A serializer for kotlinx.serialization and KMongo that can accept either an int32 or a double and returns a double.

LenientDoubleArraySerializer.kt

/**
 * A serializer for kotlinx.serialization and KMongo that can accept either an int32 or a double and returns a double.
 * Depends on KMongo or another MongoDB library that uses [kbson](https://github.com/jershell/kbson), because 
 * its FlexibleDecoder gives a hint of what the type is before the value is decoded.
 * @author FluxCapacitor2
 */
object LenientDoubleArraySerializer : KSerializer<Array<Double>> {

    val s = ListSerializer(LenientDoubleSerializer)

    override val descriptor: SerialDescriptor
        get() = SerialDescriptor("custom.DoubleArray", s.descriptor)

    override fun deserialize(decoder: Decoder): Array<Double> {
        return s.deserialize(decoder).toTypedArray()
    }

    override fun serialize(encoder: Encoder, value: Array<Double>) {
        s.serialize(encoder, value.toList())
    }
}

object LenientDoubleSerializer : KSerializer<Double> {
    override val descriptor: SerialDescriptor
        get() = PrimitiveSerialDescriptor("custom.Double", PrimitiveKind.DOUBLE)

    override fun deserialize(decoder: Decoder): Double {
        decoder as FlexibleDecoder
        return when(decoder.reader.currentBsonType) {
            BsonType.INT32 -> decoder.reader.readInt32().toDouble()
            BsonType.DOUBLE -> decoder.reader.readDouble()
            else -> throw SerializationException("Invalid BSON type: ${decoder.reader.currentBsonType}")
        }
    }

    override fun serialize(encoder: Encoder, value: Double) {
        encoder.encodeDouble(value)
    }
}