// Version history helpers for the CMS: listing automatic backups from
// .content-backups, safe backup-name validation and diff assembly.
const fs = require('fs');
const path = require('path');
const { renderDiffHtml } = require('./cms-diff');

// Backup files are named `<fileKey>.<ISO-ish timestamp>.json`
const BACKUP_NAME_RE = /^(\d{4}-\d{2}-\d{2})T(\d{2})-(\d{2})-(\d{2})-(\d{3})Z$/;

// WHY: the backup name arrives as a query parameter — only allow the exact
// `<fileKey>.<timestamp>.json` shape so path traversal (`../`) is impossible.
function safeBackupName(fileKey, candidate) {
  if (typeof candidate !== 'string' || !candidate.startsWith(`${fileKey}.`) || !candidate.endsWith('.json')) return null;
  const ts = candidate.slice(fileKey.length + 1, -5);
  if (!BACKUP_NAME_RE.test(ts)) return null;
  return candidate;
}

function formatBackupTimestamp(fileKey, backupName) {
  const ts = backupName.slice(fileKey.length + 1, -5);
  const m = ts.match(BACKUP_NAME_RE);
  if (!m) return ts;
  return `${m[1]} ${m[2]}:${m[3]}:${m[4]}`;
}

function listVersions(backupDir, fileKey) {
  try {
    return fs.readdirSync(backupDir)
      .filter(name => safeBackupName(fileKey, name))
      .map(name => {
        const full = path.join(backupDir, name);
        const stat = fs.statSync(full);
        return { name, size: stat.size, when: formatBackupTimestamp(fileKey, name) };
      })
      .sort((a, b) => b.name.localeCompare(a.name)); // newest first
  } catch {
    return [];
  }
}

function readBackupContent(backupDir, backupName) {
  return fs.readFileSync(path.join(backupDir, backupName), 'utf8');
}

// Compare a backup with the current file content; returns both pretty texts and
// the rendered diff HTML (backup = old/left, current = new/right).
function buildVersionDiff(backupDir, currentFilePath, fileKey, backupName) {
  const backupText = readBackupContent(backupDir, backupName);
  const currentText = fs.readFileSync(currentFilePath, 'utf8');
  return {
    backupName,
    when: formatBackupTimestamp(fileKey, backupName),
    backupText: backupText.trim(),
    currentText: currentText.trim(),
    diffHtml: renderDiffHtml(backupText, currentText),
  };
}

module.exports = { safeBackupName, listVersions, readBackupContent, buildVersionDiff, formatBackupTimestamp };