Generic Position serializer

geojson/src/commonMain/kotlin/org/maplibre/spatialk/geojson/serialization/PositionSerializer.kt

@@ -1,56 +1,45 @@
 package org.maplibre.spatialk.geojson.serialization
 
+import kotlinx.serialization.ExperimentalSerializationApi
 import org.maplibre.spatialk.geojson.Position
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.SerializationException
+import kotlinx.serialization.builtins.ListSerializer
+import kotlinx.serialization.builtins.serializer
 import kotlinx.serialization.descriptors.SerialDescriptor
-import kotlinx.serialization.descriptors.StructureKind
-import kotlinx.serialization.descriptors.buildSerialDescriptor
+import kotlinx.serialization.descriptors.listSerialDescriptor
 import kotlinx.serialization.encoding.Decoder
 import kotlinx.serialization.encoding.Encoder
-import kotlinx.serialization.json.JsonDecoder
-import kotlinx.serialization.json.JsonEncoder
-import kotlinx.serialization.json.add
-import kotlinx.serialization.json.buildJsonArray
-import kotlinx.serialization.json.double
-import kotlinx.serialization.json.jsonArray
-import kotlinx.serialization.json.jsonPrimitive
 
 /**
  * [KSerializer] implementation for implementations of the [Position] interface.
  * Serializes a Position down to an array of numbers as specified by GeoJSON.
- * This serializer only works for converting to and from JSON.
  * A position maps to `[longitude, latitude, altitude]`.
  *
  * A position's [altitude][Position.altitude] is only included in the array if it is not null.
  */
 public object PositionSerializer : KSerializer<Position> {
-    override val descriptor: SerialDescriptor
-        get() = buildSerialDescriptor("Position", StructureKind.LIST)
+    @OptIn(ExperimentalSerializationApi::class)
+    override val descriptor: SerialDescriptor =
+        listSerialDescriptor(Double.serializer().descriptor)
 
     override fun deserialize(decoder: Decoder): Position {
-        val input = decoder as? JsonDecoder ?: throw SerializationException("This class can only be loaded from JSON")
+        val list = ListSerializer(Double.serializer()).deserialize(decoder)
 
-        val array = input.decodeJsonElement().jsonArray
+        if (list.size < 2) {
+            throw SerializationException("Position data requires at least 2 doubles (longitude, latitude). Found: ${list.size}")
+        }
 
-        return Position(
-            array[0].jsonPrimitive.double,
-            array[1].jsonPrimitive.double,
-            array.getOrNull(2)?.jsonPrimitive?.double
-        )
+        return Position(list[0], list[1], if (list.size > 2) list[2] else null)
     }
 
     override fun serialize(encoder: Encoder, value: Position) {
-        encoder as? JsonEncoder ?: throw SerializationException("This class can only be saved as JSON")
-
-        val array = buildJsonArray {
-            add(value.longitude)
-            add(value.latitude)
-            if (value.altitude != null) {
-                add(value.altitude)
-            }
-        }
-
-        encoder.encodeJsonElement(array)
+        ListSerializer(Double.serializer()).serialize(
+            encoder, mutableListOf(
+                value.longitude,
+                value.latitude
+            ).let { list ->
+                value.altitude?.let { list.plus(it) } ?: list
+            })
     }
 }