Guess timezone from CreateDate if OffsetTimeDigitized is not present

This should help alleviate the problem that
#319 is trying to
solve. Note that it's not foolproof, due to the inherent ambiguity of
expressing times without timezones. Specifically, photos taken during
the hour that occurs twice when we switch from EDT to EST, may not have
the correct timezone applied.

Most of the code in timezone.js came from https://www.codeproject.com/articles/58728/javascript-code-to-determine-when-daylight-savings

src/routes/home/Home.js

@@ -46,6 +46,7 @@ import s from './Home.css';
 
 import SubmissionDetails from '../../components/SubmissionDetails.js';
 import { isImage, isVideo } from '../../isImage.js';
+import { getNycTimezoneOffset } from '../../timezone.js';
 
 const GOOGLE_MAPS_API_KEY = 'AIzaSyDlwm2ykA0ohTXeVepQYvkcmdjz2M2CKEI';
 
@@ -141,6 +142,7 @@ async function extractLocation({ attachmentFile, attachmentArrayBuffer, ext }) {
 }
 
 async function extractDate({ attachmentFile, attachmentArrayBuffer, ext }) {
+  debugger;
   try {
     if (isVideo({ ext })) {
       return extractLocationDateFromVideo({ attachmentArrayBuffer })[1];
@@ -163,7 +165,8 @@ async function extractDate({ attachmentFile, attachmentArrayBuffer, ext }) {
       millisecondsSinceEpoch: CreateDate.getTime(),
       offset: OffsetTimeDigitized
         ? parseInt(OffsetTimeDigitized, 10) * -60
-        : new Date().getTimezoneOffset(),
+        : getNycTimezoneOffset(CreateDate)
+        // : new Date().getTimezoneOffset(),
     };
   } catch (err) {
     console.error(err.stack);

src/timezone.js

@@ -0,0 +1,116 @@
+function DisplayDstSwitchDates()
+{
+  var year = new Date().getYear();
+  if (year < 1000)
+    year += 1900;
+
+  var firstSwitch = 0;
+  var secondSwitch = 0;
+  var lastOffset = 99;
+
+  // Loop through every month of the current year
+  for (let i = 0; i < 12; i++)
+  {
+    // Fetch the timezone value for the month
+    var newDate = new Date(Date.UTC(year, i, 0, 0, 0, 0, 0));
+    var tz = -1 * newDate.getTimezoneOffset() / 60;
+
+    // Capture when a timzezone change occurs
+    if (tz > lastOffset)
+      firstSwitch = i-1;
+    else if (tz < lastOffset)
+      secondSwitch = i-1;
+
+    lastOffset = tz;
+  }
+
+  // Go figure out date/time occurrences a minute before
+  // a DST adjustment occurs
+  var secondDstDate = FindDstSwitchDate(year, secondSwitch);
+  var firstDstDate = FindDstSwitchDate(year, firstSwitch);
+
+  return {firstDstDate, secondDstDate};
+}
+
+function FindDstSwitchDate(year, month)
+{
+  // Set the starting date
+  var baseDate = new Date(Date.UTC(year, month, 0, 0, 0, 0, 0));
+  var changeDay = 0;
+  var changeMinute = -1;
+  var baseOffset = -1 * baseDate.getTimezoneOffset() / 60;
+  var dstDate;
+
+  // Loop to find the exact day a timezone adjust occurs
+  for (let day = 0; day < 50; day++)
+  {
+    var tmpDate = new Date(Date.UTC(year, month, day, 0, 0, 0, 0));
+    var tmpOffset = -1 * tmpDate.getTimezoneOffset() / 60;
+
+    // Check if the timezone changed from one day to the next
+    if (tmpOffset != baseOffset)
+    {
+      var minutes = 0;
+      changeDay = day;
+
+      // Back-up one day and grap the offset
+      tmpDate = new Date(Date.UTC(year, month, day-1, 0, 0, 0, 0));
+      tmpOffset = -1 * tmpDate.getTimezoneOffset() / 60;
+
+      // Count the minutes until a timezone change occurs
+      while (changeMinute == -1)
+      {
+        tmpDate = new Date(Date.UTC(year, month, day-1, 0, minutes, 0, 0));
+        tmpOffset = -1 * tmpDate.getTimezoneOffset() / 60;
+
+        // Determine the exact minute a timezone change
+        // occurs
+        if (tmpOffset != baseOffset)
+        {
+          // Back-up a minute to get the date/time just
+          // before a timezone change occurs
+          tmpOffset = new Date(Date.UTC(year, month,
+            day-1, 0, minutes-1, 0, 0));
+          changeMinute = minutes;
+          break;
+        }
+        else
+          minutes++;
+      }
+
+      // Add a month (for display) since JavaScript counts
+      // months from 0 to 11
+      dstDate = tmpOffset.getMonth() + 1;
+
+      // Pad the month as needed
+      if (dstDate < 10) dstDate = "0" + dstDate;
+
+      // Add the day and year
+      dstDate += '/' + tmpOffset.getDate() + '/' + year + ' ';
+
+      // Capture the time stamp
+      tmpDate = new Date(Date.UTC(year, month,
+        day-1, 0, minutes-1, 0, 0));
+      dstDate += tmpDate.toTimeString().split(' ')[0];
+      return dstDate;
+    }
+  }
+}
+
+function isDst(date) {
+  const result = DisplayDstSwitchDates()
+  // console.log(result)
+
+  const { firstDstDate, secondDstDate } = result
+  const from = new Date(firstDstDate)
+  const to = new Date(secondDstDate)
+  const now = new Date();
+  const isDst = from.getTime() < now.getTime() && now.getTime() < to.getTime()
+  // console.log({isDst})
+
+  return isDst;
+}
+
+export function getNycTimezoneOffset(date) {
+  return isDst(date) ? -240 : -300
+}