export function normalizeMattermostMessagingTarget(raw: string): string | undefined {
  const trimmed = raw.trim();
  if (!trimmed) {
    return undefined;
  }
  const lower = trimmed.toLowerCase();
  if (lower.startsWith("channel:")) {
    const id = trimmed.slice("channel:".length).trim();
    return id ? `channel:${id}` : undefined;
  }
  if (lower.startsWith("group:")) {
    const id = trimmed.slice("group:".length).trim();
    return id ? `channel:${id}` : undefined;
  }
  if (lower.startsWith("user:")) {
    const id = trimmed.slice("user:".length).trim();
    return id ? `user:${id}` : undefined;
  }
  if (lower.startsWith("mattermost:")) {
    const id = trimmed.slice("mattermost:".length).trim();
    return id ? `user:${id}` : undefined;
  }
  if (trimmed.startsWith("@")) {
    const id = trimmed.slice(1).trim();
    return id ? `@${id}` : undefined;
  }
  if (trimmed.startsWith("#")) {
    // Strip # prefix and fall through to directory lookup (same as bare names).
    // The core's resolveMessagingTarget will use the directory adapter to
    // resolve the channel name to its Mattermost ID.
    return undefined;
  }
  // Bare name without prefix — return undefined to allow directory lookup
  return undefined;
}

export function looksLikeMattermostTargetId(raw: string, normalized?: string): boolean {
  const trimmed = raw.trim();
  if (!trimmed) {
    return false;
  }
  if (/^(user|channel|group|mattermost):/i.test(trimmed)) {
    return true;
  }
  if (trimmed.startsWith("@")) {
    return true;
  }
  // Mattermost IDs: 26-char alnum, or DM channels like "abc123__xyz789" (53 chars)
  return /^[a-z0-9]{26}$/i.test(trimmed) || /^[a-z0-9]{26}__[a-z0-9]{26}$/i.test(trimmed);
}