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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.Order;
import java.util.Map;
import java.util.function.Predicate;
import static java.util.stream.Collectors.*;

/**
 * A demo shows how does Stream's aggregation works. Demo shows 1. Sum operation
 * on stream interface 2. Use Stream's count operation as Function output
 *
 * @author tyan
 */
public class Aggregation extends DemoHelper {

    /**
     * Calculate total product's price.
     *
     * @return total product's price
     */
    public static double totalProductPrice() {
        return products.stream().
                //map every product to its price
                mapToDouble(p -> p.getUnitPrice() * p.getUnitsInStock()).
                //caculation total price
                sum();
    }

    /**
     * Get every customer's order count that order meets the predicate<p>
     * It's possible some customers who don't have any order in given period.
     *
     * @param predicate a order predicate
     * @return map for customer's name and its number of order meets the predicate.
     */
    public static Map<String, Long> customerAndOrderCount(
            Predicate<Order> predicate) {
        return customers.stream().
                //convert customers into a map that key is customer's name and
                //value is number of orders which filter by predicate
                collect(toMap(
                        Customer::getCompanyName, c
                        -> c.getOrders().stream().
                        //filter orders' stream by given predicate
                        filter(predicate).
                        //get number of order which filter by given predicate
                        count()
                ));
    }
}