/***********************************************************************************************************************************************************************
 * File Name: certificate.service.js
 * Type of Program: Service
 * Description: Generates a PDF certificate by compiling a Typst template.
 *              Data is passed to the template via --input CLI flags (no temp files needed for input).
 *              Output is written to a temp file, read into a Buffer, then cleaned up.
 *
 * Author: Kenneth Obsequio (@lash0000)
 * Date Created: Jun. 18, 2026
 ***********************************************************************************************************************************************************************/
'use strict';

const { execFile }  = require('child_process');
const { promisify } = require('util');
const fs            = require('fs/promises');
const path          = require('path');
const crypto        = require('crypto');
const os            = require('os');

const execFileAsync = promisify(execFile);
const TEMPLATE_PATH = path.join(__dirname, '../templates/certificate.typ');

/**
 * @param {{
 *   name:        string,
 *   course:      string,
 *   date:        string,
 *   cert_no:     string,
 *   ref_no:      string,
 *   instructors?: string,
 *   length?:     string,
 * }} data
 * @returns {Promise<Buffer>}
 */
async function generateCertificate({ name, course, date, cert_no, ref_no, instructors = '', length = '' }) {
  const outPath = path.join(os.tmpdir(), `cert_${crypto.randomUUID()}.pdf`);

  const args = [
    'compile',
    TEMPLATE_PATH,
    outPath,
    '--input', `name=${name}`,
    '--input', `course=${course}`,
    '--input', `date=${date}`,
    '--input', `cert_no=${cert_no}`,
    '--input', `ref_no=${ref_no}`,
  ];

  if (instructors) args.push('--input', `instructors=${instructors}`);
  if (length)      args.push('--input', `length=${length}`);

  try {
    await execFileAsync('typst', args);
    return await fs.readFile(outPath);
  } finally {
    await fs.unlink(outPath).catch(() => {});
  }
}

module.exports = { generateCertificate };