type LockableInteraction = {
  user:        { id: string };
  customId:    string;
  deferUpdate(): Promise<any>;
};

const _processing = new Set<string>();

export async function withInteractionLock<T>(
  interaction: LockableInteraction,
  fn: () => Promise<T>
): Promise<T | null> {
  const key = `${interaction.user.id}:${interaction.customId}`;
  if (_processing.has(key)) {
    return null;
  }
  _processing.add(key);
  await interaction.deferUpdate();
  try {
    return await fn();
  } finally {
    _processing.delete(key);
  }
}

export const InteractionLock = {
  with: withInteractionLock,
  clear: () => _processing.clear(), // useful for testing
};