import fs from 'fs';

const results = [];

async function bench(name, fn, options = {}) {
  const iterations = options.iterations || 1;
  const warmup = options.warmup || 0;
  const unit = options.unit || 'ops/s';
  const itemsPerIter = options.itemsPerIter || null;

  for (let i = 0; i < warmup; i++) {
    await fn();
  }

  let totalTime = 0;
  for (let i = 0; i < iterations; i++) {
    const start = process.hrtime.bigint();
    await fn();
    const end = process.hrtime.bigint();
    totalTime += Number(end - start) / 1e6;
  }

  const avgTime = totalTime / iterations;
  const iterPerSec = 1000 / avgTime;
  const itemsPerSec = itemsPerIter ? Math.round(iterPerSec * itemsPerIter) : null;

  const resultEntry = {
    name,
    avgTimeMs: parseFloat(avgTime.toFixed(3)),
    iterPerSec: Math.round(iterPerSec),
    itemsPerSec,
    unit,
    itemsPerIter,
    samples: iterations,
    timestamp: new Date().toISOString()
  };

  results.push(resultEntry);

  return resultEntry;
}

async function run(options = {}) {
  const outputFile = options.output || './benchmark-results.json';
  const threshold = options.regressionThreshold || 0.9;

  const output = {
    timestamp: new Date().toISOString(),
    package: process.env.npm_package_name || 'unknown',
    version: process.env.npm_package_version || '0.0.0',
    node: process.version,
    benchmarks: results
  };

  if (fs.existsSync(outputFile)) {
    const previous = JSON.parse(fs.readFileSync(outputFile, 'utf8'));
    if (previous.benchmarks) {
      for (const newBench of results) {
        const prev = previous.benchmarks.find(b => b.name === newBench.name);
        if (prev) {
          const ratio = newBench.iterPerSec / prev.iterPerSec;
          newBench.regression = ratio < threshold;
          newBench.comparedToPrevious = {
            iterPerSec: prev.iterPerSec,
            ratio: parseFloat(ratio.toFixed(4))
          };
        }
      }
    }
  }

  const regression = results.some(b => b.regression);

  console.log('\nBenchmark Results:');
  console.log('-'.repeat(90));
  console.log(`${'Benchmark'.padEnd(50)} ${'Iter/s'.padStart(10)} ${'Items/s'.padStart(12)} Unit`);
  console.log('-'.repeat(90));
  for (const r of results) {
    const reg = r.regression ? ' [REGRESSION]' : '';
    const prev = r.comparedToPrevious ? ` (prev: ${r.comparedToPrevious.iterPerSec}, ratio: ${r.comparedToPrevious.ratio})` : '';
    const itemsRate = r.itemsPerSec ? r.itemsPerSec.toString().padStart(12) : '           -';
    console.log(`${r.name.padEnd(50)} ${r.iterPerSec.toString().padStart(10)} ${itemsRate} ${r.unit}${reg}${prev}`);
  }
  console.log('-'.repeat(90));

  if (outputFile) {
    fs.writeFileSync(outputFile, JSON.stringify(output, null, 2));
    console.log(`\nResults saved to: ${outputFile}`);
  }

  if (regression) {
    console.error('\nWARNING: Performance regression detected!');
    process.exit(1);
  }

  return results;
}

export { bench, run };