import java.util.*;
import java.util.stream.Collectors;

public class StreamExample {

    private static class HW1Date {
        int day;
        int month;
        int year;

        HW1Date(int day, int month, int year) {
            this.day = day;
            this.month = month;
            this.year = year;
        }

        public String toString() {
            return "day: " + day + " month: " + month + " year: " + year;
        }
    }

    public static void main(String[] args) {

        /*
         * 4.
         *
         * Write a function dates_in_month that takes a list of dates and a month 
         * (i.e., an int) and returns a list holding the dates from the argument list 
         * of dates that are in the month. 
         *
         * The returned list should contain dates in the order they were originally given.
         *
         * Let's try this without using the stream API...
         */
        List<HW1Date> dates = Arrays.asList(new HW1Date[] {
            new HW1Date(1, 1, 1500), new HW1Date(2, 2, 1900),
            new HW1Date(10, 4, 3104), new HW1Date(20, 7, 2004)
        });

        // With no stream API
        for (HW1Date d : datesInMonthNoStream(dates, 2)) {
            System.out.println(d);
        }

        // With the stream API! Instead of using a for each loop, we can instead use the .forEach
        // function introduced in the Collection interface!
        datesInMonthStream(dates, 2).forEach(d -> System.out.println(d));

        // But hm... the above method looks a lot like function wrapping though. Instead, we can actually
        // use method references! 'System.out' is an object that has a 'println' method. Thus, we can actually just
        // say this instead:
        datesInMonthStream(dates, 2).forEach(System.out::println);
    }

    public static List<HW1Date> datesInMonthNoStream(List<HW1Date> dates, int month) {
        List<HW1Date> res = new ArrayList<>();

        for (HW1Date date : dates) {
            if (date.month == month) {
                res.add(date);
            }
        }

        return res;
    }

    // Neat, it's a single concise line! 
    public static List<HW1Date> datesInMonthStream(List<HW1Date> dates, int month) {
        return dates.stream().filter(d -> d.month == month).collect(Collectors.toList());
    }

}