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/*
 * 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.gh.bmd.jrt.channel;

import com.gh.bmd.jrt.channel.StandaloneChannel.StandaloneInput;
import com.gh.bmd.jrt.core.JRoutine;
import com.gh.bmd.jrt.invocation.StatelessInvocation;

import java.util.List;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;

/**
 * Utility class for handling channels.
 * 
 * Created by davide on 3/15/15.
 */
public class Channels {

    /**
     * Avoid direct instantiation.
     */
    protected Channels() {

    }

    /**
     * Merges the specified channels into a selectable one.
     * 

     * Note that the channels will be bound as a result of the call.
     *
     * @param channels the channels to merge.
     * @param  the output data type.
     * @return the selectable output channel.
     * @throws java.lang.IllegalArgumentException if the specified list is empty.
     * @throws java.lang.NullPointerException     if the specified list is null.
     */
    @Nonnull
    public static  OutputChannel> select(
            @Nonnull final List> channels) {

        if (channels.isEmpty()) {

            throw new IllegalArgumentException("the list of channels cannot be empty");
        }

        final StandaloneChannel> standalone =
                JRoutine.standalone().buildChannel();
        final StandaloneInput> input = standalone.input();
        int i = 0;

        for (final OutputChannel channel : channels) {

            input.pass(selectable(i++, channel));
        }

        input.close();
        return standalone.output();
    }

    /**
     * Returns a new channel making the specified one selectable.

     * Each output will be passed along unchanged.
     * 
     * Note that the channel will be bound as a result of the call.
     *
     * @param index    the channel index.
     * @param channel  the channel to make selectable.
     * @param  the output data type.
     * @return the selectable output channel.
     */
    @Nonnull
    public static  OutputChannel> selectable(final int index,
            @Nullable final OutputChannel channel) {

        return JRoutine.on(new StatelessInvocation>() {

            public void onInput(final OUTPUT output,
                    @Nonnull final ResultChannel> result) {

                result.pass(new Selectable(output, channel, index));
            }
        }).callSync(channel);
    }

    /**
     * Data class storing information about the origin of the data.
     *
     * @param  the data type.
     */
    @SuppressFBWarnings(value = "URF_UNREAD_PUBLIC_OR_PROTECTED_FIELD",
            justification = "this is an immutable data class")
    public static class Selectable {

        /**
         * The origin channel.
         */
        public final Channel channel;

        /**
         * The data object.
         */
        public final DATA data;

        /**
         * The origin channel index.
         */
        public final int index;

        /**
         * Constructor.
         *
         * @param data    the data object.
         * @param channel the origin channel.
         * @param index   the channel index.
         */
        public Selectable(final DATA data, final Channel channel, final int index) {

            this.data = data;
            this.channel = channel;
            this.index = index;
        }
    }
}