Improve date and time formatting with fallback for unsupported Intl.DateTimeFormat features (#7099)

* Intl.DateTimeFormat fallback

* only set timezone when available or in config

web/src/utils/dateUtil.ts

@@ -43,31 +43,119 @@ interface DateTimeStyle {
   strftime_fmt: string;
 }
 
+// only used as a fallback if the browser does not support dateStyle/timeStyle in Intl.DateTimeFormat
+const formatMap: {
+  [k: string]: {
+    date: { year: 'numeric' | '2-digit'; month: 'long' | 'short' | '2-digit'; day: 'numeric' | '2-digit' };
+    time: { hour: 'numeric'; minute: 'numeric'; second?: 'numeric'; timeZoneName?: 'short' | 'long' };
+  };
+} = {
+  full: {
+    date: { year: 'numeric', month: 'long', day: 'numeric' },
+    time: { hour: 'numeric', minute: 'numeric', second: 'numeric', timeZoneName: 'long' },
+  },
+  long: {
+    date: { year: 'numeric', month: 'long', day: 'numeric' },
+    time: { hour: 'numeric', minute: 'numeric', second: 'numeric', timeZoneName: 'long' },
+  },
+  medium: {
+    date: { year: 'numeric', month: 'short', day: 'numeric' },
+    time: { hour: 'numeric', minute: 'numeric', second: 'numeric' },
+  },
+  short: { date: { year: '2-digit', month: '2-digit', day: '2-digit' }, time: { hour: 'numeric', minute: 'numeric' } },
+};
+
+/**
+ * Attempts to get the system's time zone using Intl.DateTimeFormat. If that fails (for instance, in environments
+ * where Intl is not fully supported), it calculates the UTC offset for the current system time and returns
+ * it in a string format.
+ *
+ * Keeping the Intl.DateTimeFormat for now, as this is the recommended way to get the time zone.
+ * https://stackoverflow.com/a/34602679
+ *
+ * Intl.DateTimeFormat function as of April 2023, works in 95.03% of the browsers used globally
+ * https://caniuse.com/mdn-javascript_builtins_intl_datetimeformat_resolvedoptions_computed_timezone
+ *
+ * @returns {string} The resolved time zone or a calculated UTC offset.
+ * The returned string will either be a named time zone (e.g., "America/Los_Angeles"), or it will follow
+ * the format "UTC±HH:MM".
+ */
+const getResolvedTimeZone = () => {
+  try {
+    return Intl.DateTimeFormat().resolvedOptions().timeZone;
+  } catch (error) {
+    const offsetMinutes = new Date().getTimezoneOffset();
+    return `UTC${offsetMinutes < 0 ? '+' : '-'}${Math.abs(offsetMinutes / 60)
+      .toString()
+      .padStart(2, '0')}:${Math.abs(offsetMinutes % 60)
+      .toString()
+      .padStart(2, '0')}`;
+  }
+};
+
+/**
+ * Formats a Unix timestamp into a human-readable date/time string.
+ *
+ * The format of the output string is determined by a configuration object passed as an argument, which
+ * may specify a time zone, 12- or 24-hour time, and various stylistic options for the date and time.
+ * If these options are not specified, the function will use system defaults or sensible fallbacks.
+ *
+ * The function is robust to environments where the Intl API is not fully supported, and includes a
+ * fallback method to create a formatted date/time string in such cases.
+ *
+ * @param {number} unixTimestamp - The Unix timestamp to be formatted.
+ * @param {DateTimeStyle} config - User configuration object.
+ * @returns {string} A formatted date/time string.
+ *
+ * @throws {Error} If the given unixTimestamp is not a valid number, the function will return 'Invalid time'.
+ */
 export const formatUnixTimestampToDateTime = (unixTimestamp: number, config: DateTimeStyle): string => {
   const { timezone, time_format, date_style, time_style, strftime_fmt } = config;
   const locale = window.navigator?.language || 'en-us';
-
   if (isNaN(unixTimestamp)) {
     return 'Invalid time';
   }
 
   try {
     const date = new Date(unixTimestamp * 1000);
+    const resolvedTimeZone = getResolvedTimeZone();
 
-    // use strftime_fmt if defined in config file
+    // use strftime_fmt if defined in config
     if (strftime_fmt) {
-      const strftime_locale = strftime.timezone(getUTCOffset(date, timezone || Intl.DateTimeFormat().resolvedOptions().timeZone)).localizeByIdentifier(locale);
+      const offset = getUTCOffset(date, timezone || resolvedTimeZone);
+      const strftime_locale = strftime.timezone(offset).localizeByIdentifier(locale);
       return strftime_locale(strftime_fmt, date);
     }
 
-    // else use Intl.DateTimeFormat
-    const formatter = new Intl.DateTimeFormat(locale, {
+    // DateTime format options
+    const options: Intl.DateTimeFormatOptions = {
       dateStyle: date_style,
       timeStyle: time_style,
-      timeZone: timezone || Intl.DateTimeFormat().resolvedOptions().timeZone,
       hour12: time_format !== 'browser' ? time_format == '12hour' : undefined,
-    });
-    return formatter.format(date);
+    };
+
+    // Only set timeZone option when resolvedTimeZone does not match UTC±HH:MM format, or when timezone is set in config
+    const isUTCOffsetFormat = /^UTC[+-]\d{2}:\d{2}$/.test(resolvedTimeZone);
+    if (timezone || !isUTCOffsetFormat) {
+      options.timeZone = timezone || resolvedTimeZone;
+    }
+
+    const formatter = new Intl.DateTimeFormat(locale, options);
+    const formattedDateTime = formatter.format(date);
+
+    // Regex to check for existence of time. This is needed because dateStyle/timeStyle is not always supported.
+    const containsTime = /\d{1,2}:\d{1,2}/.test(formattedDateTime);
+
+    // fallback if the browser does not support dateStyle/timeStyle in Intl.DateTimeFormat
+    // This works even tough the timezone is undefined, it will use the runtime's default time zone
+    if (!containsTime) {
+      const dateOptions = { ...formatMap[date_style]?.date, timeZone: options.timeZone, hour12: options.hour12 };
+      const timeOptions = { ...formatMap[time_style]?.time, timeZone: options.timeZone, hour12: options.hour12 };
+
+      return `${date.toLocaleDateString(locale, dateOptions)} ${date.toLocaleTimeString(locale, timeOptions)}`;
+    }
+
+    return formattedDateTime;
   } catch (error) {
     return 'Invalid time';
   }
@@ -122,10 +210,19 @@ export const getDurationFromTimestamps = (start_time: number, end_time: number |
  * @returns number of minutes offset from UTC
  */
 const getUTCOffset = (date: Date, timezone: string): number => {
-  const utcDate = new Date(date.getTime() - (date.getTimezoneOffset() * 60 * 1000));
+  // If timezone is in UTC±HH:MM format, parse it to get offset
+  const utcOffsetMatch = timezone.match(/^UTC([+-])(\d{2}):(\d{2})$/);
+  if (utcOffsetMatch) {
+    const hours = parseInt(utcOffsetMatch[2], 10);
+    const minutes = parseInt(utcOffsetMatch[3], 10);
+    return (utcOffsetMatch[1] === '+' ? 1 : -1) * (hours * 60 + minutes);
+  }
+
+  // Otherwise, calculate offset using provided timezone
+  const utcDate = new Date(date.getTime() - date.getTimezoneOffset() * 60 * 1000);
   // locale of en-CA is required for proper locale format
   let iso = utcDate.toLocaleString('en-CA', { timeZone: timezone, hour12: false }).replace(', ', 'T');
   iso += `.${utcDate.getMilliseconds().toString().padStart(3, '0')}`;
   const target = new Date(`${iso}Z`);
-  return  (target.getTime() - utcDate.getTime()) / 60 / 1000;
-}
+  return (target.getTime() - utcDate.getTime()) / 60 / 1000;
+};