Gson adapter to add kotlin optionals check to gson deserializer

GsonKotlinAdapterFactory

private val TAG: String = "GsonKotlinAdapter"
/**
 * GsonKotlinAdapterFactory inspired by https://github.com/sargunv/gson-kotlin
 */


internal class GsonKotlinAdapterFactory : TypeAdapterFactory {

    private val Class<*>.isKotlinClass: Boolean
        get() = declaredAnnotations.find { it.annotationClass.java.name == "kotlin.Metadata" } != null

    override fun <T : Any> create(gson: Gson, type: TypeToken<T>): TypeAdapter<T>? {
        if (!type.rawType.isKotlinClass)
            return null

        val kClass = (type.rawType as Class<*>).kotlin

        @Suppress("UNCHECKED_CAST")
        return Adapter(this, gson, type, kClass as KClass<T>)
    }

    class Adapter<T : Any>(
        factory: GsonKotlinAdapterFactory,
        gson: Gson,
        type: TypeToken<T>,
        private val kClass: KClass<T>
    ) : TypeAdapter<T>() {

        val delegate: TypeAdapter<T> = gson.getDelegateAdapter(factory, type)

        override fun write(out: JsonWriter, value: T) = delegate.write(out, value)

        override fun read(input: JsonReader): T = delegate.read(input).apply { doNullCheck(this) }

        private fun doNullCheck(value: T?) {
            kClass.declaredMemberProperties.forEach { prop ->
                prop.isAccessible = true
                if (!prop.returnType.isMarkedNullable && value?.let { prop(it) } == null) {
                    val messageError = "Field: '${prop.name}' in Class '${kClass.simpleName}' is" +
                        " not marked nullable but found null value"
                    Log.e(TAG, messageError)
                    throw JsonParseException(messageError)
                }
            }
        }
    }
}