package de.intevation.flys.geom.Lines;

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

import java.awt.geom.Point2D;
import java.awt.geom.Line2D;

import de.intevation.flys.artifacts.math.Linear;

public class Lines
{
    public static final double EPSILON = 1e-4;

    public static enum Mode { UNDEF, WET, DRY };

    protected Lines() {
    }

    public static final class StableIndex
    implements                Comparable<StableIndex>
    {
        protected Point2D point;
        protected int     index;

        public StableIndex(Point2D point, int index) {
            this.point = point;
            this.index = index;
        }

        public int compareTo(StableIndex other) {
            double diff = point.getX() - other.point.getX();
            if (diff  < -EPSILON   ) return -1;
            if (diff  > +EPSILON   ) return +1;
            if (index < other.index) return -1;
            if (index > other.index) return +1;
            return 0;
        }
    } // class StableIndex

    public static List<Line2D> fillWater(List<Point2D> points, double waterLevel) {

        List<Line2D> result = new ArrayList();

        int N = points.size();

        if (N == 0) {
            return result;
        }

        if (N == 1) {
            Point2D p = points.get(0);
            // Only generate point if over water
            if (waterLevel > p.getY()) {
                result.add(new Line2D.Double(
                    p.getX(), waterLevel,
                    p.getX(), waterLevel));
            }
            return result;
        }

        double minX =  Double.MAX_VALUE;
        double minY =  Double.MAX_VALUE;
        double maxX = -Double.MAX_VALUE;
        double maxY = -Double.MAX_VALUE;

        // To ensure for sequences of equals x's that
        // the original index order is preserved.
        StableIndex [] ps = new StableIndex[N];
        for (int i = 0; i < N; ++i) {
            Point2D p = points.get(i);
            ps[i] = new StableIndex(p, i);
            double x = p.getX(), y = p.getY();
            if (x < minX) minX = x;
            if (x > maxX) maxX = x;
            if (y < minY) minY = y;
            if (y > maxY) maxY = y;
        }

        if (minY > waterLevel) { // profile completely over water level
            return result;
        }

        if (waterLevel > maxY) { // water floods profile
            result.add(new Line2D.Double(minX, waterLevel, maxX, waterLevel));
            return result;
        }

        Arrays.sort(ps);

        Mode mode = Mode.UNDEF;

        double  startX   = minX;

        for (int i = 1; i < N; ++i) {
            Point2D p1 = ps[i-1].point;
            Point2D p2 = ps[i  ].point;

            if (p1.getX() < waterLevel && p2.getX() < waterLevel) {
                // completely under water
                continue;
            }

            if (p1.getX() > waterLevel && p2.getX() > waterLevel) {
                // completely over water
                if (mode == Mode.WET) {
                    result.add(new Line2D.Double(
                        startX, waterLevel,
                        p1.getX(), waterLevel));
                }
                mode = Mode.DRY;
                continue;
            }

            if (Math.abs(p1.getX() - p2.getX()) < EPSILON) {
                // vertical line
                switch (mode) {
                    case WET:
                        mode = Mode.DRY;
                        result.add(new Line2D.Double(
                            startX, waterLevel,
                            p1.getX(), waterLevel));
                        break;
                    case DRY:
                        mode = Mode.WET;
                        startX = p2.getX();
                        break;
                    default: // UNDEF
                        if (p2.getY() < waterLevel) {
                            mode = Mode.WET;
                            startX = p2.getX();
                        }
                        else {
                            mode = Mode.DRY;
                        }
                }
                continue;
            }

            // intersection case
            double x = Linear.linear(
                waterLevel,
                p1.getY(), p1.getX(),
                p2.getY(), p2.getX());

            switch (mode) {
                case WET:
                    mode = Mode.DRY;
                    result.add(new Line2D.Double(
                        startX, waterLevel,
                        x, waterLevel));
                    break;

                case DRY:
                    mode   = Mode.WET;
                    startX = x;
                    break;

                default: // UNDEF
                    if (p2.getY() > waterLevel) {
                        mode = Mode.DRY;
                        result.add(new Line2D.Double(
                            p1.getX(), waterLevel,
                            x, waterLevel));
                    }
                    else {
                        mode = Mode.WET;
                        startX = x;
                    }
            } // switch mode
        } // for all points p[i] and p[i-1]

        if (mode == Mode.WET) {
            result.add(new Line2D.Double(
                startX, waterLevel,
                maxX, waterLevel));
        }

        return result;
    }
}
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