/*
 * Copyright DataStax, Inc.
 *
 * 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 com.datastax.oss.driver.internal.core.util.concurrent;

import com.datastax.oss.driver.api.core.DriverException;
import com.datastax.oss.driver.api.core.DriverExecutionException;
import com.datastax.oss.driver.shaded.guava.common.base.Preconditions;
import com.datastax.oss.driver.shaded.guava.common.base.Throwables;
import java.util.List;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Supplier;

public class CompletableFutures {

  public static <T> CompletableFuture<T> failedFuture(Throwable cause) {
    CompletableFuture<T> future = new CompletableFuture<>();
    future.completeExceptionally(cause);
    return future;
  }

  /** Completes {@code target} with the outcome of {@code source}. */
  public static <T> void completeFrom(CompletionStage<T> source, CompletableFuture<T> target) {
    source.whenComplete(
        (t, error) -> {
          if (error != null) {
            target.completeExceptionally(error);
          } else {
            target.complete(t);
          }
        });
  }

  /** @return a completion stage that completes when all inputs are done (success or failure). */
  public static <T> CompletionStage<Void> allDone(List<CompletionStage<T>> inputs) {
    CompletableFuture<Void> result = new CompletableFuture<>();
    if (inputs.isEmpty()) {
      result.complete(null);
    } else {
      final int todo = inputs.size();
      final AtomicInteger done = new AtomicInteger();
      for (CompletionStage<?> input : inputs) {
        input.whenComplete(
            (v, error) -> {
              if (done.incrementAndGet() == todo) {
                result.complete(null);
              }
            });
      }
    }
    return result;
  }

  /** Do something when all inputs are done (success or failure). */
  public static <T> void whenAllDone(
      List<CompletionStage<T>> inputs, Runnable callback, Executor executor) {
    allDone(inputs).thenRunAsync(callback, executor).exceptionally(UncaughtExceptions::log);
  }
  /**
   * @return a completion stage that completes when all inputs are successful, or fails if any of
   *     them failed.
   */
  public static <T> CompletionStage<Void> allSuccessful(List<CompletionStage<T>> inputs) {
    CompletableFuture<Void> result = new CompletableFuture<>();
    if (inputs.isEmpty()) {
      result.complete(null);
    } else {
      final int todo = inputs.size();
      final AtomicInteger done = new AtomicInteger();
      final CopyOnWriteArrayList<Throwable> errors = new CopyOnWriteArrayList<>();
      for (CompletionStage<?> input : inputs) {
        input.whenComplete(
            (v, error) -> {
              if (error != null) {
                errors.add(error);
              }
              if (done.incrementAndGet() == todo) {
                if (errors.isEmpty()) {
                  result.complete(null);
                } else {
                  Throwable finalError = errors.get(0);
                  for (int i = 1; i < errors.size(); i++) {
                    finalError.addSuppressed(errors.get(i));
                  }
                  result.completeExceptionally(finalError);
                }
              }
            });
      }
    }
    return result;
  }

  /** Get the result now, when we know for sure that the future is complete. */
  public static <T> T getCompleted(CompletionStage<T> stage) {
    CompletableFuture<T> future = stage.toCompletableFuture();
    Preconditions.checkArgument(future.isDone() && !future.isCompletedExceptionally());
    try {
      return future.get();
    } catch (InterruptedException | ExecutionException e) {
      // Neither can happen given the precondition
      throw new AssertionError("Unexpected error", e);
    }
  }

  /** Get the error now, when we know for sure that the future is failed. */
  public static Throwable getFailed(CompletionStage<?> stage) {
    CompletableFuture<?> future = stage.toCompletableFuture();
    Preconditions.checkArgument(future.isCompletedExceptionally());
    try {
      future.get();
      throw new AssertionError("future should be failed");
    } catch (InterruptedException e) {
      throw new AssertionError("Unexpected error", e);
    } catch (ExecutionException e) {
      return e.getCause();
    }
  }

  public static <T> T getUninterruptibly(CompletionStage<T> stage) {
    boolean interrupted = false;
    try {
      while (true) {
        try {
          return stage.toCompletableFuture().get();
        } catch (InterruptedException e) {
          interrupted = true;
        } catch (ExecutionException e) {
          Throwable cause = e.getCause();
          if (cause instanceof DriverException) {
            throw ((DriverException) cause).copy();
          }
          Throwables.throwIfUnchecked(cause);
          throw new DriverExecutionException(cause);
        }
      }
    } finally {
      if (interrupted) {
        Thread.currentThread().interrupt();
      }
    }
  }

  /**
   * Executes a function on the calling thread and returns result in a {@link CompletableFuture}.
   *
   * <p>Similar to {@link CompletableFuture#completedFuture} except takes a {@link Supplier} and if
   * the supplier throws an unchecked exception, the returning future fails with that exception.
   *
   * @param supplier Function to execute
   * @param <T> Type of result
   * @return result of function wrapped in future
   */
  public static <T> CompletableFuture<T> wrap(Supplier<T> supplier) {
    try {
      return CompletableFuture.completedFuture(supplier.get());
    } catch (Throwable t) {
      return failedFuture(t);
    }
  }

  public static void whenCancelled(CompletionStage<?> stage, Runnable action) {
    stage.exceptionally(
        (error) -> {
          if (error instanceof CancellationException) {
            action.run();
          }
          return null;
        });
  }

  public static void propagateCancellation(CompletionStage<?> source, CompletionStage<?> target) {
    whenCancelled(source, () -> target.toCompletableFuture().cancel(true));
  }
}
