Preserve timezone when modifying DateTime

app/src/main/java/org/tasks/time/DateTime.kt

@@ -52,23 +52,52 @@ class DateTime {
         timeZone = timeZone
     )
 
-    fun startOfMinute(): DateTime = DateTime(millis.startOfMinute())
+    fun startOfMinute(): DateTime = DateTime(millis.startOfMinute(), timeZone)
 
-    fun startOfSecond(): DateTime = DateTime(millis.startOfSecond())
+    fun startOfSecond(): DateTime = DateTime(millis.startOfSecond(), timeZone)
 
-    fun endOfMinute(): DateTime = DateTime(millis.endOfMinute())
+    fun endOfMinute(): DateTime = DateTime(millis.endOfMinute(), timeZone)
 
-    fun noon(): DateTime = DateTime(millis.noon())
+    fun noon(): DateTime = DateTime(
+        year = year,
+        month = monthOfYear,
+        day = dayOfMonth,
+        hour = 12,
+        timeZone = timeZone
+    )
 
-    fun endOfDay(): DateTime = DateTime(millis.endOfDay())
+    fun endOfDay(): DateTime = DateTime(
+        year = year,
+        month = monthOfYear,
+        day = dayOfMonth,
+        hour = 23,
+        minute = 59,
+        second = 59,
+        timeZone = timeZone
+    )
 
-    fun withMillisOfDay(millisOfDay: Int): DateTime = DateTime(millis.withMillisOfDay(millisOfDay))
+    fun withMillisOfDay(millisOfDay: Int): DateTime {
+        val hours = millisOfDay / 3600000
+        val minutes = (millisOfDay % 3600000) / 60000
+        val seconds = (millisOfDay % 60000) / 1000
+        val millis = millisOfDay % 1000
+        return DateTime(
+            year = year,
+            month = monthOfYear,
+            day = dayOfMonth,
+            hour = hours,
+            minute = minutes,
+            second = seconds,
+            millisecond = millis,
+            timeZone = timeZone
+        )
+    }
 
     val offset: Long
         get() = timeZone.getOffset(millis).toLong()
 
     val millisOfDay: Int
-        get() = millis.millisOfDay
+        get() = hourOfDay * 3600000 + minuteOfHour * 60000 + secondOfMinute * 1000 + calendar[Calendar.MILLISECOND]
 
     val year: Int
         get() = calendar[Calendar.YEAR]
@@ -151,11 +180,11 @@ class DateTime {
         return add(Calendar.SECOND, -seconds)
     }
 
-    fun minusDays(days: Int): DateTime = DateTime(millis.minusDays(days))
+    fun minusDays(days: Int): DateTime = add(Calendar.DATE, -days)
 
-    fun minusMinutes(minutes: Int): DateTime = DateTime(millis.minusMinutes(minutes))
+    fun minusMinutes(minutes: Int): DateTime = add(Calendar.MINUTE, -minutes)
 
-    fun minusMillis(millis: Long): DateTime = DateTime(this.millis.minusMillis(millis))
+    fun minusMillis(millis: Long): DateTime = DateTime(this.millis - millis, timeZone)
 
     val isAfterNow: Boolean
         get() = isAfter(currentTimeMillis())

app/src/test/java/org/tasks/time/DateTimeTest.kt

@@ -219,7 +219,9 @@ class DateTimeTest {
     @Test
     fun testMinusMinutes() {
         assertEquals(
-                DateTime(2015, 11, 4, 23, 59, 0), DateTime(2015, 11, 5, 0, 1, 0).minusMinutes(2))
+            DateTime(2015, 11, 4, 23, 59, 0, timeZone = DateTime.UTC),
+            DateTime(2015, 11, 5, 0, 1, 0, timeZone = DateTime.UTC).minusMinutes(2)
+        )
     }
 
     @Test
@@ -292,16 +294,21 @@ class DateTimeTest {
     @Test
     fun testMinusMillis() {
         assertEquals(
-                DateTime(2015, 11, 6, 16, 18, 20, 452),
-                DateTime(2015, 11, 6, 16, 18, 21, 374).minusMillis(922))
+            DateTime(2015, 11, 6, 16, 18, 20, 452, DateTime.UTC),
+            DateTime(2015, 11, 6, 16, 18, 21, 374, DateTime.UTC).minusMillis(922)
+        )
     }
 
     @Test
     fun testMinusDays() {
         assertEquals(
-                DateTime(2015, 11, 6, 16, 19, 16), DateTime(2015, 12, 4, 16, 19, 16).minusDays(28))
+            DateTime(2015, 11, 6, 16, 19, 16, timeZone = DateTime.UTC),
+            DateTime(2015, 12, 4, 16, 19, 16, timeZone = DateTime.UTC).minusDays(28)
+        )
         assertEquals(
-                DateTime(2015, 11, 6, 16, 19, 16), DateTime(2015, 11, 7, 16, 19, 16).minusDays(1))
+            DateTime(2015, 11, 6, 16, 19, 16, timeZone = DateTime.UTC),
+            DateTime(2015, 11, 7, 16, 19, 16, timeZone = DateTime.UTC).minusDays(1)
+        )
     }
 
     @Test
@@ -347,15 +354,17 @@ class DateTimeTest {
     @Test
     fun testStartOfMinute() {
         assertEquals(
-                DateTime(2017, 9, 3, 0, 51, 0, 0),
-                DateTime(2017, 9, 3, 0, 51, 13, 427).startOfMinute())
+            DateTime(2017, 9, 3, 0, 51, 0, 0, DateTime.UTC),
+            DateTime(2017, 9, 3, 0, 51, 13, 427, DateTime.UTC).startOfMinute()
+        )
     }
 
     @Test
     fun testEndOfMinute() {
         assertEquals(
-                DateTime(2017, 9, 22, 14, 47, 59, 999),
-                DateTime(2017, 9, 22, 14, 47, 14, 453).endOfMinute())
+            DateTime(2017, 9, 22, 14, 47, 59, 999, DateTime.UTC),
+            DateTime(2017, 9, 22, 14, 47, 14, 453, DateTime.UTC).endOfMinute()
+        )
     }
 
     @Test
@@ -444,4 +453,28 @@ class DateTimeTest {
             assertEquals(DateTime(2024, 12, 20, timeZone = DateTime.UTC), utcMidnight)
         }
     }
+
+    @Test
+    fun noon() {
+        assertEquals(
+            DateTime(2024, 12, 20, 12, timeZone = DateTime.UTC),
+            DateTime(2024, 12, 20, 8, 30, 45, 123, DateTime.UTC).noon()
+        )
+    }
+
+    @Test
+    fun endOfDay() {
+        assertEquals(
+            DateTime(2024, 12, 20, 23, 59, 59, timeZone = DateTime.UTC),
+            DateTime(2024, 12, 20, 8, 30, 45, 123, DateTime.UTC).endOfDay()
+        )
+    }
+
+    @Test
+    fun millisOfDayRespectsTimezone() {
+        val instant = DateTime(2024, 12, 20, 12, timeZone = DateTime.UTC)
+        val berlinDateTime = DateTime(instant.millis, TimeZone.getTimeZone("Europe/Berlin")) // UTC+1
+        assertEquals(12 * 3600000, instant.millisOfDay)
+        assertEquals(13 * 3600000, berlinDateTime.millisOfDay)
+    }
 }