import java.util.ArrayList;

/**
 * A priority queue using an unordered arraylist at the back.  Hence, the equivalent of selection sort.
 * 
 * @param <K> the Key element. This must implement Comparable.
 * @param <V> The Value element.  This could be anything.
 * 
 * For methods that exactly follow the interface, see the documentation in the interface.
 * 
 * @author gtowell
 * Created APRIL 6, 2020
 * Modified: April 13, 2020
*/
public class PriorityQSelection<K extends Comparable<K>, V> extends AbstractPriorityQueue<K,V> {

    /** The thing actually holding the data in the priority queue.  Using an ArrayList
     * to get unbounded length.  
     */
    final private ArrayList<Entry<K,V>> pqStore;

    /**
     * Initialize the priority queue
     */
    public PriorityQSelection() {
        this(Ordering.MIN);
    }
    public PriorityQSelection(Ordering order) {
        this.order=order;
        pqStore = new ArrayList<>();
    }


    @Override
    public int size() {
        return pqStore.size();
    }

    @Override
    public boolean isEmpty() {
        return pqStore.isEmpty();
    }

    @Override
    public boolean offer(K newK, V newV) {
        Entry<K,V> entry = new Entry<>(newK, newV);
        pqStore.add(entry);
        // Note that this always succeeds, so always return true.
        return true;
    }

    /**
     * find and return the next item from the priority queue
     * @return the next item
     */
    private Entry<K,V> getNext() {
        if (isEmpty())
            return null;
        // if there are entries, then go through them all to find the next one.
        // must do this because entries are in no particular order.
        Entry<K,V> cmin = pqStore.get(0); // see with the item in position 0
        // the start doing comparisons with item in position 1.
        for (int i=1; i<pqStore.size(); i++) {
            Entry<K,V> curr = pqStore.get(i);
            int cmp = pqStore.get(i).doCompare(cmin);
            if (cmp<0) {
                cmin=curr;
            }
        }
        pqStore.remove(cmin);
        return cmin;
    }

    @Override
    public V poll() {
        Entry<K,V> entry = getNext();
        if (entry==null) return null;
        pqStore.remove(entry);
        return entry.theV;
    }

    @Override
    public V peek() {
        Entry<K,V> entry = getNext();
        if (entry==null) return null;
        return entry.theV;
    }

    public static void main(String[] args) {
        PriorityQSelection<Integer, String> pq = new PriorityQSelection<Integer, String>(Ordering.MIN);
        pq.offer(1,"Jane");
        pq.offer(10,"WET");
        pq.offer(5, "WAS");
        System.out.println(pq.poll());
        System.out.println(pq.poll());
        System.out.println(pq.poll());
        System.out.println();

        pq = new PriorityQSelection<>(Ordering.MAX);
        pq.offer(1,"Jane");
        pq.offer(10,"WET");
        pq.offer(5, "WAS");
        System.out.println(pq.poll());
        System.out.println(pq.poll());
        System.out.println(pq.poll());


    }

}