Fix getUnixTime across dst

package.json

@@ -152,7 +152,7 @@
     "rollup-plugin-cleanup": "3.2.1",
     "rollup-plugin-swc-minify": "1.0.5",
     "serve-static": "1.15.0",
-    "timezone-support": "link:",
+    "timezone-support": "file:",
     "typescript": "4.9.3"
   },
   "keywords": [

src/convert/convert.js

@@ -48,17 +48,25 @@ function getUnixTime (time, timeZone) {
     return epoch
   }
   const unixTime = getUnixTimeFromUTC(time)
+  let convertedUnixTime;
   if (zone) {
     if (timeZone) {
       throw new Error('Both own and other time zones specified. Omit the other one.')
     }
+    convertedUnixTime = unixTime + zone.offset * 60000
   } else {
     if (!timeZone) {
       throw new Error('Missing other time zone.')
     }
     zone = getTransition(unixTime, timeZone)
+    convertedUnixTime = unixTime + zone.offset * 60000
+    const convertedZoneOffset = getTransition(convertedUnixTime, timeZone).offset
+    // check if the converted date may have moved to a different offset (probably because of a DST switch)
+    if (convertedZoneOffset !== zone.offset) {
+      convertedUnixTime = unixTime + convertedZoneOffset * 60000
+    }
   }
-  return unixTime + zone.offset * 60000
+  return convertedUnixTime
 }
 
 function setTimeZone (time, timeZone, options) {

test/getUnixTime.test.js

@@ -84,6 +84,24 @@ it('recognizes daylight-saving time', () => {
   expect(unixTime).toEqual(epoch)
 })
 
+it('recognizes daylight-saving time switch point of explicit timezone', () => {
+  // This test depends on what local TZ it is being executed in!!!
+  // The local TZ has to be at least 2 hours closer to UTC than Melbourne
+  // The TZ where this has been confirmed was UTC+3 (Europe/Sofia)
+  // This test shall fail without the fix because the UTC moment is after the DST switch and the target moment is before that
+  const melbourneTime = {
+    year: 2023,
+    month: 10,
+    day: 1,
+    hours: 0,
+    minutes: 0
+  }
+  const unixTime = getUnixTime(melbourneTime, findTimeZone('Australia/Melbourne'))
+  expect(typeof unixTime === 'number').toBeTruthy()
+  const epoch = Date.UTC(2023, 8, 30, 14, 0)
+  expect(unixTime).toEqual(epoch)
+})
+
 it('checks, that other time zone is specified, if required', () => {
   const berlinTime = {
     year: 2018,