/*
 * Copyright (c) 2013 Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 */

/*
 * This source code is provided to illustrate the usage of a given feature
 * or technique and has been deliberately simplified. Additional steps
 * required for a production-quality application, such as security checks,
 * input validation and proper error handling, might not be present in
 * this sample code.
 */
package stream;

import stream.data.Customer;
import stream.data.Product;
import java.util.Collection;
import java.util.Map;
import java.util.Optional;
import java.util.function.Function;
import static java.util.stream.Collectors.*;
import static java.util.Comparator.*;
import java.util.stream.Stream;

/**
 * This program is demo how to use the conversion operator like toArray,
 * collect(Collectors.toList()), collect(Collectors.toCollection())
 *
 * @author tyan
 */
public class Conversion extends DemoHelper {

    /**
     * Convert products which is most expensive in the same category into an
     * array
     *
     * @param func Function convert Product to T, T could be any type that
     * Product can convert, like price
     * @return product array which is in every category, value of T is highest
     */

    public static <T extends Comparable<T>> Product[] mostTProductsByCategory(
            Function<Product, T> func) {
        //Grouping product by category, only select maximal product by comparing
        //on func
        Map<String, Optional<Product>> categoryToProduct = products.stream().
                collect(groupingBy(Product::getCategory,
                                maxBy(comparing(func))));

        return categoryToProduct.values().stream().
                //get Product object
                map(Optional::get).
                //converting stream to an array
                toArray(Product[]::new);
    }

    /**
     * Convert customers to a distinct countries list
     *
     * @param ordered true keep original countries list order false not keep
     * original countries list order
     * @return a distinct ordered/unordered countries list for all of customers
     * by given ordered flag
     */
    public static Collection<String> countries(boolean ordered) {
        Stream<String> countries = customers.stream().map(Customer::getCountry);
        if (ordered) {
            /**
             * Use distinct() follow with collect(Collectors.toCollection) to
             * get unique countries linked list. Note this way can generate
             * target container
             */
            return countries.distinct().collect(toList());
        } else {
            /**
             * Use collect(Collectors.toSet) to get unique countries list. Note
             * the difference between this and first one is this way doesn't
             * guarantee the order
             */
            return countries.collect(toSet());
        }
    }
}