/**
 * Deploy-level backup target policy (issue #192, ADR 0026). A backup
 * destination is an egress path for the full content of the instance, so
 * the set of permissible destination HOSTS is fixed at deploy time via
 * `BACKUP_ALLOWED_TARGETS` — a runtime setting could be widened by a
 * compromised Site-Admin account. An empty allowlist disables every
 * remote target (WebDAV and rsync mirror); "local only" is the VS-NfD
 * reference configuration. Both the api (settings writes, admin view) and
 * the backup sidecar (the actual egress) enforce the same policy through
 * these helpers.
 */

/** Comma-separated env value → normalized, deduplicated host list. */
export function parseBackupTargetAllowlist(raw: string): string[] {
  return [
    ...new Set(
      raw
        .split(',')
        .map((entry) => entry.trim().toLowerCase())
        .filter(Boolean),
    ),
  ];
}

/**
 * The destination host of a backup target: the hostname of a WebDAV URL,
 * or the host part of an rsync-over-ssh target (`user@host:/path`).
 * `null` for anything unparsable — which is never allowed.
 */
export function backupTargetHost(target: string): string | null {
  if (/^[a-z][a-z0-9+.-]*:\/\//i.test(target)) {
    try {
      const hostname = new URL(target).hostname;
      return hostname ? hostname.toLowerCase() : null;
    } catch {
      return null;
    }
  }
  const rsync = /^(?:[^@\s]+@)?([^/:@\s]+):/.exec(target);
  return rsync ? rsync[1]!.toLowerCase() : null;
}

/** Whether `target` points at an allowlisted host. Empty list ⇒ never. */
export function isBackupTargetAllowed(allowlist: string[], target: string): boolean {
  const host = backupTargetHost(target);
  return host !== null && allowlist.includes(host);
}