/*
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 *
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 *     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
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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.Vendor;
import stream.data.Product;
import java.util.Map;
import java.util.Optional;
import java.util.function.BinaryOperator;
import static java.util.stream.Collectors.*;
import java.util.stream.Stream;

/**
 * This class demos find operation that attach to collection, findFirst returns
 * first element in the stream, it's reasonable we can expect it's the first
 * element in the collection if collection is ordered. On the contrary, findAny
 * returns any element in the stream.
 *
 * @author tyan
 */
public class Elements extends DemoHelper {

    /**
     * Find any vendor or first vendor in country, this demos how implement a
     * simple find on a source with one condition
     *
     * @param findAny true perform findAny on stream false perform findFirst on
     * stream
     * @param country vendor's country
     * @return any/first vendor in given country
     */

    public static Optional<Vendor> vendorsInCountry(boolean findAny,
            String country) {
        Stream<Vendor> s = vendors.stream().
                //filter vendor who is same sa given country
                filter(vendor -> country.
                        equals(vendor.getCountry()));

        return findAny ? s.findAny() : s.findFirst();
    }

    /**
     * Get mapping table between category to any/first in-stock product.
     *
     * @param findAny true perform findAny on stream false perform findFirst on
     * stream
     * @return a map mapping every category to any/first in-stock product
     */
    public static Map<String, Product> inStockProductsByCategory(
            boolean findAny) {
        //A BinaryOperator only select first non-null element
        BinaryOperator<Product> reduceToFirstMatch = (l, r) -> (l != null)
                ? l : (r != null && r.getUnitsInStock() > 0)
                ? r : null;

        //grouping products by category, pick first element in same category
        return products.stream().collect(
                groupingBy(Product::getCategory,
                        reducing(null, reduceToFirstMatch)));
    }
}