Help the polymorphic decoder determine the Serializer to use by alway…

…s putting the type discriminator first

common/src/main/kotlin/de/sipgate/federmappe/common/StringMapToObjectDecoder.kt

@@ -100,8 +100,8 @@ class StringMapToObjectDecoder(
         super.endStructure(descriptor)
     }
 
+    @Suppress("UNCHECKED_CAST")
     override fun <T> decodeType(typeKey: String): T? {
-        @Suppress("UNCHECKED_CAST")
         val currentData = (data[key] as? Map<String, Any>) ?: return null
         return (currentData[typeKey] as? T)
     }

realtimedb/src/main/kotlin/de/sipgate/federmappe/realtimedb/DataSnapshotExt.kt

@@ -24,9 +24,27 @@ inline fun <reified T : Any> DataSnapshot.toObjectWithSerializer(
     customSerializers: SerializersModule = EmptySerializersModule()
 ): T = serializer.deserialize(StringMapToObjectDecoder(toObjectMap().unwrapRoot(), customSerializers))
 
-@Suppress("UNNECESSARY_NOT_NULL_ASSERTION")
-fun DataSnapshot.toObjectMap(): Pair<String, Any> =
-    (key ?: "root") to (if (hasChildren()) children.associate { it.toObjectMap() } else value)!!
+fun DataSnapshot.toObjectMap(): Pair<String, Any> {
+    val key = key ?: "root"
+    val value = when {
+        hasChildren() -> children
+            .map(DataSnapshot::toObjectMap)
+            .ensureTypeIsFirst()
+            .toMap()
+
+        else -> value
+    }
+    return key to value!!
+}
 
 @Suppress("UNCHECKED_CAST")
 fun Pair<String, Any>.unwrapRoot() = second as Map<String, Any>
+
+internal fun <A : Comparable<A>, B> Iterable<Pair<A, B>>.ensureTypeIsFirst(): Iterable<Pair<A, B>> =
+    sortedWith { a, b ->
+        when {
+            a.first == "type" -> -1
+            b.first == "type" -> 1
+            else -> a.first.compareTo(b.first)
+        }
+    }