// Runs the Python/trimesh sidecar scripts one at a time. Loading a large mesh
// can take hundreds of MB, so a preview conversion and background
// fingerprinting never run at once. Jobs someone is waiting on (previews) go
// ahead of queued background work.

const path = require('path');
const { execFile } = require('child_process');

const PYTHON = process.env.PYTHON_BIN || path.join(__dirname, '..', 'tools', 'venv', 'bin', 'python');
const TOOLS = path.join(__dirname, '..', 'tools');

const urgent = [];
const background = [];
let busy = false;

// Resolves { err, stdout, stderr } — never rejects, so callers can use partial
// output from a run that failed part-way.
function runScript(script, args, { timeout = 120000, isBackground = false } = {}) {
  return new Promise((resolve) => {
    (isBackground ? background : urgent).push({ script, args, timeout, resolve });
    next();
  });
}

function next() {
  if (busy) return;
  const job = urgent.shift() || background.shift();
  if (!job) return;
  busy = true;
  execFile(
    PYTHON,
    [path.join(TOOLS, job.script), ...job.args],
    { maxBuffer: 16 * 1024 * 1024, timeout: job.timeout },
    (err, stdout, stderr) => {
      busy = false;
      job.resolve({ err, stdout: String(stdout || ''), stderr: String(stderr || '') });
      next();
    }
  );
}

module.exports = { PYTHON, runScript };