import javafx.util.Pair;

import java.util.ArrayList;
import java.util.List;

public class LineSimplification {
    private static class Point extends Pair<Double, Double> {
        Point(Double key, Double value) {
            super(key, value);
        }

        @Override
        public String toString() {
            return String.format("(%f, %f)", getKey(), getValue());
        }
    }

    private static double perpendicularDistance(Point pt, Point lineStart, Point lineEnd) {
        double dx = lineEnd.getKey() - lineStart.getKey();
        double dy = lineEnd.getValue() - lineStart.getValue();

        // Normalize
        double mag = Math.hypot(dx, dy);
        if (mag > 0.0) {
            dx /= mag;
            dy /= mag;
        }
        double pvx = pt.getKey() - lineStart.getKey();
        double pvy = pt.getValue() - lineStart.getValue();

        // Get dot product (project pv onto normalized direction)
        double pvdot = dx * pvx + dy * pvy;

        // Scale line direction vector and subtract it from pv
        double ax = pvx - pvdot * dx;
        double ay = pvy - pvdot * dy;

        return Math.hypot(ax, ay);
    }

    private static void ramerDouglasPeucker(List<Point> pointList, double epsilon, List<Point> out) {
        if (pointList.size() < 2) throw new IllegalArgumentException("Not enough points to simplify");

        // Find the point with the maximum distance from line between the start and end
        double dmax = 0.0;
        int index = 0;
        int end = pointList.size() - 1;
        for (int i = 1; i < end; ++i) {
            double d = perpendicularDistance(pointList.get(i), pointList.get(0), pointList.get(end));
            if (d > dmax) {
                index = i;
                dmax = d;
            }
        }

        // If max distance is greater than epsilon, recursively simplify
        if (dmax > epsilon) {
            List<Point> recResults1 = new ArrayList<>();
            List<Point> recResults2 = new ArrayList<>();
            List<Point> firstLine = pointList.subList(0, index + 1);
            List<Point> lastLine = pointList.subList(index, pointList.size());
            ramerDouglasPeucker(firstLine, epsilon, recResults1);
            ramerDouglasPeucker(lastLine, epsilon, recResults2);

            // build the result list
            out.addAll(recResults1.subList(0, recResults1.size() - 1));
            out.addAll(recResults2);
            if (out.size() < 2) throw new RuntimeException("Problem assembling output");
        } else {
            // Just return start and end points
            out.clear();
            out.add(pointList.get(0));
            out.add(pointList.get(pointList.size() - 1));
        }
    }

    public static void main(String[] args) {
        List<Point> pointList = List.of(
                new Point(0.0, 0.0),
                new Point(1.0, 0.1),
                new Point(2.0, -0.1),
                new Point(3.0, 5.0),
                new Point(4.0, 6.0),
                new Point(5.0, 7.0),
                new Point(6.0, 8.1),
                new Point(7.0, 9.0),
                new Point(8.0, 9.0),
                new Point(9.0, 9.0)
        );
        List<Point> pointListOut = new ArrayList<>();
        ramerDouglasPeucker(pointList, 1.0, pointListOut);
        System.out.println("Points remaining after simplification:");
        pointListOut.forEach(System.out::println);
    }
}