From 1638ded20d2cb26358c5070e995a0d882de82a8c Mon Sep 17 00:00:00 2001
From: DJDavid98 <djdavid98@protonmail.com>
Date: Thu, 16 Sep 2021 21:13:00 +0200
Subject: [PATCH] Give non-misleading labels to Etc/GMT timezone options

Closes #12
---
 src/components/TimestampPicker.tsx | 10 +++++-----
 src/pages/index.tsx                | 24 ++++++++---------------
 src/util/timezone.ts               | 31 ++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 21 deletions(-)
 create mode 100644 src/util/timezone.ts

diff --git a/src/components/TimestampPicker.tsx b/src/components/TimestampPicker.tsx
index 8b766d0..22710ec 100644
--- a/src/components/TimestampPicker.tsx
+++ b/src/components/TimestampPicker.tsx
@@ -2,12 +2,13 @@ import { FontAwesomeIcon } from '@fortawesome/react-fontawesome';
 import { TFunction } from 'i18next';
 import styles from 'modules/TimestampPicker.module.scss';
 import moment, { Moment } from 'moment-timezone';
-import { useCallback, VFC } from 'react';
+import { useCallback, useMemo, VFC } from 'react';
 import Datetime from 'react-datetime';
 import Select from 'react-select';
 import { StylesConfig } from 'react-select/src/styles';
 import { ThemeConfig } from 'react-select/src/theme';
 import { Col, FormGroup, Input, InputGroup, InputGroupAddon, InputGroupText, Label, Row } from 'reactstrap';
+import { getTimezoneValue } from 'src/util/timezone';
 
 const dateInputId = 'date-input';
 const timezoneSelectId = 'timezone-input';
@@ -109,6 +110,8 @@ export const TimestampPicker: VFC<PropTypes> = ({
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   const renderDateInput = useCallback((props: any) => <DateInput {...props} />, []);
 
+  const timezoneSelectValue = useMemo(() => getTimezoneValue(timezone), [timezone]);
+
   return (
     <div className={styles.datepicker}>
       <Row form>
@@ -136,10 +139,7 @@ export const TimestampPicker: VFC<PropTypes> = ({
               </Label>
               <Select
                 inputId={timezoneSelectId}
-                value={{
-                  label: timezone,
-                  value: timezone,
-                }}
+                value={timezoneSelectValue}
                 options={timezoneNames}
                 onChange={handleTimezoneChange}
                 className="w-100"
diff --git a/src/pages/index.tsx b/src/pages/index.tsx
index b68eb45..83c2489 100644
--- a/src/pages/index.tsx
+++ b/src/pages/index.tsx
@@ -10,28 +10,19 @@ import { useCallback, useEffect, useMemo, useState, VFC } from 'react';
 import { SITE_TITLE } from 'src/config';
 import { useLocale } from 'src/util/common';
 import { typedServerSideTranslations } from 'src/util/i18n-server';
+import { getSortedNormalizedTimezoneNames, getTimezoneValue } from 'src/util/timezone';
 
-const forceFirstTimezoneSet = 'GMT';
+interface IndexPageProps {
+  tzNames: string[];
+}
 
-const IndexPage: VFC = () => {
+const IndexPage: VFC<IndexPageProps> = ({ tzNames }) => {
   const {
     t,
     i18n: { language },
   } = useTranslation();
   const locale = useLocale(language);
-  const timezoneNames = useMemo(() => {
-    let compare = (a: string, b: string): number => a.localeCompare(b);
-    try {
-      const collator = new Intl.Collator(undefined, { numeric: true, sensitivity: 'base' });
-      compare = collator.compare;
-    } catch (e) {
-      console.error(e);
-    }
-    return moment.tz
-      .names()
-      .sort((a, b) => (forceFirstTimezoneSet === a ? -1 : forceFirstTimezoneSet === b ? 1 : compare(a, b)))
-      .map((value) => ({ label: value, value }));
-  }, []);
+  const timezoneNames = useMemo(() => tzNames.map((timezone) => getTimezoneValue(timezone)), [tzNames]);
   const [timezone, setTimezone] = useState<string>(() => timezoneNames[0].value);
   const [timestamp, setTimestamp] = useState<Moment>(() => moment(new Date(0)).utc());
   const [inputValue, setInputValue] = useState<Moment | string>('');
@@ -93,8 +84,9 @@ const IndexPage: VFC = () => {
 
 export default IndexPage;
 
-export const getStaticProps: GetStaticProps<SSRConfig> = async ({ locale }) => ({
+export const getStaticProps: GetStaticProps<IndexPageProps & SSRConfig> = async ({ locale }) => ({
   props: {
+    tzNames: getSortedNormalizedTimezoneNames(),
     ...(await typedServerSideTranslations(locale, ['common'])),
   },
 });
diff --git a/src/util/timezone.ts b/src/util/timezone.ts
new file mode 100644
index 0000000..bc3c15c
--- /dev/null
+++ b/src/util/timezone.ts
@@ -0,0 +1,31 @@
+import moment from 'moment-timezone';
+
+export const gmtZoneRegex = /^Etc\/(GMT([+-]\d+)?)$/;
+
+export const switchGmtZoneName = (value: string): string =>
+  value.replace(gmtZoneRegex, (_, extractedIdentifier: string) => extractedIdentifier.replace(/([+-])/, (m) => (m === '+' ? '-' : '+')));
+
+const compareGmtStrings = (a: string, b: string) =>
+  parseInt(a.replace(gmtZoneRegex, '$2'), 10) - parseInt(b.replace(gmtZoneRegex, '$2'), 10);
+
+export const getSortedNormalizedTimezoneNames = (): string[] =>
+  moment.tz
+    .names()
+    .filter((name) => !/^(?:Etc\/)?GMT[+-]0$/.test(name))
+    .sort((a, b) => {
+      const isAGmt = gmtZoneRegex.test(a);
+      const isBGmt = gmtZoneRegex.test(b);
+      if (isAGmt) return isBGmt ? compareGmtStrings(a, b) : -1;
+      if (isBGmt) return isAGmt ? compareGmtStrings(a, b) : 1;
+      return a.localeCompare(b);
+    });
+
+export const getTimezoneLabel = (timezone: string): string => {
+  if (!gmtZoneRegex.test(timezone)) return timezone;
+  return switchGmtZoneName(timezone);
+};
+
+export const getTimezoneValue = (timezone: string) => ({
+  value: timezone,
+  label: getTimezoneLabel(timezone),
+});