package com.company;

import com.sun.org.apache.xpath.internal.operations.Div;

import java.util.Random;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;

class DivideTask extends RecursiveTask<int[]> {

    int[] arrayToDivide;

    final private int TRESHHOLD =100;

    public DivideTask(int[] arrayToDivide) {
        this.arrayToDivide = arrayToDivide;
    }

    protected int[] compute() {

        if(arrayToDivide.length>1) {
            int[] array_left = new int[arrayToDivide.length / 2];
            int[] array_right = new int[arrayToDivide.length - array_left.length];

            System.arraycopy(arrayToDivide, 0, array_left, 0, array_left.length);
            System.arraycopy(arrayToDivide, array_left.length, array_right, 0, array_right.length);

            DivideTask task1 = new DivideTask(array_left);
            DivideTask task2 = new DivideTask(array_right);

            task1.fork();
            task2.fork();

            //Wait for results from both tasks
            int[] tab1 = task1.join();
            int[] tab2 = task2.join();
            int[] scal_tab = new int[tab1.length + tab2.length];

            scal_tab(tab1, tab2, scal_tab);

            return scal_tab;
        }
        return arrayToDivide;
    }

    private void scal_tab(
            int[] tab1,
            int[] tab2,
            int[] scal_tab) {

        int i = 0, j = 0, k = 0;

        while ((i < tab1.length) && (j < tab2.length)) {

            if (tab1[i] < tab2[j]) {
                scal_tab[k] = tab1[i++];
            } else {
                scal_tab[k] = tab2[j++];
            }

            k++;
        }

        if (i == tab1.length) {

            for (int a = j; a < tab2.length; a++) {
                scal_tab[k++] = tab2[a];
            }

        } else {

            for (int a = i; a < tab1.length; a++) {
                scal_tab[k++] = tab1[a];
            }

        }
    }

    public static void main(String[] args){
        int[] tab = randomTab();

        System.out.println("PRZED SORTOWANIEM:\n");
        printTab(tab);

        DivideTask task = new DivideTask(tab);
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        forkJoinPool.invoke(task);
        int[] tab2 = task.join();
        System.out.println("PO SORTOWANIU:\n");
        printTab(tab2);

    }

    public static int[] randomTab(){
        Random random = new Random();
        int[] tab = new int[20];
        for(int i =0;i<20;i++){
            tab[i] = random.nextInt(1000);
        }
        return tab;
    }

    public static void printTab(int[] tab){
        for(int i=0;i<tab.length;++i){
            System.out.print(tab[i]+" ");
        }
        System.out.println();
    }
}