import java.lang.reflect.*

abstract class AbstractRepository<T>

@Suppress("UNCHECKED_CAST")
fun <T> Class<out AbstractRepository<T>>.repositoryType(): Class<T> =
    generateSequence<Type>(this) {
        (it as? Class<*> ?: (it as? ParameterizedType)?.rawType as? Class<*>)
            ?.genericSuperclass
    }
        .filterIsInstance<ParameterizedType>()
        .first { it.rawType == AbstractRepository::class.java }
        .actualTypeArguments
        .single() as Class<T>

class IntRepository : AbstractRepository<Int>()
class StringRepository : AbstractRepository<String>()
interface Foo
class FooRepository : AbstractRepository<Foo>()
class Bar
class BarRepository : AbstractRepository<Bar>()

fun main() {
    println(IntRepository::class.java.repositoryType())
    println(StringRepository::class.java.repositoryType())
    println(FooRepository::class.java.repositoryType())
    println(BarRepository::class.java.repositoryType())
}