package com.whyc.util;

import com.whyc.dto.Point;

public class PointUtil {
    public static void main(String[] args) {
        int[] x = {0, 8, 8, 0}; // 四边形顶点x坐标
        int[] y = {0, 0, 8, 8}; // 四边形顶点y坐标
        int px = 9, py = 9; // 待检测点坐标

        if (isPointInQuadrilateral(px, py, x, y)) {
            System.out.println("点在四边形内或边上");
        } else {
            System.out.println("点在四边形外");
        }
    }

    /**
     * 判断点是否在四边形内或边上
     * @param px 待测点的x
     * @param py 待测点的y
     * @param x 四个点的x数组 四个点必须是顺时针顺序,从左下角开始顺时针
     * @param y 四个点的y数组
     * @return
     */
    public static boolean isPointInQuadrilateral(int px, int py, int[] x, int[] y) {
        int n = 4; // 四边形的边数

        // 检查点是否在顶点上
        for (int i = 0; i < n; i++) {
            if (px == x[i] && py == y[i]) {
                return true;
            }
        }

        // 检查点是否在边上
        for (int i = 0; i < n; i++) {
            int j = (i + 1) % n;
            if (isPointOnSegment(px, py, x[i], y[i], x[j], y[j])) {
                return true;
            }
        }

        // 使用射线法判断点是否在凸四边形内
        int intersections = 0;

        for (int i = 0; i < n; i++) {
            int j = (i + 1) % n;
            if (rayIntersectsSegment(px, py, x[i], y[i], x[j], y[j])) {
                intersections++;
            }
        }

        return intersections % 2 != 0;
    }

    private static boolean isPointOnSegment(int px, int py, int x1, int y1, int x2, int y2) {
        // 检查点是否在x1, y1 和 x2, y2 形成的线段上
        if (px < Math.min(x1, x2) || px > Math.max(x1, x2) || py < Math.min(y1, y2) || py > Math.max(y1, y2)) {
            return false;
        }

        // 向量叉积
        int crossProduct = (px - x1) * (y2 - y1) - (py - y1) * (x2 - x1);

        // 向量点积
        int dotProduct1 = (px - x1) * (x2 - x1) + (py - y1) * (y2 - y1);
        int dotProduct2 = (px - x2) * (x1 - x2) + (py - y2) * (y1 - y2);

        return crossProduct == 0 && dotProduct1 >= 0 && dotProduct2 >= 0;
    }

    private static boolean rayIntersectsSegment(int px, int py, int x1, int y1, int x2, int y2) {
        // 确保 y1 <= y2
        if (y1 > y2) {
            return rayIntersectsSegment(px, py, x2, y2, x1, y1);
        }

        // 射线不与线段平行且点在y范围内
        if (py > y1 && py <= y2) {
            // 计算交点x坐标
            //double xIntersection = (double) (px - x1) * (y2 - y1) / (double) (py - y1) + x1;
            double xIntersection = x1 + (double) (py - y1) * (x2 - x1) / (y2 - y1);

            // 射线从左到右，且交点在点的右侧
            return xIntersection >= px;
        }

        return false;
    }
}