Split time builder into start and end time builders (#102)

* [WIP] Split TimeFieldsBuilder into StartTimeBuilder and EndTimeBuilder; make operation more clear

* [WIP] Continue with EndTimeBuilder; drop TimeFieldsBuilder

* [WIP] Naming changes

* Finish EndTimeBuilder

* Add DurationBuilder and update EndTimeBuilder for recurring events

- Add DurationBuilder to handle duration for recurring events
- Update EndTimeBuilder to skip DTEND for recurring events
- Add unit tests for both builders
- Fix Duration.toRfc5545Duration() for zero seconds

* Refactor DurationBuilder to remove debug print and use Duration.ZERO

- Remove the `System.err.println` statement that prints `startDate` and `endDate`.
- Replace `java.time.Duration.ofSeconds(0)` with `java.time.Duration.ZERO`

* Add / refactor tests

Author: rfc2822

lib/src/androidTest/kotlin/at/bitfire/synctools/mapping/calendar/LegacyAndroidEventBuilder2Test.kt

@@ -56,6 +56,22 @@ class AndroidCalendarProviderBehaviorTest {
     }
 
 
+    @Test
+    fun testInsertEventWithDurationZeroSeconds() {
+        // To make sure that it's not a problem to insert a recurring event with a duration of zero seconds.
+        val values = contentValuesOf(
+            Events.CALENDAR_ID to calendar.id,
+            Events.DTSTART to 1759403653000,    // Thu Oct 02 2025 11:14:13 GMT+0000
+            Events.DURATION to "PT0S",
+            Events.TITLE to "Event with useless RRULE",
+            Events.RRULE to "FREQ=DAILY;UNTIL=20251002T000000Z"
+        )
+        val id = calendar.addEvent(Entity(values))
+
+        val event2 = calendar.getEventRow(id)
+        assertContentValuesEqual(values, event2!!, onlyFieldsInExpected = true)
+    }
+
     @Test
     fun testInsertEventWithRRuleUntilBeforeDtStart() {
         // To make sure that's not a problem to insert an (invalid/useless) RRULE with UNTIL before the event's DTSTART.

lib/src/androidTest/kotlin/at/bitfire/synctools/storage/calendar/AndroidCalendarProviderBehaviorTest.kt

@@ -6,6 +6,7 @@
 
 package at.bitfire.ical4android
 
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.Css3Color
 import net.fortuna.ical4j.model.Parameter
 import net.fortuna.ical4j.model.Property
@@ -91,4 +92,7 @@ data class Event(
             return email
         }
 
+    fun requireDtStart(): DtStart =
+        dtStart ?: throw InvalidICalendarException("Missing DTSTART in VEVENT")
+
 }

lib/src/main/kotlin/at/bitfire/ical4android/Event.kt

@@ -8,7 +8,7 @@ package at.bitfire.ical4android
 
 import at.bitfire.ical4android.ICalendar.Companion.CALENDAR_NAME
 import at.bitfire.synctools.BuildConfig
-import at.bitfire.synctools.exception.InvalidRemoteResourceException
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.ICalendarParser
 import at.bitfire.synctools.icalendar.validation.ICalPreprocessor
 import net.fortuna.ical4j.data.CalendarBuilder
@@ -89,7 +89,7 @@ open class ICalendar {
          *
          * @return parsed iCalendar resource
          *
-         * @throws InvalidRemoteResourceException when the iCalendar can't be parsed
+         * @throws InvalidICalendarException when the iCalendar can't be parsed
          */
         @Deprecated("Use ICalendarParser directly")
         fun fromReader(

lib/src/main/kotlin/at/bitfire/ical4android/ICalendar.kt

@@ -14,7 +14,7 @@ import android.os.ParcelFileDescriptor
 import android.util.Base64
 import androidx.core.content.contentValuesOf
 import at.bitfire.ical4android.ICalendar.Companion.withUserAgents
-import at.bitfire.synctools.exception.InvalidRemoteResourceException
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.Css3Color
 import at.bitfire.synctools.storage.BatchOperation
 import at.bitfire.synctools.storage.JtxBatchOperation
@@ -285,7 +285,7 @@ open class JtxICalObject(
          *
          * @return array of filled [JtxICalObject] data objects (may have size 0)
          *
-         * @throws InvalidRemoteResourceException when the iCalendar can't be parsed
+         * @throws InvalidICalendarException when the iCalendar can't be parsed
          * @throws IOException on I/O errors
          */
         fun fromReader(

lib/src/main/kotlin/at/bitfire/ical4android/JtxICalObject.kt

@@ -8,7 +8,7 @@ package at.bitfire.ical4android
 
 import androidx.annotation.IntRange
 import at.bitfire.ical4android.util.DateUtils
-import at.bitfire.synctools.exception.InvalidRemoteResourceException
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.Css3Color
 import net.fortuna.ical4j.data.CalendarOutputter
 import net.fortuna.ical4j.model.Calendar
@@ -107,7 +107,7 @@ data class Task(
          *
          * @return array of filled [Task] data objects (may have size 0)
          *
-         * @throws InvalidRemoteResourceException when the iCalendar can't be parsed
+         * @throws InvalidICalendarException when the iCalendar can't be parsed
          * @throws IOException on I/O errors
          */
         fun tasksFromReader(reader: Reader): List<Task> {

lib/src/main/kotlin/at/bitfire/ical4android/Task.kt

@@ -42,7 +42,7 @@ object AndroidTimeUtils {
     /**
      * Timezone ID to store for all-day events, according to CalendarContract.Events SDK documentation.
      */
-    val TZID_ALLDAY = "UTC"
+    val TZID_UTC = "UTC"
 
     private const val RECURRENCE_LIST_TZID_SEPARATOR = ';'
     private const val RECURRENCE_LIST_VALUE_SEPARATOR = ","
@@ -136,7 +136,7 @@ object AndroidTimeUtils {
                 }
             } else
                 // DATE
-                TZID_ALLDAY
+                TZID_UTC
 
 
     // recurrence sets

lib/src/main/kotlin/at/bitfire/ical4android/util/AndroidTimeUtils.kt

@@ -152,7 +152,7 @@ object TimeApiExtensions {
             var secs = seconds
 
             if (secs == 0L)
-                return "P0S"
+                return "PT0S"
 
             var weeks = secs / SECONDS_PER_WEEK
             secs -= weeks * SECONDS_PER_WEEK

lib/src/main/kotlin/at/bitfire/ical4android/util/TimeApiExtensions.kt

@@ -7,9 +7,9 @@
 package at.bitfire.synctools.exception
 
 /**
- * Represents an invalid remote resource (for instance, a calendar object resource).
+ * Represents an invalid iCalendar resource.
  */
-class InvalidRemoteResourceException: InvalidResourceException {
+class InvalidICalendarException: InvalidResourceException {
 
     constructor(message: String): super(message)
     constructor(message: String, ex: Throwable): super(message, ex)

…eption/InvalidRemoteResourceException.kt …s/exception/InvalidICalendarException.ktlib/src/main/kotlin/at/bitfire/synctools/exception/InvalidRemoteResourceException.kt renamed to lib/src/main/kotlin/at/bitfire/synctools/exception/InvalidICalendarException.kt lib/src/main/kotlin/at/bitfire/synctools/exception/InvalidRemoteResourceException.kt renamed to lib/src/main/kotlin/at/bitfire/synctools/exception/InvalidICalendarException.kt

@@ -6,7 +6,7 @@
 
 package at.bitfire.synctools.icalendar
 
-import at.bitfire.synctools.exception.InvalidRemoteResourceException
+import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.validation.ICalPreprocessor
 import net.fortuna.ical4j.data.CalendarBuilder
 import net.fortuna.ical4j.data.CalendarParserFactory
@@ -39,7 +39,7 @@ class ICalendarParser(
      * @param reader        where the iCalendar is read from
      * @param tzRegistry    time zone registry where VTIMEZONE definitions of the iCalendar will be put
      *
-     * @throws InvalidRemoteResourceException   when the resource is can't be parsed
+     * @throws InvalidICalendarException   when the resource is can't be parsed
      */
     fun parse(reader: Reader): Calendar {
         // preprocess stream to work around problems that prevent parsing and thus can't be fixed later
@@ -54,9 +54,9 @@ class ICalendarParser(
                 /* tzRegistry = */ TimeZoneRegistryFactory.getInstance().createRegistry()
             ).build(preprocessed)
         } catch(e: ParserException) {
-            throw InvalidRemoteResourceException("Couldn't parse iCalendar", e)
+            throw InvalidICalendarException("Couldn't parse iCalendar", e)
         } catch(e: IllegalArgumentException) {
-            throw InvalidRemoteResourceException("iCalendar contains invalid value", e)
+            throw InvalidICalendarException("iCalendar contains invalid value", e)
         }
 
         // Pre-process calendar for increased compatibility (fixes some common errors)