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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.Comparator;
import java.util.List;
import java.util.stream.Collectors;

/**
 * A demo shows how does Stream's subset works. This demo provides two methods
 * which is using substream method on Stream to get subset of the elements. Note
 * we can use substream on sorted stream to get top number elements, but we
 * can't guarantee the element order if stream is not sorted.
 *
 * @author hyan
 */
public class Subset extends DemoHelper {

    /**
     * Returns a List that contains numbers order which customer is from state,
     * also execute action on every returned order element. The number must be a
     * non-negative digit.
     * <p>
     *
     * @param number integer how many orders are expected to be returned
     * @param state state that customer of order belong to
     * @return a list contains top number customers that sorted by comp
     */
    public static List<Order> firstNOrdersFromState(int number,
            String state) {
        return customers.stream().
                //only take customers from a particular state
                filter(c -> state.equals(c.getRegion())).
                //get orders of those customers
                flatMap(c -> c.getOrders().stream()).
                //get first number of orders
                limit(number).
                //collect to a list
                collect(Collectors.toList());
    }

    /**
     * Returns a List that contains numbers customer sorted by comp, also
     * execute action on every returned customer element. The number must be a
     * non-negative digit.
     * <p>
     *
     * @param number integer how many customers are expected to be returned
     * @param comp Comparator to compare customer
     * @return a list contains top number customers that sorted by comp
     */
    public static List<Customer> topNCustomer(int number,
            Comparator<Customer> comp) {
        //We keep result in topN, then we can test it
        return customers.stream()
.                //sort customers by comp
                sorted(comp).
                //get first number of orders
                limit(number).
                //collect to a list
                collect(Collectors.toList());
    }
}