package il.ac.tau.cs.franji;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.stream.StreamSupport;

/**
 * Printing N first primary numbers - several ways to do it in Java
 * https://pastebin.com/tQdxerxD
 */
public class Primes {
    public static void printNPrimesArray(int N) {
        int[] primes = new int[N];
        int nextIndex = 0;
        int k = 1;  //starts with 2 as there is a += at loop start
        while (nextIndex < N) {
            k += 1;
            // check if k prime
            boolean isPrime = true;
            for (int i = 0; i < nextIndex; i++) {
                int p = primes[i];
                if ((k % p) == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime) {
                primes[nextIndex++] = k;
            }
        }
        // now print the primes
        for (int p : primes) {
            System.out.println(p);
        }
    }

    public static void printNPrimesArrayList(int N) {
        ArrayList<Integer> primes = new ArrayList<>();
        int k = 1;  //starts with 2 as there is a += at loop start
        while (primes.size() < N) {
            k += 1;
            // check if k prime
            boolean isPrime = true;
            for (int p : primes) {
                if ((k % p) == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime) {
                primes.add(k);
            }
        }
        // now print the primes
        for (int p : primes) {
            System.out.println(p);
        }
    }

    public static void printNPrimesStreams(int N) {
        ArrayList<Integer> primes = new ArrayList<>();
        int k = 1;  //starts with 2 as there is a += at loop start
        while (primes.size() < N) {
            k += 1;
            // check if k prime
            final int kk = k;
            if (primes.stream().allMatch(p -> (kk % p) != 0)) {
                primes.add(k);
            }
        }
        // now print the primes
        for (int p : primes) {
            System.out.println(p);
        }
    }

    static class PrimesIteratable implements Iterable<Integer> {
        ArrayList<Integer> primes = new ArrayList<>();

        class PrimesIterator implements Iterator<Integer> {
            int k = 1;

            @Override
            public boolean hasNext() {
                return true;  // primes is infinite
            }

            @Override
            public Integer next() {
                for (; ; ) {
                    this.k++;
                    boolean isPrime = true;
                    boolean addToPrimes = true;
                    for (int p : primes) {
                        if (p >= k) {
                            // the primes array may have more values since it was built by another iterator
                            addToPrimes = false;
                            isPrime = p == k;
                            break;
                        }
                        if ((k % p) == 0) {
                            isPrime = false;
                            break;
                        }
                    }
                    if (isPrime) {
                        if (addToPrimes) {
                            // note - adding to parent class array - shared by all iterators
                            primes.add(k);
                        }
                        return k;
                    }
                }
            }
        }

        @Override
        public Iterator<Integer> iterator() {
            return new PrimesIterator();
        }
    }


    public static void main(String[] args) {
        System.out.println("--- printNPrimesArray(20) ---");
        printNPrimesArray(20);
        System.out.println("--- printNPrimesArrayList(20) ---");
        printNPrimesArrayList(20);
        System.out.println("--- printNPrimesStreams(20) ---");
        printNPrimesStreams(20);

        System.out.println("--- PrimesIteratable -take 1 (30) ---");
        // primesIter is an infinite list of primes you can iterate over.
        PrimesIteratable primesIter = new PrimesIteratable();
        int i = 0;
        for (int p : primesIter) {
            System.out.println(p);
            if (i++ >= 30) {
                break;
            }
        }
        System.out.println("--- PrimesIteratable -take 2 (20) ---");
        // Using the same iterable again - primes array inside it is already initialized
        i = 0;
        for (int p : primesIter) {
            System.out.println(p);
            if (i++ >= 20) {
                break;
            }
        }
        System.out.println("--- PrimesIteratable -convert to stream limit(20) ---");
        StreamSupport.stream(primesIter.spliterator(), false).limit(20).forEach(p -> System.out.println(p));
    }
}