wip

Signed-off-by: alperozturk96 <alper_ozturk@proton.me>

Author: alperozturk96

app/build.gradle.kts

@@ -476,7 +476,7 @@ dependencies {
 
     // region iCal4j
     implementation(libs.ical4j) {
-        listOf("org.apache.commons", "commons-logging").forEach { groupName -> exclude(group = groupName) }
+        exclude(group = "commons-logging")
     }
     // endregion
 

app/src/main/java/com/nextcloud/utils/ical/AndroidCompatTimeZoneRegistry.kt

@@ -0,0 +1,51 @@
+/*
+ * Nextcloud - Android Client
+ *
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+package com.nextcloud.utils.ical
+
+import net.fortuna.ical4j.model.TimeZone
+import net.fortuna.ical4j.model.TimeZoneRegistry
+import net.fortuna.ical4j.model.TimeZoneRegistryImpl
+import java.time.ZoneId
+import java.time.zone.ZoneRules
+import java.util.concurrent.ConcurrentHashMap
+
+/**
+ * ical4j 4's default [TimeZoneRegistryImpl.register] publishes every timezone through
+ * [net.fortuna.ical4j.model.ZoneRulesProviderImpl], which extends the platform
+ * [java.time.zone.ZoneRulesProvider]. Both its constructor and
+ * [java.time.zone.ZoneRulesProvider.registerProvider] are blocked hidden APIs on Android and
+ * crash with a NoSuchMethodError.
+ *
+ * This registry keeps timezones defined inside parsed calendars in a local map and delegates
+ * standard timezone lookups to a plain [TimeZoneRegistryImpl], whose read path never touches the
+ * blocked provider.
+ */
+class AndroidCompatTimeZoneRegistry : TimeZoneRegistry {
+
+    private val delegate = TimeZoneRegistryImpl()
+    private val registered = ConcurrentHashMap<String, TimeZone>()
+
+    override fun register(timezone: TimeZone) {
+        registered[timezone.id] = timezone
+    }
+
+    override fun register(timezone: TimeZone, update: Boolean) {
+        register(timezone)
+    }
+
+    override fun clear() {
+        registered.clear()
+    }
+
+    override fun getTimeZone(id: String): TimeZone? = registered[id] ?: delegate.getTimeZone(id)
+
+    override fun getZoneRules(): MutableMap<String, ZoneRules> = delegate.zoneRules
+
+    override fun getZoneId(tzId: String): ZoneId = delegate.getZoneId(tzId)
+
+    override fun getTzId(zoneId: String): String = delegate.getTzId(zoneId)
+}

app/src/main/java/com/nextcloud/utils/ical/AndroidCompatTimeZoneRegistryFactory.kt

@@ -0,0 +1,14 @@
+/*
+ * Nextcloud - Android Client
+ *
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+package com.nextcloud.utils.ical
+
+import net.fortuna.ical4j.model.TimeZoneRegistry
+import net.fortuna.ical4j.model.TimeZoneRegistryFactory
+
+class AndroidCompatTimeZoneRegistryFactory : TimeZoneRegistryFactory() {
+    override fun createRegistry(): TimeZoneRegistry = AndroidCompatTimeZoneRegistry()
+}

app/src/main/resources/ical4j.properties

@@ -1,2 +1,3 @@
 # suppress inspection "UnusedProperty"
 net.fortuna.ical4j.timezone.cache.impl=net.fortuna.ical4j.util.MapTimeZoneCache
+net.fortuna.ical4j.timezone.registry=com.nextcloud.utils.ical.AndroidCompatTimeZoneRegistryFactory