package mrhaki;

import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.function.Consumer;

class Async {

    private final ExecutorService executorService;
    private final WeatherService weatherService;

    Async(ExecutorService executorService, WeatherService weatherService) {
        this.executorService = executorService;
        this.weatherService = weatherService;
    }

    // Find temperature for a city using WeatherService and
    // assign result using callback argument.
    void findTemperature(String city, Consumer<Result> callback) {
        // Here we do an asynchronous call using ExecutorService and
        // a Runnable lambda.
        // We're assigning the result of calling WeatherService using
        // the callback argument.
        executorService.submit(() -> {
            int temperature = weatherService.getTemperature(city);
            var result = new Result(city, temperature);
            callback.accept(result);
        });
    }

    // Find temperature for multiple cities using WeatherService and
    // assign result using callback argument.
    void findTemperatures(List<String> cities, Consumer<Result> callback) {
        cities.forEach(city -> findTemperature(city, callback));
    }

    record Result(String city, int temperature) {
    }

    interface WeatherService {
        int getTemperature(String city);
    }
}

package mrhaki

import spock.lang.Specification
import spock.lang.Subject
import spock.util.concurrent.BlockingVariable
import spock.util.concurrent.BlockingVariables

import java.util.concurrent.Executors

class AsyncSpec extends Specification {

    // Provide a stub for the WeatherService interface.
    // Return 21 on the first call and 18 on subsequent calls.
    private Async.WeatherService weatherService = Stub() {
        getTemperature(_ as String) >>> [21, 18]
    }

    // We want to test the class Async
    @Subject
    private Async async = new Async(Executors.newFixedThreadPool(2), weatherService)

    void "findTemperature should return expected temperature"() {
        given:
        // We define a BlockingVariable to store the result in the callback,
        // so we can wait for the value in the then: block and
        // asssert the value when it becomes available.
        def result = new BlockingVariable<Async.Result>()

        when:
        // We invoke the async method and in the callback use
        // our BlockingVariable to set the result.
        async.findTemperature("Tilburg") { Async.Result temp ->
            // Set the result to the BlockingVariable.
            result.set(temp)
        }

        then:
        // Now we wait until the result is available with the
        // blocking call get().
        // Default waiting time is 1 second. We can change that
        // by providing the number of seconds as argument
        // to the BlockingVariable constructor.
        // E.g. new BlockingVariable<Long>(3) to wait for 3 seconds.
        result.get() == new Async.Result("Tilburg", 21)
    }

    void "findTemperatures should return expected temperatures"() {
        given:
        // With type BlockingVariables we can wait for multiple values.
        // Each value must be assigned to a unique key.
        def result = new BlockingVariables(5)

        when:
        async.findTemperatures(["Tilburg", "Amsterdam"]) { Async.Result temp ->
            // Set the result with a key to the BlockingVariables result variable.
            // We can story multiple results in one BlockingVariables.
            result[temp.city()] = temp.temperature()
        }

        then:
        // We wait for the results key by key.
        // We cannot rely that the result are available in the
        // same order as the passed input arguments Tilburg and Amsterdam
        // as the call will be asynchronous.
        // But using BlockingVariables we dont' have to care,
        // we simply request the value for a key and the code will
        // block until it is available.
        result["Amsterdam"] == 18
        result["Tilburg"] == 21
    }
}