Fix strftime implementations for format strings "%F" and "%j" (#475)

* fix strftime, %F contains %Y (four digit)

* fix strftime, %j with DST compensation

src/php/datetime/strftime.js

@@ -8,6 +8,11 @@ module.exports = function strftime(fmt, timestamp) {
   //           note 1: Uses global: locutus to store locale info
   //        example 1: strftime("%A", 1062462400); // Return value will depend on date and locale
   //        returns 1: 'Tuesday'
+  //      bugfixed by: Markus Marchewa
+  //        example 2: strftime('%F', 1577836800);
+  //        returns 2: '2020-01-01'
+  //        example 3: (() => {let e = process.env, tz = e.TZ; e.TZ = 'Europe/Vienna'; let r = strftime('%j', 1680307200); e.TZ = tz; return r;})();
+  //        returns 3: '091'
 
   const setlocale = require('../strings/setlocale')
 
@@ -71,10 +76,13 @@ module.exports = function strftime(fmt, timestamp) {
       return _xPad(I === 0 ? 12 : I, 0)
     },
     j: function (d) {
-      let ms = d - new Date('' + d.getFullYear() + '/1/1 GMT')
-      // Line differs from Yahoo implementation which would be
-      // equivalent to replacing it here with:
-      ms += d.getTimezoneOffset() * 60000
+      // calculate the difference between the given date and the start of the year (in localtime), DST shifts may lead
+      // to deltas less than multiples of 24 hours (the day when DST starts has just 23 hours), compensate by adding
+      // the difference between timezone offsets (subtract since values are negative for positive offsets), e.g.:
+      // 2020-05-01 00:00:00 CEST, timezone +0200, offset -120
+      // 2020-01-01 00:00:00 CET , timezone +0100, offset  -60
+      const b = new Date(d.getFullYear(), 0)
+      const ms = d - b - (d.getTimezoneOffset() - b.getTimezoneOffset()) * 60000
       const doy = parseInt(ms / 60000 / 60 / 24, 10) + 1
       return _xPad(doy, 0, 100)
     },
@@ -160,7 +168,7 @@ module.exports = function strftime(fmt, timestamp) {
   const _aggregates = {
     c: 'locale',
     D: '%m/%d/%y',
-    F: '%y-%m-%d',
+    F: '%Y-%m-%d',
     h: '%b',
     n: '\n',
     r: 'locale',

test/generated/php/datetime/test-strftime.js

@@ -16,4 +16,16 @@ describe('src/php/datetime/strftime.js (tested in test/generated/php/datetime/te
     expect(result).to.deep.equal(expected)
     done()
   })
+  it('should pass example 2', function (done) {
+    var expected = '2020-01-01'
+    var result = strftime('%F', 1577836800);
+    expect(result).to.deep.equal(expected)
+    done()
+  })
+  it('should pass example 3', function (done) {
+    var expected = '091'
+    var result = (() => {let e = process.env, tz = e.TZ; e.TZ = 'Europe/Vienna'; let r = strftime('%j', 1680307200); e.TZ = tz; return r;})();
+    expect(result).to.deep.equal(expected)
+    done()
+  })
 })