core/src/main/java/org/apache/commons/functor/core/algorithm/FindWithinGenerator.java

/*
 * 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.commons.functor.core.algorithm;

import java.io.Serializable;
import java.util.NoSuchElementException;

import org.apache.commons.functor.BinaryFunction;
import org.apache.commons.functor.Predicate;
import org.apache.commons.functor.Procedure;
import org.apache.commons.functor.generator.Generator;

/**
 * Return the first Object in a {@link Generator} matching a {@link Predicate}.
 *
 * @param <E> the arguments type.
 * @version $Revision$ $Date$
 */
public final class FindWithinGenerator<E>
    implements BinaryFunction<Generator<? extends E>, Predicate<? super E>, E>, Serializable {

    /**
     * Basic instance.
     */
    public static final FindWithinGenerator<Object> INSTANCE = new FindWithinGenerator<Object>();

    /**
     * serialVersionUID declaration.
     */
    private static final long serialVersionUID = -2824239991638326134L;

    /**
     * Helper procedure.
     *
     * @param <T> the argument type.
     */
    private static class FindProcedure<T> implements Procedure<T> {
        /**
         * The object found, if any.
         */
        private T found;
        /**
         * Flag to mark an object has been found.
         */
        private boolean wasFound;
        /**
         * The adapted predicate.
         */
        private Predicate<? super T> pred;

        /**
         * Create a new FindProcedure.
         * @param pred the adapted predicate.
         */
        public FindProcedure(Predicate<? super T> pred) {
            this.pred = pred;
        }

        /**
         * {@inheritDoc}
         */
        public void run(T obj) {
            if (!wasFound && pred.test(obj)) {
                wasFound = true;
                found = obj;
            }
        }
    }

    /**
     * Flag to mark the {@link FindWithinGenerator#evaluate(Generator, Predicate)} method must return a user
     * defined object when the adapted procedure does not find any object.
     */
    private final boolean useIfNone;
    /**
     * Object to be returned in the case the adapted procedure does not find any object.
     */
    private final E ifNone;

    /**
     * Create a new FindWithinGenerator.
     */
    public FindWithinGenerator() {
        super();
        ifNone = null;
        useIfNone = false;
    }

    /**
     * Create a new FindWithinGenerator.
     * @param ifNone object to return if the Generator contains no matches.
     */
    public FindWithinGenerator(E ifNone) {
        super();
        this.ifNone = ifNone;
        useIfNone = true;
    }

    /**
     * {@inheritDoc}
     * @param left Generator
     * @param right Predicate
     */
    public E evaluate(Generator<? extends E> left, Predicate<? super E> right) {
        FindProcedure<E> findProcedure = new FindProcedure<E>(right);
        left.run(findProcedure);
        if (!findProcedure.wasFound) {
            if (useIfNone) {
                return ifNone;
            }
            throw new NoSuchElementException("No element matching " + right + " was found.");
        }
        return findProcedure.found;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof FindWithinGenerator<?>)) {
            return false;
        }
        FindWithinGenerator<?> other = (FindWithinGenerator<?>) obj;
        return other.useIfNone == useIfNone && !useIfNone
                || (other.ifNone == this.ifNone || other.ifNone != null && other.ifNone.equals(this.ifNone));
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public int hashCode() {
        if (!this.useIfNone) {
            return System.identityHashCode(INSTANCE);
        }
        int result = "FindWithinGenerator".hashCode();
        result ^= this.ifNone == null ? 0 : this.ifNone.hashCode();
        return result;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String toString() {
        return "FindWithinGenerator<" + ifNone + "," + useIfNone + ">";
    }

    /**
     * Get a static {@link FindWithinGenerator} instance.
     * @return {@link FindWithinGenerator}
     */
    public static FindWithinGenerator<Object> instance() {
        return INSTANCE;
    }
}