/**
 * Stress test for the PDF export backend (/api/generate_pdf).
 *
 * Measures how many concurrent PDF exports the server can handle:
 *   - success rate
 *   - latency distribution (avg / p50 / p95 / max)
 *   - throughput (req/min)
 *
 * Usage:
 *   node stress/run-stress-test.js --base http://localhost:17861 --concurrency 1,2,4,6,8 --total 20 --profile medium
 *
 * Each concurrency level fires `total` requests in waves of `concurrency`
 * parallel requests. Between levels the server is given a rest period
 * (--settle-ms) so memory/CPU can drain back down.
 *
 * Output: JSON report written to stress/results/.
 */

const fs = require('fs');
const path = require('path');
const http = require('http');
const { prepareProfile } = require('./payload-generator');

function parseArgs(argv) {
  const args = { concurrency: '1,2,4,6,8', total: 20, base: 'http://localhost:17861', profile: 'medium', settleMs: 10000, tag: '', timeoutMs: 180000 };
  for (let i = 0; i < argv.length; i++) {
    const m = argv[i].match(/^--([^=]+)(?:=(.*))?$/);
    if (!m) continue;
    if (m[2] !== undefined) {
      args[m[1]] = m[2];
    } else if (i + 1 < argv.length && !argv[i + 1].startsWith('--')) {
      args[m[1]] = argv[++i];
    } else {
      args[m[1]] = true;
    }
  }
  return args;
}

function percentile(sorted, p) {
  if (sorted.length === 0) return 0;
  const idx = Math.min(sorted.length - 1, Math.ceil((p / 100) * sorted.length) - 1);
  return sorted[idx];
}

function sendPdfRequest(baseUrl, requestBody, timeoutMs) {
  const url = new URL('/api/generate_pdf', baseUrl);
  const payload = JSON.stringify(requestBody);
  return new Promise((resolve) => {
    const started = Date.now();
    const options = {
      hostname: url.hostname,
      port: url.port || 80,
      path: url.pathname,
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Content-Length': Buffer.byteLength(payload),
      },
      timeout: timeoutMs,
    };
    const req = http.request(options, (res) => {
      const chunks = [];
      res.on('data', (c) => chunks.push(c));
      res.on('end', () => {
        const elapsed = Date.now() - started;
        const body = Buffer.concat(chunks);
        if (res.statusCode === 200) {
          resolve({ ok: true, status: 200, elapsed, pdfBytes: body.length });
        } else {
          resolve({ ok: false, status: res.statusCode, elapsed, error: body.toString().substring(0, 500) });
        }
      });
      res.on('error', (e) => {
        resolve({ ok: false, status: 0, elapsed: Date.now() - started, error: e.message });
      });
    });
    req.on('error', (e) => {
      resolve({ ok: false, status: 0, elapsed: Date.now() - started, error: e.message });
    });
    req.on('timeout', () => {
      req.destroy(new Error(`timeout after ${timeoutMs}ms`));
    });
    req.write(payload);
    req.end();
  });
}

function fireWave(baseUrl, requestBody, concurrency, timeoutMs, onDone) {
  return new Promise((resolve) => {
    const results = [];
    let active = 0;
    let queued = concurrency;
    let done = 0;

    function startOne() {
      active++;
      sendPdfRequest(baseUrl, requestBody, timeoutMs).then((r) => {
        results.push(r);
        active--;
        done++;
        if (onDone) onDone(r);
        if (queued > 0) { queued--; startOne(); }
        else if (active === 0) resolve(results);
      });
    }
    for (let i = 0; i < concurrency && queued > 0; i++) { queued--; startOne(); }
  });
}

function sleep(ms) {
  return new Promise((r) => setTimeout(r, ms));
}

async function runConcurrencyLevel(baseUrl, requestBody, concurrency, total, timeoutMs, settleMs, onProgress) {
  const waves = Math.ceil(total / concurrency);
  const all = [];
  const startTs = Date.now();
  for (let w = 0; w < waves; w++) {
    const remaining = total - all.length;
    const thisWave = Math.min(concurrency, remaining);
    const waveResults = await fireWave(baseUrl, requestBody, thisWave, timeoutMs, onProgress);
    all.push(...waveResults);
  }
  const durationMs = Date.now() - startTs;
  await sleep(settleMs);
  return analyze(all, durationMs);
}

function analyze(results, durationMs) {
  const ok = results.filter((r) => r.ok);
  const fail = results.filter((r) => !r.ok);
  const latencies = ok.map((r) => r.elapsed).sort((a, b) => a - b);
  const totalOk = ok.length;
  const totalFail = fail.length;
  // Wall-clock throughput: requests actually completed per minute across the level.
  const rate = durationMs > 0 ? (totalOk / (durationMs / 60000)) : 0;

  const errorBreakdown = {};
  for (const f of fail) {
    const key = f.status === 500 ? '500' : (f.status === 0 ? 'conn/' + (f.error || 'unknown') : String(f.status));
    errorBreakdown[key] = (errorBreakdown[key] || 0) + 1;
  }

  return {
    totalRequests: results.length,
    success: totalOk,
    failed: totalFail,
    successRate: results.length ? (totalOk / results.length) : 0,
    latencyMs: {
      avg: latencies.length ? Math.round(latencies.reduce((a, b) => a + b, 0) / latencies.length) : 0,
      p50: percentile(latencies, 50),
      p90: percentile(latencies, 90),
      p95: percentile(latencies, 95),
      p99: percentile(latencies, 99),
      max: latencies.length ? latencies[latencies.length - 1] : 0,
      min: latencies.length ? latencies[0] : 0,
    },
    throughputPerMin: Math.round(rate),
    errorBreakdown,
    durationMs,
  };
}

async function main() {
  const args = parseArgs(process.argv.slice(2));
  const baseUrl = args.base.replace(/\/$/, '');
  const concurrencyLevels = args.concurrency.split(',').map((n) => parseInt(n, 10)).filter((n) => n > 0);
  const total = parseInt(args.total, 10);
  const timeoutMs = parseInt(args.timeoutMs, 10);
  const settleMs = parseInt(args.settleMs, 10);
  const profileName = args.profile;

  const profileDefs = {
    small: { name: 'small', opts: { textMB: 0.05, images: 0, codeRatio: 0.3 } },
    medium: { name: 'medium', opts: { textMB: 0.3, images: 3, codeRatio: 0.35 } },
    large: { name: 'large', opts: { textMB: 1.0, images: 10, codeRatio: 0.4 } },
  };
  const profileDef = profileDefs[profileName];
  if (!profileDef) {
    console.error(`Unknown profile: ${profileName}. Choose from ${Object.keys(profileDefs).join(', ')}`);
    process.exit(1);
  }

  const profile = prepareProfile(profileDef);
  const requestBody = { ...profile.requestBody, html: profile.html };
  console.log(`Profile: ${profileName}  html=${profile.htmlSizeMB.toFixed(3)} MB  text=${profile.textOnlySizeMB.toFixed(3)} MB  images=${profile.imageCount}`);
  console.log(`Base URL: ${baseUrl}`);
  console.log(`Concurrency levels: ${concurrencyLevels.join(', ')}  total/level: ${total}\n`);

  const report = {
    generatedAt: new Date().toISOString(),
    tag: args.tag,
    baseUrl,
    profile: { name: profileName, htmlSizeMB: profile.htmlSizeMB, textOnlySizeMB: profile.textOnlySizeMB, imageCount: profile.imageCount },
    concurrencyLevels,
    totalPerLevel: total,
    levels: {},
  };

  const allRequests = [];
  for (const conc of concurrencyLevels) {
    process.stdout.write(`\n=== Concurrency ${conc} (${total} requests) ===\n`);
    const level = await runConcurrencyLevel(baseUrl, requestBody, conc, total, timeoutMs, settleMs, (r) => {
      allRequests.push(r);
      process.stdout.write(r.ok ? '.' : 'X');
    });
    process.stdout.write('\n');
    report.levels[String(conc)] = level;
    const l = level;
    console.log(`  success=${l.success}/${l.totalRequests} (${(l.successRate * 100).toFixed(1)}%)  ` +
      `latency avg=${l.latencyMs.avg}ms p50=${l.latencyMs.p50}ms p95=${l.latencyMs.p95}ms max=${l.latencyMs.max}ms  ` +
      `throughput=${l.throughputPerMin}/min  errors=${JSON.stringify(l.errorBreakdown)}`);
  }

  // Summary table
  console.log('\n=== Summary ===');
  console.log('Concurrency | Success | Rate%  | avg(ms) | p50(ms) | p95(ms) | max(ms) | req/min |');
  console.log('------------|---------|--------|---------|---------|---------|---------|---------|');
  for (const conc of concurrencyLevels) {
    const l = report.levels[String(conc)];
    console.log(`${String(conc).padEnd(11)}| ${String(l.success).padEnd(8)}| ${(l.successRate * 100).toFixed(1).padEnd(7)}| ${String(l.latencyMs.avg).padEnd(8)}| ${String(l.latencyMs.p50).padEnd(8)}| ${String(l.latencyMs.p95).padEnd(8)}| ${String(l.latencyMs.max).padEnd(8)}| ${String(l.throughputPerMin).padEnd(8)}|`);
  }

  const stamp = new Date().toISOString().replace(/[:T]/g, '-').slice(0, 19);
  const tagSuffix = args.tag ? `-${args.tag}` : '';
  const outFile = path.join(__dirname, 'results', `stress-${profileName}${tagSuffix}-${stamp}.json`);
  fs.writeFileSync(outFile, JSON.stringify(report, null, 2));
  console.log(`\nReport saved: ${outFile}`);
}

main().catch((e) => {
  console.error(e);
  process.exit(1);
});