kotlin_repository_cache3.kt

class UserRepository4(
    original: UserDao
) {
  private val withCache = cache(original::getUser)
  private val withCache2 = cache(original::getUser2)

  fun getUser(id: Int, name: String): Single<User> = withCache(id, name)
}

interface UserDao {
  fun getUser(id: Int, name: String): Single<User> {
    return Single.just(User(id, name))
        .delay(500, TimeUnit.MILLISECONDS)
  }

  fun getUser2(id: Int, name: String, password: String): Single<User> {
    if (password.isEmpty()) return Single.error(Exception())
    return Single.just(User(id, name))
        .delay(500, TimeUnit.MILLISECONDS)
  }
}


fun <V1, V2, R> cache(invoker: Function2<V1, V2, Single<R>>): Function2<V1, V2, Single<R>> {
  return CacheDecorator2(invoker)
}

fun <V1, V2, V3, R> cache(invoker: Function3<V1, V2, V3, Single<R>>): Function3<V1, V2, V3, Single<R>> {
  return CacheDecorator3(invoker)
}

private typealias Function2CacheKey<A, B> = Pair<A, B>

private class CacheDecorator2<in V1, in V2, R>(
    private val invoker: Function2<V1, V2, Single<R>>
) : Function2<V1, V2, Single<R>> {
  private val cache = HashMap<Function2CacheKey<V1, V2>, R>()

  override fun invoke(p1: V1, p2: V2): Single<R> {
    val key = Function2CacheKey(p1, p2)
    cache[key]?.let { return Single.just(it) }
    return invoker(p1, p2).doOnSuccess { cache[key] = it }
  }
}


private typealias Function3CacheKey<A, B, C> = Triple<A, B, C>

private class CacheDecorator3<in V1, in V2, in V3, R>(
    private val invoker: Function3<V1, V2, V3, Single<R>>
) : Function3<V1, V2, V3, Single<R>> {
  private val cache = HashMap<Function3CacheKey<V1, V2, V3>, R>()

  override fun invoke(p1: V1, p2: V2, p3: V3): Single<R> {
    val key = Function3CacheKey(p1, p2, p3)
    cache[key]?.let { return Single.just(it) }
    return invoker(p1, p2, p3).doOnSuccess { cache[key] = it }
  }
}