import type { Ball, Point } from './types';
import { canAppend } from './rules';

/** 同一控制器接 PointerEvent 或 Cocos EventTouch；取消不等于松手。 */
export class Gesture {
  chain: number[] = [];
  active = false;
  private previous: Point | null = null;
  constructor(private readonly balls: () => Ball[], private readonly append = canAppend) {}
  down(p: Point): void {
    this.cancel(); this.previous = p;
    const b = this.hit(p);
    if (b) { this.active = true; this.chain = [b.id]; }
  }
  move(p: Point): void {
    if (!this.active) return;
    const from = this.previous || p;
    // 分段采样避免快速扫过小球时跳号；一次事件最多 120 次。
    const steps = Math.min(120, Math.max(1, Math.ceil(Math.hypot(p.x - from.x, p.y - from.y) / 6)));
    for (let i = 1; i <= steps; i++) {
      const b = this.hit({ x: from.x + (p.x - from.x) * i / steps, y: from.y + (p.y - from.y) * i / steps });
      if (!b || b.id === this.chain[this.chain.length - 1]) continue;
      if (this.chain.length > 1 && b.id === this.chain[this.chain.length - 2]) { this.chain.pop(); continue; }
      const balls = this.balls();
      if (this.append(this.chain.map(id => balls.find(b => b.id === id)!), b)) this.chain.push(b.id);
    }
    this.previous = p;
  }
  up(): number[] { const path = [...this.chain]; this.cancel(); return path; }
  cancel(): void { this.chain = []; this.active = false; this.previous = null; }
  private hit(p: Point): Ball | undefined {
    return this.balls().filter(b => Math.hypot(b.x - p.x, b.y - p.y) <= b.r + 4)
      .sort((a, b) => Math.hypot(a.x - p.x, a.y - p.y) / a.r - Math.hypot(b.x - p.x, b.y - p.y) / b.r)[0];
  }
}