Extension function to convert Google Play Services Tasks result to RxJava Single

TasksRxExtensions.kt

import com.google.android.gms.tasks.Task
import io.reactivex.rxjava3.core.Single
import java.util.concurrent.CancellationException
import java.util.concurrent.TimeUnit

fun <T : Any> Task<T>.toSingle(): Single<T> {
  return if (isComplete) {
    Single.fromCallable(::asRequired)
  } else {
    Single.create<T> { emitter ->
      addOnCompleteListener {
        try {
          emitter.onSuccess(it.asRequired())
        } catch (e: Exception) {
          emitter.onError(e)
        }
      }
    }
  }
}

private fun <T : Any> Task<T>.asRequired(): T {
  return if (isComplete) {
    if (!isCanceled) {
      exception?.let { throw it } ?: result ?: throw IllegalStateException("Result of task $this was null")
    } else {
      throw CancellationException("Task $this was cancelled normally")
    }
  } else {
    throw IllegalStateException("Task $this not complete")
  }
}