package ags.utils.dataStructures.trees.thirdGenKD;

import ags.utils.dataStructures.BinaryHeap;
import ags.utils.dataStructures.IntervalHeap;
import ags.utils.dataStructures.MinHeap;

import java.util.Arrays;
import java.util.Iterator;

/**
 *
 */
public class NearestNeighborIterator<T> implements Iterator<T>, Iterable<T> {
    private DistanceFunction distanceFunction;
    private double[] searchPoint;
    private MinHeap<KdNode<T>> pendingPaths;
    private IntervalHeap<T> evaluatedPoints;
    private int pointsRemaining;
    private double lastDistanceReturned;

    protected NearestNeighborIterator(KdNode<T> treeRoot, double[] searchPoint, int maxPointsReturned, DistanceFunction distanceFunction) {
        this.searchPoint = Arrays.copyOf(searchPoint, searchPoint.length);
        this.pointsRemaining = Math.min(maxPointsReturned, treeRoot.size());
        this.distanceFunction = distanceFunction;
        this.pendingPaths = new BinaryHeap.Min<KdNode<T>>();
        this.pendingPaths.offer(0, treeRoot);
        this.evaluatedPoints = new IntervalHeap<T>();
    }

    /* -------- INTERFACE IMPLEMENTATION -------- */

    @Override
    public boolean hasNext() {
        return pointsRemaining > 0;
    }

    @Override
    public T next() {
        if (!hasNext()) {
            throw new IllegalStateException("NearestNeighborIterator has reached end!");
        }

        while (pendingPaths.size() > 0 && (evaluatedPoints.size() == 0 || (pendingPaths.getMinKey() < evaluatedPoints.getMinKey()))) {
            KdTree.nearestNeighborSearchStep(pendingPaths, evaluatedPoints, pointsRemaining, distanceFunction, searchPoint);
        }

        // Return the smallest distance point
        pointsRemaining--;
        lastDistanceReturned = evaluatedPoints.getMinKey();
        T value = evaluatedPoints.getMin();
        evaluatedPoints.removeMin();
        return value;
    }

    public double distance() {
        return lastDistanceReturned;
    }

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

    @Override
    public Iterator<T> iterator() {
        return this;
    }
}