const fs = require('node:fs/promises');
const path = require('node:path');

function delay(ms) {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

async function acquireFileLock(lockDir, options = {}) {
  const timeoutMs = Number(options.timeoutMs || 10 * 60 * 1000);
  const pollMs = Number(options.pollMs || 1000);
  const deadline = Date.now() + timeoutMs;
  const parent = path.dirname(lockDir);
  await fs.mkdir(parent, { recursive: true });

  while (Date.now() <= deadline) {
    try {
      await fs.mkdir(lockDir);
      await fs.writeFile(path.join(lockDir, 'owner.json'), JSON.stringify({
        pid: process.pid,
        acquiredAt: new Date().toISOString(),
      }, null, 2), 'utf8');
      return;
    } catch (error) {
      if (error && error.code !== 'EEXIST') throw error;
      if (await removeOrphanedLock(lockDir)) continue;
      await delay(pollMs);
    }
  }

  throw new Error(`Timed out waiting for ERP task lock: ${lockDir}`);
}

async function readLockOwner(lockDir) {
  try {
    const text = await fs.readFile(path.join(lockDir, 'owner.json'), 'utf8');
    const owner = JSON.parse(text);
    const pid = Number(owner && owner.pid);
    return Number.isInteger(pid) && pid > 0 ? { ...owner, pid } : null;
  } catch {
    return null;
  }
}

function processIsRunning(pid) {
  try {
    process.kill(pid, 0);
    return true;
  } catch (error) {
    if (error && error.code === 'ESRCH') return false;
    return true;
  }
}

async function removeOrphanedLock(lockDir) {
  const owner = await readLockOwner(lockDir);
  if (!owner || processIsRunning(owner.pid)) return false;
  await fs.rm(lockDir, { recursive: true, force: true });
  return true;
}

async function releaseFileLock(lockDir) {
  await fs.rm(lockDir, { recursive: true, force: true });
}

async function withFileLock(lockDir, fn, options = {}) {
  await acquireFileLock(lockDir, options);
  try {
    return await fn();
  } finally {
    await releaseFileLock(lockDir);
  }
}

module.exports = {
  acquireFileLock,
  releaseFileLock,
  withFileLock,
};