/**
 * metrics.js — 异步指标发射器 + 自动轮转 (P0-1)
 * 写入 debug/metrics-<category>.jsonl, >50MB 自动轮转保留 3 个
 */
'use strict';
const fs = require('fs');
const path = require('path');

let CLAUDE_ROOT;
try { CLAUDE_ROOT = require('./root.js'); } catch { CLAUDE_ROOT = path.resolve(__dirname, '..', '..'); }

const METRICS_DIR = path.join(CLAUDE_ROOT, 'debug');
const MAX_BYTES = 50 * 1024 * 1024;
const KEEP_ROTATED = 3;

function rotate(fp) {
  try {
    const s = fs.statSync(fp);
    if (s.size < MAX_BYTES) return;
    for (let i = KEEP_ROTATED; i >= 1; i--) {
      const dst = fp + '.' + i;
      if (i === KEEP_ROTATED) try { fs.unlinkSync(dst); } catch {}
      const src = i === 1 ? fp : fp + '.' + (i - 1);
      try { fs.renameSync(src, dst); } catch {}
    }
  } catch {}
}

function emit(category, data) {
  try {
    const fp = path.join(METRICS_DIR, 'metrics-' + category + '.jsonl');
    try { fs.mkdirSync(METRICS_DIR, { recursive: true }); } catch {}
    rotate(fp);
    const entry = Object.assign({ ts: new Date().toISOString() }, data);
    fs.appendFileSync(fp, JSON.stringify(entry) + '\n');
  } catch {}
}

module.exports = { emit, rotate };