package java8.streams;

import java.util.Arrays;
import java.util.List;


public class ReduceTest {
	static class Person implements Comparable<Person> {
	    String name;
	    int age;

	    Person(String name, int age) {
	        this.name = name;
	        this.age = age;
	    }

	    @Override
	    public String toString() {
	        return name;
	    }

		@Override
		public int compareTo(Person other) {
			if(this.age == other.age) return 0;
			else return ((this.age > other.age) ?  1 :  -1);
		}
	}
	public static void main(String[] args) {
		List<Person> persons =
			    Arrays.asList(
			        new Person("Max", 18),
			        new Person("Peter", 23),
			        new Person("Pamela", 23),
			        new Person("David", 12));

		// Reduces a stream of elements to exactly one element of the stream
		persons
	    .stream()
	    .reduce((p1, p2) -> p1.age > p2.age ? p1 : p2)
	    .ifPresent(System.out::println);    // Pamela

		// method accepts both an identity value and a BinaryOperator accumulator. This method can be utilized to construct a new
		Person result =
			    persons
			        .stream()
			        .reduce(new Person("",0), (p1, p2) -> {
			        	p1.age += p2.age;
			        	p1.name += p2.name;
			        	return p1;
			        });

			System.out.format("name=%s; age=%s", result.name, result.age);
			System.out.println();
			System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
			// The third reduce method accepts three parameters: an identity value, a BiFunction accumulator and a combiner function of type BinaryOperator
			Integer ageSum = persons
				    .stream()
				    .reduce(0, (sum, p) -> sum += p.age, (sum1, sum2) -> sum1 + sum2);

				System.out.println(ageSum);  // 76
				System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
			//Third reduce in details
				Integer ageSumDtails = persons
					    .stream()
					    .reduce(0,
					    (sum, p) -> {
					    	System.out.format("accumulator: sum=%s; person=%s\n", sum, p);
					    	return  sum + p.age;
					    },
					    (sum1, sum2) -> {
					    	 System.out.format("combiner: sum1=%s; sum2=%s\n", sum1, sum2);
					    	return sum1 + sum2;
					    });
				System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
		// Combiner getting called in .parallelStream()

				//Third reduce in details
				Integer ageSumParallel = persons
					    .parallelStream()
					    .reduce(0,
					    (sum, p) -> {
					    	System.out.format("accumulator: sum=%s; person=%s\n", sum, p);
					    	return  sum + p.age;
					    },
					    (sum1, sum2) -> {
					    	 System.out.format("combiner: sum1=%s; sum2=%s\n", sum1, sum2);
					    	return sum1 + sum2;
					    });
	}

}