export type Point = {
  x: number;
  y: number;
};

export class DiamondCheck {
  // 计算两个向量的叉积的绝对值
  static crossProduct(a: Point, b: Point, p: Point): number {
    return (b.x - a.x) * (p.y - a.y) - (b.y - a.y) * (p.x - a.x);
  }

  // 判断点p是否在由顶点a, b, c, d定义的多边形内部
  static isPointInDiamond(
    point: Point,
    diamondCoords: [Point,Point,Point,Point]
  ): boolean {

    const [a,b,c,d] = diamondCoords;

    // 计算多边形的边
    const ab = { x: b.x - a.x, y: b.y - a.y };
    const bc = { x: c.x - b.x, y: c.y - b.y };
    const cd = { x: d.x - c.x, y: d.y - c.y };
    const da = { x: a.x - d.x, y: a.y - d.y };

    // 计算点p与多边形每条边的叉积
    const abP = DiamondCheck.crossProduct(a, b, point);
    const bcP = DiamondCheck.crossProduct(b, c, point);
    const cdP = DiamondCheck.crossProduct(c, d, point);
    const daP = DiamondCheck.crossProduct(d, a, point);

    // 如果所有叉积的符号一致（即绝对值相同），点p在多边形内部
    const allSameSign = (a: number, b: number, c: number, d: number): boolean =>
      Math.sign(a) === Math.sign(b) &&
      Math.sign(b) === Math.sign(c) &&
      Math.sign(c) === Math.sign(d);

    return allSameSign(abP, bcP, cdP, daP);
  }
}
