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/*
 * Copyright 2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ratpack.exec.internal;

import ratpack.exec.*;
import ratpack.func.Action;
import ratpack.func.Function;
import ratpack.util.Exceptions;
import ratpack.util.internal.InternalRatpackError;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicReference;

public class DefaultPromise implements Promise {

  private final Upstream upstream;

  public DefaultPromise(Upstream upstream) {
    this.upstream = upstream;
  }

  @Override
  public void then(final Action then) {
    ThreadBinding.requireComputeThread("Promise.then() can only be called on a compute thread (use Promise.block() to use a promise on a blocking thread)");
    try {
      upstream.connect(new Downstream() {
        @Override
        public void success(T value) {
          try {
            then.execute(value);
          } catch (Throwable e) {
            throwError(e);
          }
        }

        @Override
        public void error(Throwable throwable) {
          throwError(throwable);
        }

        @Override
        public void complete() {}
      });
    } catch (ExecutionException e) {
      throw e;
    } catch (Exception e) {
      throw new InternalRatpackError("failed to add promise resume action", e);
    }
  }

  private void throwError(Throwable throwable) {
    ExecutionBacking.require().streamSubscribe(h ->
        h.complete(() -> {
          throw Exceptions.toException(throwable);
        })
    );
  }

  @Override
  public  Promise transform(Function, ? extends Upstream> upstreamTransformer) {
    try {
      return new DefaultPromise<>(upstreamTransformer.apply(upstream));
    } catch (Exception e) {
      throw Exceptions.uncheck(e);
    }
  }

  @Override
  public T block() throws Exception {
    ThreadBinding.requireBlockingThread("Promise.block() can only be used while blocking (i.e. use Promise.blocking() first)");
    ExecutionBacking backing = ExecutionBacking.require();
    CountDownLatch latch = new CountDownLatch(1);
    AtomicReference> resultReference = new AtomicReference<>();
    backing.streamSubscribe(handle ->
        upstream.connect(
          new Downstream() {
            @Override
            public void success(T value) {
              unlatch(Result.success(value));
            }

            @Override
            public void error(Throwable throwable) {
              unlatch(Result.error(throwable));
            }

            @Override
            public void complete() {
              unlatch(Result.success(null));
            }

            private void unlatch(Result result) {
              resultReference.set(result);
              handle.complete();
              latch.countDown();
            }
          }
        )
    );
    backing.eventLoopDrain();
    latch.await();
    return resultReference.get().getValueOrThrow();
  }

}