/* 任务采样（方案 §4.3）：A 均匀 45% / B 直线被挡 30% / C 贴立柱 15% / D 目标不可达 10%；pos/pose 各半（D 只做 pos） */
'use strict';
/* 2026-10-18 第五轮（审查 N-16）：所有拒绝采样都有次数上限，超限抛错带原因（此前 for(;;) 在 collide.json 改动后可能静默死循环）。 */
const CAP = 200000;
function giveUp(what, n) { throw new Error(`采样失败：${what} 连续 ${n} 次未命中——多半是 collide.json / 关节限位变了，导致该类位形几乎不存在`); }
module.exports = function makeSampler(S, seed) {
  const L = S.LIM, O = S.ORDER, w = S.wrap180;
  let st = (seed >>> 0) || 1; const rnd = () => { st = (st * 1664525 + 1013904223) >>> 0; return st / 4294967296; };
  const rq = () => O.map(id => { const t = L[id]; return t.lo + rnd() * (t.hi - t.lo); });
  const d = (a, b) => a.map((v, i) => L[O[i]].cont ? w(b[i] - v) : b[i] - v);
  const segOK = (a, b) => { const dd = d(a, b); const n = Math.max(1, Math.ceil(Math.max(...dd.map(Math.abs)))); for (let i = 1; i <= n; i++) if (!S.collideFree(a.map((v, k) => v + dd[k] * i / n))) return false; return true; };
  const hitsColumn = q => (S.collideDetail(q) || []).some(p => /立柱/.test(p.cnA + p.cnB));
  const nearColumn = q => { for (const k of [0, 1, 2]) for (const sg of [-4, 4]) { const p = q.slice(); p[k] += sg; if (hitsColumn(p)) return true; } return false; };
  const freeQ = () => { for (let n = 0; n < CAP; n++) { const q = rq(); if (S.collideFree(q)) return q; } giveUp('无碰位形', CAP); };
  function sample() {
    const u = rnd();
    const cat = u < 0.45 ? 'A' : u < 0.75 ? 'B' : u < 0.90 ? 'C' : 'D';
    let a, b, T, R = null;
    if (cat === 'A') { a = freeQ(); b = freeQ(); }
    else if (cat === 'B') { let n = 0; for (;; n++) { if (n >= 20000) giveUp('B 类直线被挡', n); a = freeQ(); b = freeQ(); if (!segOK(a, b)) break; } }
    else if (cat === 'C') {
      let n = 0;
      for (;; n++) { if (n >= CAP) giveUp('C 类贴立柱终点', n); b = rq(); if (!S.collideFree(b) || !nearColumn(b)) continue; a = null;
        for (let t = 0; t < 200; t++) { const c = rq(); if (S.collideFree(c) && !segOK(c, b)) { a = c; break; } } if (a) break; }
    } else {
      a = freeQ();
      if (rnd() < 0.6) { let n = 0; for (;; n++) { if (n >= CAP) giveUp('D 类立柱内目标', n); b = rq(); if (hitsColumn(b)) break; } T = S.fk(b, 0); }    // 目标位置落在立柱附近/内部
      else { b = rq(); const p = S.fk(b, 0), o = S.fk(O.map(() => 0), 0); T = p.map((v, i) => o[i] + (v - o[i]) * 1.6); } // 工作空间外
    }
    const mode = cat === 'D' ? 'pos' : (rnd() < 0.5 ? 'pos' : 'pose');
    if (!T) T = S.fk(b, 0);
    if (mode === 'pose') R = S.orient(b);
    return { cat, mode, q0: a, T, R, qb: b };
  }
  const reseed = v => { st = (v >>> 0) || 1; };   // 2026-10-18：每条任务独立种子，shard 中断后可从第 i 条接着生成
  return { sample, rnd, segOK, reseed };
};