'use strict';

/* ── Environment configuration & startup validation ───────────────────────
   Require this module BEFORE anything else that reads process.env.
   Fails fast with a clear message if required vars are missing or weak.
   ──────────────────────────────────────────────────────────────────────── */

require('dotenv').config({ path: require('path').join(__dirname, '../.env') });

const path   = require('path');
const errors = [];

function _require(key, { minLen, notValue } = {}) {
  const val = process.env[key];
  if (!val) { errors.push(`${key} is required`); return undefined; }
  if (minLen   && val.length < minLen)  errors.push(`${key} must be at least ${minLen} chars (got ${val.length})`);
  if (notValue && val === notValue)     errors.push(`${key} must not be the default placeholder value`);
  return val;
}

function _optional(key, defaultVal = undefined) {
  return process.env[key] || defaultVal;
}

/* ── Required vars ────────────────────────────────────────────────────── */
const JWT_SECRET = _require('JWT_SECRET', {
  minLen:   32,
  notValue: 'change_this_to_a_long_random_string',
});

/* ── Optional vars with defaults ─────────────────────────────────────── */
const NODE_ENV = _optional('NODE_ENV', 'development');
if (!['development', 'production', 'test'].includes(NODE_ENV)) {
  errors.push(`NODE_ENV must be development | production | test (got: "${NODE_ENV}")`);
}

const PORT_RAW = _optional('PORT', '3000');
const PORT = Number(PORT_RAW);
if (!Number.isInteger(PORT) || PORT < 1 || PORT > 65535) {
  errors.push(`PORT must be an integer between 1 and 65535 (got: "${PORT_RAW}")`);
}

/* ── Fail fast ───────────────────────────────────────────────────────── */
if (errors.length) {
  process.stderr.write('\n[config] FATAL: invalid environment configuration:\n');
  errors.forEach(e => process.stderr.write(`  ✗ ${e}\n`));
  process.stderr.write('\nFix these issues in your .env file and restart.\n\n');
  process.exit(1);
}

module.exports = Object.freeze({
  /* env */
  JWT_SECRET,
  PORT,
  NODE_ENV,
  isProd:        NODE_ENV === 'production',
  LOG_LEVEL:     _optional('LOG_LEVEL', NODE_ENV === 'production' ? 'info' : 'debug'),
  CLIENT_ORIGIN: _optional('CLIENT_ORIGIN'),
  /* paths */
  DB_PATH:       _optional('DB_PATH',     path.join(__dirname, '../data/learnspace.db')),
  UPLOADS_DIR:   _optional('UPLOADS_DIR', path.join(__dirname, '../uploads')),
  /* WebRTC ICE servers — TURN required for clients behind symmetric NAT/CGNAT (school networks) */
  TURN_URL:      _optional('TURN_URL'),       // e.g. turn:turn.example.com:3478
  TURN_USER:     _optional('TURN_USER'),
  TURN_PASS:     _optional('TURN_PASS'),
  /* constants */
  BCRYPT_ROUNDS: 12,
  MAX_FILE_SIZE: 50 * 1024 * 1024,
});