From e48bebdc6755b488bf07f5ba3f21c2c06cd49690 Mon Sep 17 00:00:00 2001
From: Jumaru <karoloskonst@gmail.com>
Date: Fri, 3 Dec 2021 18:38:14 -0500
Subject: [PATCH] Timezone issue

---
 src/plugin/timezone/index.js | 13 ++++++++++++-
 src/plugin/utc/index.js      |  3 +++
 test/timezone.test.js        |  9 +++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/plugin/timezone/index.js b/src/plugin/timezone/index.js
index c8f8a4675..6ef0d5d82 100644
--- a/src/plugin/timezone/index.js
+++ b/src/plugin/timezone/index.js
@@ -92,6 +92,17 @@ export default (o, c, d) => {
 
   const proto = c.prototype
 
+  const oldAdd = proto.add
+  proto.add = function (number, units) {
+    if (!this.$x || !this.$x.$timezone) {
+      return oldAdd.call(this, number, units)
+    }
+
+    const withoutTz = d(this.valueOf())
+    const addWithoutTz = oldAdd.call(withoutTz, number, units)
+    return addWithoutTz.tz(this.$x.$timezone)
+  }
+
   proto.tz = function (timezone = defaultTimezone, keepLocalTime) {
     const oldOffset = this.utcOffset()
     const date = this.toDate()
@@ -99,11 +110,11 @@ export default (o, c, d) => {
     const diff = Math.round((date - new Date(target)) / 1000 / 60)
     let ins = d(target).$set(MS, this.$ms)
       .utcOffset((-Math.round(date.getTimezoneOffset() / 15) * 15) - diff, true)
+    ins.$x.$timezone = timezone
     if (keepLocalTime) {
       const newOffset = ins.utcOffset()
       ins = ins.add(oldOffset - newOffset, MIN)
     }
-    ins.$x.$timezone = timezone
     return ins
   }
 
diff --git a/src/plugin/utc/index.js b/src/plugin/utc/index.js
index 10ff1ec9a..afe8971d4 100644
--- a/src/plugin/utc/index.js
+++ b/src/plugin/utc/index.js
@@ -89,8 +89,11 @@ export default (option, Dayjs, dayjs) => {
     const offset = Math.abs(input) <= 16 ? input * 60 : input
     let ins = this
     if (keepLocalTime) {
+      const localTimezoneOffset = this.$u
+        ? this.toDate().getTimezoneOffset() : -1 * this.utcOffset()
       ins.$offset = offset
       ins.$u = input === 0
+      ins.$x.$localOffset = localTimezoneOffset
       return ins
     }
     if (input !== 0) {
diff --git a/test/timezone.test.js b/test/timezone.test.js
index 58e83d225..984ebd0d1 100644
--- a/test/timezone.test.js
+++ b/test/timezone.test.js
@@ -15,6 +15,15 @@ afterEach(() => {
   MockDate.reset()
 })
 
+it('Parse timezones', () => {
+  expect(dayjs('2021-07-07').tz('Europe/London').startOf('week').format('HH:mm')).toBe('00:00')
+  expect(dayjs('2021-12-12').tz('Europe/London').startOf('week').format('HH:mm')).toBe('00:00')
+
+  expect(dayjs('2013-11-18 11:00').tz('Europe/London').add(-300, 'minute').valueOf()).toBe(dayjs('2013-11-18 11:00').add(-300, 'minute').valueOf())
+  expect(dayjs('2013-11-18 11:00').tz('Europe/London').format('HH:mm')).toBe('16:00')
+  expect(dayjs('2013-11-18 11:00').tz('Europe/London').add(-300, 'minute').format('HH:mm')).toBe('11:00')
+})
+
 it('Add Time days (DST)', () => {
   // change timezone before running test
   // New Zealand (-720)