Initial commit

futur-reactive-streams/src/main/java/dev/tommyjs/futur/reactivestreams/ReactiveTransformer.java

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+package dev.tommyjs.futur.reactivestreams;
+
+import dev.tommyjs.futur.promise.Promise;
+import org.jetbrains.annotations.NotNull;
+import org.reactivestreams.Publisher;
+
+public class ReactiveTransformer {
+
+    public static <T> @NotNull Promise<T> wrapPublisher(@NotNull Publisher<T> publisher) {
+        SingleAccumulatorSubscriber<T> subscriber = SingleAccumulatorSubscriber.create();
+        publisher.subscribe(subscriber);
+        return subscriber.getPromise();
+    }
+
+}

futur-reactive-streams/src/main/java/dev/tommyjs/futur/reactivestreams/SingleAccumulatorSubscriber.java

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+package dev.tommyjs.futur.reactivestreams;
+
+import dev.tommyjs.futur.promise.Promise;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
+
+public class SingleAccumulatorSubscriber<T> implements Subscriber<T> {
+
+    private final Promise<T> promise;
+
+    public SingleAccumulatorSubscriber(Promise<T> promise) {
+        this.promise = promise;
+    }
+
+    @Override
+    public void onSubscribe(Subscription s) {
+        s.request(1);
+    }
+
+    @Override
+    public void onNext(T t) {
+        promise.complete(t);
+    }
+
+    @Override
+    public void onError(Throwable t) {
+        promise.completeExceptionally(t);
+    }
+
+    @Override
+    public void onComplete() {
+        // ignore
+    }
+
+    public Promise<T> getPromise() {
+        return promise;
+    }
+
+    public static <T> SingleAccumulatorSubscriber<T> create(Promise<T> promise) {
+        return new SingleAccumulatorSubscriber<>(promise);
+    }
+
+    public static <T> SingleAccumulatorSubscriber<T> create() {
+        return create(new Promise<>());
+    }
+
+}