org.jage.emas.util.ChainingContext.java Source code

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Here is the source code for org.jage.emas.util.ChainingContext.java

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/**
 * Copyright (C) 2006 - 2012
 *   Pawel Kedzior
 *   Tomasz Kmiecik
 *   Kamil Pietak
 *   Krzysztof Sikora
 *   Adam Wos
 *   Lukasz Faber
 *   Daniel Krzywicki
 *   and other students of AGH University of Science and Technology.
 *
 * This file is part of AgE.
 *
 * AgE is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * AgE is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with AgE.  If not, see <http://www.gnu.org/licenses/>.
 */
/*
 * Created: 2012-03-16
 * $Id: ChainingContext.java 471 2012-10-30 11:17:00Z faber $
 */

package org.jage.emas.util;

import java.util.List;

import org.jage.action.IActionContext;

import com.google.common.base.Optional;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Utility context which allow to chain ChainingAction subclasses. Contains a reference to the next action context in
 * the chain.
 *
 * @author AGH AgE Team
 */
public class ChainingContext implements IActionContext {

    private ChainingContext next;

    /**
     * Returns an optional next context.
     *
     * @return an optional next context
     */
    public final Optional<ChainingContext> getNextContext() {
        return Optional.fromNullable(next);
    }

    /**
     * Creates a new chaining context builder.
     *
     * @return an empty builder
     */
    public static ChainingContextBuilder builder() {
        return new ChainingContextBuilder();
    }

    /**
     * Helper builder class for {@link ChainingContext} chains.
     *
     * @author AGH AgE Team
     */
    public static final class ChainingContextBuilder {

        private ChainingContext first;

        private ChainingContext last;

        /**
         * Appends the given context to the chain. If the chain is empty, this context will be made the head of the
         * chain. This context next one will be set to null.
         *
         * @param next
         *            the next context
         * @return this builder
         */
        public ChainingContextBuilder append(final ChainingContext next) {
            checkNotNull(next);
            if (first == null) {
                first = next;
                last = next;
            } else {
                last.next = next;
                last = next;
            }
            last.next = null;
            return this;
        }

        /**
         * Appends all the given contexts to this chain.
         *
         * @param nexts
         *            a list of contexts
         * @return this builder
         */
        public ChainingContextBuilder appendAll(final List<ChainingContext> nexts) {
            for (ChainingContext next : nexts) {
                append(next);
            }
            return this;
        }

        /**
         * Appends the given context to this chain if the provided condition is true.
         *
         * @param condition
         *            some boolean condition
         * @param next
         *            the next context
         * @return this builder
         *
         * @see ChainingContextBuilder#append(ChainingContext)
         */
        public ChainingContextBuilder appendIf(final boolean condition, final ChainingContext next) {
            if (condition) {
                append(next);
            }
            return this;
        }

        /**
         * Appends all the given contexts to this chain, if the condition is true.
         *
         * @param condition
         *            some boolean condition
         * @param nexts
         *            a list of contexts
         * @return this builder
         * @see ChainingContextBuilder#appendAll(List)
         */
        public ChainingContextBuilder appendAllIf(final boolean condition, final List<ChainingContext> nexts) {
            if (condition) {
                appendAll(nexts);
            }
            return this;
        }

        /**
         * Check whether this chain is empty, i.e. whether it has no head element.
         *
         * @return true if the chain is empty
         */
        public boolean isEmpty() {
            return first == null;
        }

        /**
         * Returns the head context, if the chain is not empty.
         *
         * @return the chain head context
         * @throws NullPointerException
         *             if the chain is empty
         */
        public ChainingContext build() {
            return checkNotNull(first);
        }
    }
}