package edd.util;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

public class ListsAndIterators {

    public static <T> List<T> duplicate(List<T> list) {
        List<T> result = new ArrayList<>();
        for (T elem : list) {
            result.add(elem);
            result.add(elem);
        }
        return result;
    }

    public static <T> List<T> consecute(List<T> list) {
        List<T> result = new ArrayList<>();
        int c = 1;
        for (T elem : list) {
            for (int i = 0; i < c; i++) {
                result.add(elem);
            }
            c++;
        }
        return result;
    }
    
    public static <T> List<T> removeDuplicates(List<T> list) {
        List<T> result = new ArrayList<>();        
        for (T elem : list) {
            if (!result.contains(elem)) {
                result.add(elem);
            }
        }
        return result;
    }

    private static class Pow2Iterator implements Iterator<Integer> {

        private int n;
        private int i;
        private int result;

        public Pow2Iterator(int n) {
            this.n = n;
            this.i = 0;
            this.result = 1;
        }

        @Override
        public boolean hasNext() {
            return i < n;
        }

        @Override
        public Integer next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            int r = result;
            result *= 2;
            i++;
            return r;
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    public static Iterator<Integer> pow2(int n) {
        return new Pow2Iterator(n);
    }

    private static class PrimesIterator implements Iterator<Integer> {

        private int current;
        private int max;

        public PrimesIterator(int max) {
            this.max = max;
            this.current = 2;
        }

        @Override
        public boolean hasNext() {
            return current <= max;
        }

        private boolean isPrime(int n) {
            for (int i = 2; i < n; i++) {
                if (n % i == 0) {
                    return false;
                }
            }
            return true;
        }

        private void getNextPrime() {
            while (!isPrime(++current))
                ;
        }

        @Override
        public Integer next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }

            int result = current;
            getNextPrime();
            return result;
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    public static Iterator<Integer> primes(int max) {
        return new PrimesIterator(max);
    }
    
    private static class SquaresIterator implements Iterator<Integer> {
        
        private int[] array;
        private int currentIndex;
        
        public SquaresIterator(int[] list) {
            this.array = list;
            this.currentIndex = 0;
        }

        @Override
        public boolean hasNext() {            
            return currentIndex < array.length;
        }

        @Override
        public Integer next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            
            int x = array[currentIndex];
            currentIndex++;
            return x * x;
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();            
        }               
    }
    
    public static Iterator<Integer> squares(int[] array) {
        return new SquaresIterator(array);
    }

}