === 'day' ) {
+    delta = nUnit * helpers.ONE_DAY;
+  } else if ( unit === 'hour' ) {
+    delta = nUnit * helpers.ONE_HOUR;
+  } else if ( unit === 'minute' ) {
+    delta = nUnit * helpers.ONE_MIN;
+  } else if ( unit === 'second' ) {
+    delta = nUnit * helpers.ONE_SEC;
+  }
+
+  time = time + delta;
+
+  var d = new Date();
+  d.setTime(time);
+
+  var formattedDate = '';
+
+  if ( typeof (format) === 'string' && format  ) {
+    formattedDate = format.replace('yyyy', d.getUTCFullYear()).replace('MM', ('0'+(d.getUTCMonth()+1)).slice(-2)).replace('dd', ('0' + d.getUTCDate()).slice(-2))
+  } else {
+    formattedDate = + d.getUTCFullYear() + '-' + ('0'+(d.getUTCMonth()+1)).slice(-2) + '-' +
+    ('0' + d.getUTCDate()).slice(-2);
+  }
+
+  return formattedDate;
+};
+
+helpers.datediff = function(date1, date2, unit) {
+  let dateFrom= null;
+  let dateTo = null; 
+  if ( date1 instanceof Date ) {
+    dateFrom = date1 ;
+  } else if ( typeof (date1) === 'string' ) {
+    dateFrom = new Date(date1);
+  }
+
+  if ( date2 instanceof Date ) {
+    dateTo = date2 ;
+  } else if (typeof (date2) === 'string') {
+    dateTo = new Date(date2);
+  }
+
+  var delta = dateTo.getTime() - dateFrom.getTime();
+
+  if ( unit === 'year' ) {
+    return delta / helpers.ONE_YEAR;
+  } else if ( unit === 'day') {
+    return delta / helpers.ONE_DAY;
+  } else if ( unit === 'hour') {
+    return delta / helpers.ONE_HOUR;
+  } else if ( unit === 'minute') {
+    return delta / helpers.ONE_MIN;
+  } else if ( unit === 'second') {
+    return delta / helpers.ONE_SEC;
+  } else {
+    return delta / helpers.ONE_DAY;
+  }
+};

test/date.js

@@ -0,0 +1,29 @@
+'use strict';
+
+require('mocha');
+var assert = require('assert');
+var hbs = require('handlebars').create();
+var helpers = require('..');
+helpers.date({handlebars: hbs});
+
+describe('date', function() {
+  describe('datediff', function() {
+    describe('inline or subexpression', function() {
+      it('should return the difference of two numbers.', function() {
+        var fn = hbs.compile('{{datediff dateFrom dateTo unit}}');
+        var r = fn({dateFrom: '2022-01-01', dateTo: '2023-01-01', unit: 'year'});
+        console.log("Result: " + r);
+        assert.equal(r, '1');
+      });
+    });
+  });
+
+  describe('datedroll', function() {
+    describe('inline', function() {
+      it('should return the computed date.', function() {
+        var fn = hbs.compile('{{dateroll dateFrom nUnit unit}}');
+        assert.equal(fn({dateFrom: '2022-01-01', nUnit: 365, unit: 'day', format: 'yyyy-MM-dd'}), '2023-01-01');
+      });
+    });
+  });
+});