import { adjacent, points, resultNumber } from './rules';
import { legalFlow } from './flow-rules';
import type { Ball } from './types';

export const balloonRadius = (n: number): number => 24 + Math.min(9, n - 1) * 3.2;
export const copyBalls = (balls: Ball[]): Ball[] => balls.map(b => ({ ...b }));
export interface Reaction { before: Ball[]; path: Ball[]; created: Ball; points: number; index: number }
export interface Cascade { stages: Reaction[]; balls: Ball[]; score: number; popped: number; flight: Ball | null }

/** 自动接上 n−2 → n−1 → 新球；新球一直留在玩家选择的链尾。 */
export function continuation(balls: Ball[], head: Ball): number[] | null {
  const seconds = balls.filter(b => b.n === head.n - 1 && adjacent(b, head))
    .sort((a, b) => Math.hypot(a.x - head.x, a.y - head.y) - Math.hypot(b.x - head.x, b.y - head.y));
  for (const second of seconds) {
    const first = balls.find(b => b.n === head.n - 2 && adjacent(b, second));
    if (first) return [first.id, second.id, head.id];
  }
  const same = balls.filter(b => b.id !== head.id && b.n === head.n);
  for (const second of same.filter(b => adjacent(b, head))) {
    const first = same.find(b => b.id !== second.id && adjacent(b, second));
    if (first) return [first.id, second.id, head.id];
  }
  return null;
}

export function cascade(source: Ball[], ids: number[], fever = false, offset = 0): Cascade | null {
  let balls = copyBalls(source), next: number[] | null = ids;
  const initial = ids.map(id => balls.find(b => b.id === id));
  if (initial.some(b => !b) || !legalFlow(initial as Ball[])) return null;
  const stages: Reaction[] = [];
  let score = 0, popped = 0, flight: Ball | null = null;
  while (next && stages.length + offset < (fever ? 4 : 3)) {
    const path = next.map(id => balls.find(b => b.id === id)!);
    const tail = path[path.length - 1], n = resultNumber(path), index = stages.length + offset + 1;
    const created = { ...tail, n, r: balloonRadius(n), vx: 0, vy: 0 };
    const gain = points(path) * index * (fever ? 2 : 1) + (n >= 10 ? 10000 : 0);
    stages.push({ before: copyBalls(balls), path: copyBalls(path), created: { ...created }, points: gain, index });
    score += gain; popped += path.length;
    const removed = new Set(next);
    balls = balls.filter(b => !removed.has(b.id));
    if (n >= 10) { flight = created; break; }
    balls.push(created);
    next = continuation(balls, created);
  }
  return { stages, balls, score, popped, flight };
}