// Security and infrastructure helpers for the Content Editor, extracted so
// content-editor.js stays focused on HTTP routing (file-size limits).
// Dependencies (validateLogin, hasValidSession) are injected to avoid cycles.
const crypto = require('crypto');
const fs = require('fs');
const path = require('path');

const CMS_USER = process.env.CMS_USER;
const CMS_PASS = process.env.CMS_PASS;
const CMS_DEPLOY_ENV = process.env.CMS_DEPLOY_ENV;
const CSRF_TOKEN = process.env.CMS_CSRF_TOKEN || crypto.randomBytes(32).toString('hex');
const rateLimits = new Map();

function securityConfigIsValid() {
  return Boolean(CMS_USER && CMS_PASS && ['staging', 'production'].includes(CMS_DEPLOY_ENV));
}

function getClientAddress(req) {
  // The editor only listens on 127.0.0.1; the staging Nginx proxy supplies this header.
  // WHY: take the LAST entry. Nginx ($proxy_add_x_forwarded_for) appends the real client
  // IP to the list, so the first entry may be a spoofed value sent by the client — using
  // it would let attackers bypass the rate limiter with a fresh "IP" per request.
  const forwarded = req.headers['x-forwarded-for'];
  if (typeof forwarded === 'string' && forwarded.trim()) {
    const parts = forwarded.split(',').map(part => part.trim()).filter(Boolean);
    if (parts.length > 0) return parts[parts.length - 1];
  }
  return req.socket.remoteAddress || 'unknown';
}

function isRateLimited(key, limit, windowMs) {
  const now = Date.now();
  const attempts = (rateLimits.get(key) || []).filter(time => now - time < windowMs);
  if (attempts.length === 0) {
    rateLimits.delete(key);
    return false;
  }
  rateLimits.set(key, attempts);
  return attempts.length >= limit;
}

function recordRateLimitAttempt(key, windowMs) {
  const now = Date.now();
  const attempts = (rateLimits.get(key) || []).filter(time => now - time < windowMs);
  attempts.push(now);
  rateLimits.set(key, attempts);
}

function exceedsRateLimit(key, limit, windowMs) {
  const now = Date.now();
  const attempts = (rateLimits.get(key) || []).filter(time => now - time < windowMs);
  attempts.push(now);
  rateLimits.set(key, attempts);
  return attempts.length > limit;
}

function hasValidCredentials(req, validateLogin) {
  const b64auth = (req.headers.authorization || '').split(' ')[1] || '';
  const str = Buffer.from(b64auth, 'base64').toString();
  const colonIdx = str.indexOf(':');
  const login = colonIdx !== -1 ? str.slice(0, colonIdx) : str;
  const password = colonIdx !== -1 ? str.slice(colonIdx + 1) : '';
  return validateLogin(login, password, CMS_USER, CMS_PASS);
}

function isBrowserNavigation(req) {
  return req.method === 'GET' && String(req.headers.accept || '').includes('text/html');
}

// WHY: Safari (and other browsers) cache Basic Auth credentials and resend them
// automatically, which would let an already-logged-out browser straight back in.
// Browser navigations therefore authenticate ONLY via the session cookie, so
// logout is final. Non-browser requests (curl, API clients) keep Basic Auth.
function makeIsAuthenticated(hasValidSession, validateLogin) {
  return function isAuthenticated(req) {
    if (isBrowserNavigation(req)) return hasValidSession(req);
    return hasValidCredentials(req, validateLogin) || hasValidSession(req);
  };
}

function hasValidCsrfToken(req) {
  const token = req.headers['x-csrf-token'];
  return typeof token === 'string'
    && token.length === CSRF_TOKEN.length
    && crypto.timingSafeEqual(Buffer.from(token), Buffer.from(CSRF_TOKEN));
}

function makeWriteAudit(auditFile) {
  return function writeAudit(event, details = {}) {
    const record = { timestamp: new Date().toISOString(), event, ...details };
    fs.appendFileSync(auditFile, JSON.stringify(record) + '\n', { encoding: 'utf8', mode: 0o600 });
  };
}

function backupAndWriteAtomically(targetFile, data, backupDir) {
  const timestamp = new Date().toISOString().replace(/[:.]/g, '-');
  const backupName = `${path.basename(targetFile, '.json')}.${timestamp}.json`;
  const backupFile = path.join(backupDir, backupName);
  const tempFile = `${targetFile}.${process.pid}.${Date.now()}.tmp`;

  fs.mkdirSync(backupDir, { recursive: true, mode: 0o700 });
  fs.copyFileSync(targetFile, backupFile);
  fs.writeFileSync(tempFile, JSON.stringify(data, null, 2) + '\n', { encoding: 'utf8', mode: 0o600 });
  fs.renameSync(tempFile, targetFile);
  return backupFile;
}


const RATE_LIMIT_GC_INTERVAL_MS = 5 * 60 * 1000;
setInterval(() => {
  const now = Date.now();
  for (const [key, attempts] of rateLimits) {
    const valid = attempts.filter(t => now - t < 15 * 60 * 1000);
    if (valid.length === 0) rateLimits.delete(key);
    else rateLimits.set(key, valid);
  }
}, RATE_LIMIT_GC_INTERVAL_MS).unref();

module.exports = {
  CMS_USER,
  CMS_PASS,
  CMS_DEPLOY_ENV,
  CSRF_TOKEN,
  securityConfigIsValid,
  getClientAddress,
  isRateLimited,
  recordRateLimitAttempt,
  exceedsRateLimit,
  hasValidCredentials,
  isBrowserNavigation,
  makeIsAuthenticated,
  hasValidCsrfToken,
  makeWriteAudit,
  backupAndWriteAtomically,
};