/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.brooklyn.util.core.task;

import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ExecutionException;

import org.apache.brooklyn.api.mgmt.Task;
import org.apache.brooklyn.util.exceptions.Exceptions;
import org.apache.brooklyn.util.text.Strings;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;

/**
 * Runs {@link Task}s in parallel.
 *
 * No guarantees of order of starting the tasks, but the return value is a
 * {@link List} of the return values of supplied tasks in the same
 * order they were passed as arguments.
 */
public class ParallelTask<T> extends CompoundTask<T> {
    public ParallelTask(Object... tasks) { super(tasks); }
    
    public ParallelTask(Map<String,?> flags, Collection<? extends Object> tasks) { super(flags, tasks); }
    public ParallelTask(Collection<? extends Object> tasks) { super(tasks); }
    
    public ParallelTask(Map<String,?> flags, Iterable<? extends Object> tasks) { super(flags, ImmutableList.copyOf(tasks)); }
    public ParallelTask(Iterable<? extends Object> tasks) { super(ImmutableList.copyOf(tasks)); }

    @Override
    protected List<T> runJobs() throws InterruptedException, ExecutionException {
        setBlockingDetails("Executing "+
                (children.size()==1 ? "1 child task" :
                children.size()+" children tasks in parallel") );
        for (Task<? extends T> task : children) {
            submitIfNecessary(task);
        }

        List<T> result = Lists.newArrayList();
        List<Exception> exceptions = Lists.newArrayList();
        for (Task<? extends T> task : children) {
            T x;
            try {
                x = task.get();
            } catch (Exception e) {
                Exceptions.propagateIfFatal(e);
                if (TaskTags.isInessential(task)) {
                    // ignore exception as it's inessential
                } else {
                    exceptions.add(e);
                }
                x = null;
            }
            result.add(x);
        }
        
        if (exceptions.isEmpty()) {
            return result;
        } else {
            if (result.size()==1 && exceptions.size()==1)
                throw Exceptions.propagate( exceptions.get(0) );
            throw Exceptions.propagate(exceptions.size()+" of "+result.size()+" parallel child task"+Strings.s(result.size())+" failed", exceptions);
        }
    }
}