import LogicFlow from '../LogicFlow'

import Point = LogicFlow.Point

/**
 * 求两个线段交点入参：线段1端点: ab, 线段2端点： cd,
 * @param a
 * @param b
 * @param c
 * @param d
 * @return：有交点返回交点 Point，无交点返回false
 */
export const getCrossPointOfLine = (a: Point, b: Point, c: Point, d: Point) => {
  /** 1 解线性方程组, 求线段交点. * */
  // 如果分母为0 则平行或共线, 不相交
  const denominator = (b.y - a.y) * (d.x - c.x) - (a.x - b.x) * (c.y - d.y)
  if (denominator === 0) {
    return false
  }
  // 线段所在直线的交点坐标 (x , y)
  const x =
    ((b.x - a.x) * (d.x - c.x) * (c.y - a.y) +
      (b.y - a.y) * (d.x - c.x) * a.x -
      (d.y - c.y) * (b.x - a.x) * c.x) /
    denominator
  const y =
    -(
      (b.y - a.y) * (d.y - c.y) * (c.x - a.x) +
      (b.x - a.x) * (d.y - c.y) * a.y -
      (d.x - c.x) * (b.y - a.y) * c.y
    ) / denominator

  /** 2 判断交点是否在两条线段上 * */
  if (
    // 交点在线段1上
    (x - a.x) * (x - b.x) <= 0 &&
    (y - a.y) * (y - b.y) <= 0 &&
    // 且交点也在线段2上
    (x - c.x) * (x - d.x) <= 0 &&
    (y - c.y) * (y - d.y) <= 0
  ) {
    // 返回交点p
    return {
      x,
      y,
    }
  }
  // 否则不相交
  return false
}

/* 判断一个点是否在线段中
入参点：point, 线段起终点，start,end,
返回值： 在线段中true，否则false
*/
export const isInSegment = (point: Point, start: Point, end: Point) => {
  const { x, y } = point
  const { x: startX, y: startY } = start
  const { x: endX, y: endY } = end
  const k = (endY - startY) / (endX - startX)
  const b = startY - k * startX
  return (
    ((x >= startX && x <= endX) || (x <= startX && x >= endX)) &&
    ((y >= startY && y <= endY) || (y <= startY && y >= endY)) &&
    Math.abs(y - k * x - b) < Number.EPSILON
  )
}