package de.intevation.gnv.math;

import java.util.List;
import java.util.Collections;

import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.Envelope;

import com.vividsolutions.jts.index.quadtree.Quadtree;

/**
 *  @author Sascha L. Teichmann
 */
public final class Interpolation2D
{
    public interface Consumer {
        void interpolated(Coordinate point);
    } // interface Consumer

    private Interpolation2D() {
    }

    public static void interpolate(
        List<? extends Coordinate> path,
        List<? extends Point2d>    points,
        double                     from,
        double                     to,
        int                        steps,
        Metrics                    metrics,
        Consumer                   consumer
    ) {
        int N = path.size();
        int M = points.size();

        if (M < 1 || N < 2) { // nothing to do
            return;
        }
        // figure out max delta(p[i].x, p[i-1].x) 
        Collections.sort(points, Point2d.X_COMPARATOR);
        double dxMax = -Double.MAX_VALUE;
        for (int i = 1; i < M; ++i) {
            double dx = Math.abs(path.get(i).x - path.get(i-1).x);
            if (dx > dxMax) {
                dxMax = dx;
            }
        }

        dxMax = dxMax*0.5d + 1e-5d;

        // figure out max delta(p[i].y, p[i-1].y) 
        Collections.sort(path, Point2d.X_COMPARATOR);
        double dyMax = -Double.MAX_VALUE;
        for (int i = 1; i < M; ++i) {
            double dy = Math.abs(path.get(i).y - path.get(i-1).y);
            if (dy > dyMax) {
                dyMax = dy;
            }
        }

        dyMax = dyMax*0.5d + 1e-5d;

        // put into spatial index to speed up finding neighbors.
        Quadtree spatialIndex = new Quadtree();

        for (int i = 0; i < M; ++i) {
            Point2d p = points.get(i);
            spatialIndex.insert(p.envelope(), p);
        }

        LinearToMap linearToMap = new LinearToMap(
            path, from, to, metrics);

        double dP = (to - from)/steps;

        Coordinate center = new Coordinate();

        Envelope queryBuffer = new Envelope();

        Point2d [] neighbors = new Point2d[4];

        for (double p = to; p <= from; p += dP) {
            if (!linearToMap.locate(p, center)) {
                continue;
            }
            queryBuffer.init(
                center.x - dxMax, center.x + dxMax, 
                center.y - dyMax, center.y + dyMax);

            List potential = spatialIndex.query(queryBuffer);

            L1Comparator invL1 = new L1Comparator(center);
            Collections.sort(potential, invL1);

            neighbors[0] = neighbors[1] = 
            neighbors[2] = neighbors[3] = null;

            /* bit code of neighbors
               0---1
               | x |
               2---3
            */

            int mask = 0;
            // reversed order is essential here!
            for (int i = potential.size()-1; i >= 0; --i) {
                Point2d n = (Point2d)potential.get(i);
                int code = n.x > center.x ? 1 : 0;
                if (n.y > center.y) code |= 2;
                neighbors[code] = n;
                mask |= 1 << code;
            }

            int numNeighbors = Integer.bitCount(mask);

            // only interpolate if we have all four neighbors
            // and we do not have any gaps.
            if (numNeighbors == 4
            && !neighbors[0].hasIGap(neighbors[0])
            && !neighbors[1].hasJGap(neighbors[3])
            && !neighbors[3].hasIGap(neighbors[2])
            && !neighbors[2].hasJGap(neighbors[0])
            ) {
                double z1 = interpolate(
                    neighbors[0].x, neighbors[0].z,
                    neighbors[1].x, neighbors[1].z,
                    center.x);
                double z2 = interpolate(
                    neighbors[2].x, neighbors[2].z,
                    neighbors[3].x, neighbors[3].z,
                    center.x);
                double y1 = interpolate(
                    neighbors[0].x, neighbors[0].y,
                    neighbors[1].x, neighbors[1].y,
                    center.x);
                double y2 = interpolate(
                    neighbors[2].x, neighbors[2].y,
                    neighbors[3].x, neighbors[3].y,
                    center.x);
                center.z = interpolate(
                    y1, z1,
                    y2, z2,
                    center.y);
                consumer.interpolated(center);
            }
        }
    }

    public static final double interpolate(
        double x1, double y1,
        double x2, double y2,
        double x
    ) {
        if (x2 == x1) {
            return (y1 + y2)*0.5d;
        }
        double m = (y2-y1)/(x2-x1);
        double b = y1 - m*x1;
        return m*x + b;
    }
}
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