'use strict';

/**
 * 智能问数 · 统计异常检测工具
 * ----------------------------------------------------------------------------
 * detect_anomalies：对加性指标的逐日序列做 leave-one-out z-score 异常检测。
 * 方法论（模型无权偏离）：
 *   · 每天的 z = (当天值 - 其余天均值) / 其余天标准差（LOO，防异常值自己抬高 σ）
 *   · σ 下限 = 均值的 10%（防全同值序列除零误报）；样本 <5 天不检测
 *   · |z| ≥ 3 判 fail（严重异常），≥ 2 判 warn
 *   · 区间含寒暑假窗口（0108-0225 / 0701-0831）时附加 info 说明基线可能失真
 */

const metrics = require('../metrics.js');
const { eachDay, ymdDash } = require('./lake.js');

const VACATIONS = [
  { name: '寒假', from: '0108', to: '0225' },
  { name: '暑假', from: '0701', to: '0831' },
];

function std(values) {
  if (values.length < 2) return 0;
  const mean = values.reduce((s, x) => s + x, 0) / values.length;
  return Math.sqrt(values.reduce((s, x) => s + (x - mean) ** 2, 0) / (values.length - 1));
}

function mean(values) {
  return values.length ? values.reduce((s, x) => s + x, 0) / values.length : 0;
}

function anomalySanitize(args, ctx) {
  const a = args || {};
  const metric = ['grossAmt', 'validOrderCnt', 'incomeAmt', 'expUv', 'orderUserCnt'].includes(a.metric) ? a.metric : 'grossAmt';
  const { dateRange } = ctx;
  const from = /^\d{8}$/.test(String(a.from || '')) ? String(a.from) : dateRange.from;
  const to = /^\d{8}$/.test(String(a.to || '')) ? String(a.to) : dateRange.to;
  const k = Number(a.k) > 0 ? Number(a.k) : 2;
  return { metric, from: from < dateRange.from ? dateRange.from : from, to: to > dateRange.to ? dateRange.to : to, k };
}

function anomalyHandler(ctx, args) {
  const { svc, entityKey } = ctx;
  const { metric, from, to, k } = args;
  const def = metrics.get(metric) || {};
  const rows = svc.store.queryRows(entityKey, { from, to, scope: 'shop' });
  const byDate = new Map();
  for (const r of rows) {
    if (!byDate.has(r.date)) byDate.set(r.date, []);
    byDate.get(r.date).push(r);
  }
  const days = eachDay(from, to).filter((d) => byDate.has(d));
  if (days.length < 5) {
    return { summary: `异常检测需要至少 5 天数据（当前 ${days.length} 天），已跳过。`, data: { metric, from, to, anomalies: [], verdicts: [] } };
  }
  const series = days.map((d) => ({ date: d, value: metrics.dayValue(metric, byDate.get(d)) })).filter((s) => s.value != null);

  const anomalies = [];
  for (const s of series) {
    const others = series.filter((x) => x.date !== s.date).map((x) => x.value);
    const baseMean = mean(others);
    const sigma = Math.max(std(others), Math.abs(baseMean) * 0.1, 1); // σ 下限防全同值误报
    const z = (s.value - baseMean) / sigma;
    if (Math.abs(z) >= k) {
      anomalies.push({
        date: s.date, value: s.value, baseMean: Math.round(baseMean * 100) / 100,
        z: +z.toFixed(2), severity: Math.abs(z) >= 3 ? 'fail' : 'warn',
      });
    }
  }
  anomalies.sort((a, b) => Math.abs(b.z) - Math.abs(a.z));

  const lines = [`${def.name || metric} 异常检测（${ymdDash(from)} ~ ${ymdDash(to)}，leave-one-out z-score，阈值 |z|≥${k}）：`];
  if (!anomalies.length) {
    lines.push(`未发现统计异常（${series.length} 天均在基线 ±${k}σ 内）。`);
  } else {
    for (const a of anomalies.slice(0, 10)) {
      lines.push(`  [${a.severity}] ${ymdDash(a.date)}：${a.value}（基线 ${a.baseMean}，z=${a.z}）`);
    }
    if (anomalies.length > 10) lines.push(`  …其余 ${anomalies.length - 10} 天略`);
    lines.push('异常日建议结合活动/调价/天气等业务事件解读，再下结论。');
  }
  const mmdd = (v) => v.slice(4);
  const vacations = VACATIONS.filter((v) => {
    const f = mmdd(from);
    const t = mmdd(to);
    return (f >= v.from && f <= v.to) || (t >= v.from && t <= v.to) || (f < v.from && t > v.to);
  });
  if (vacations.length) {
    lines.push(`注意：区间含${vacations.map((v) => v.name).join('/')}窗口，基线可能失真，异常判定请谨慎采信。`);
  }

  const status = anomalies.some((a) => a.severity === 'fail') ? 'fail' : (anomalies.length ? 'warn' : 'ok');
  return {
    summary: lines.join('\n'),
    data: {
      metric, from, to, series, anomalies,
      verdicts: [{
        kind: 'anomaly', check: `统计异常 · ${def.name || metric}`,
        status,
        detail: anomalies.length
          ? `${anomalies.length} 天偏离基线（最差 ${ymdDash(anomalies[0].date)} z=${anomalies[0].z}）`
          : `${series.length} 天均在基线 ±${k}σ 内`,
      }],
    },
  };
}

module.exports = { anomalySanitize, anomalyHandler };