import type { Point } from '../types';

export function pointInPolygon(p: Point, poly: Point[]): boolean {
  if (poly.length < 3) return true;
  let inside = false;
  for (let i = 0, j = poly.length - 1; i < poly.length; j = i++) {
    const a = poly[i];
    const b = poly[j];
    if (onSegment(a, b, p)) return true;
    const intersect = a.y > p.y !== b.y > p.y && p.x < ((b.x - a.x) * (p.y - a.y)) / (b.y - a.y) + a.x;
    if (intersect) inside = !inside;
  }
  return inside;
}

function onSegment(a: Point, b: Point, p: Point): boolean {
  const cross = (b.x - a.x) * (p.y - a.y) - (b.y - a.y) * (p.x - a.x);
  if (Math.abs(cross) > 1e-9) return false;
  const dot = (p.x - a.x) * (b.x - a.x) + (p.y - a.y) * (b.y - a.y);
  if (dot < 0) return false;
  const len2 = (b.x - a.x) ** 2 + (b.y - a.y) ** 2;
  return dot <= len2;
}

function closestOnSegment(a: Point, b: Point, p: Point): Point {
  const dx = b.x - a.x;
  const dy = b.y - a.y;
  const len2 = dx * dx + dy * dy;
  if (len2 === 0) return { ...a };
  let t = ((p.x - a.x) * dx + (p.y - a.y) * dy) / len2;
  t = Math.max(0, Math.min(1, t));
  return { x: a.x + t * dx, y: a.y + t * dy };
}

export function nearestPointInPolygon(p: Point, poly: Point[]): Point {
  if (poly.length < 3) return { ...p };
  if (pointInPolygon(p, poly)) return { ...p };
  let best = poly[0];
  let bestD = Infinity;
  for (let i = 0, j = poly.length - 1; i < poly.length; j = i++) {
    const q = closestOnSegment(poly[j], poly[i], p);
    const d = (q.x - p.x) ** 2 + (q.y - p.y) ** 2;
    if (d < bestD) {
      bestD = d;
      best = q;
    }
  }
  return best;
}

export function rectanglePoints(width: number, height: number): Point[] {
  return [
    { x: 0, y: 0 },
    { x: width, y: 0 },
    { x: width, y: height },
    { x: 0, y: height },
  ];
}