/** 表单校验错误（key 对应 vue-i18n 文案） */
export class FormValidationError extends Error {
  readonly key: string;

  constructor(key: string) {
    super(key);
    this.name = 'FormValidationError';
    this.key = key;
  }
}

export function resolveFormError(e: unknown, t: (key: string) => string): string {
  if (e instanceof FormValidationError) return t(e.key);
  if (e instanceof Error && e.message.startsWith('err.')) return t(e.message);
  return t('msg.form_invalid');
}

/** Nest 默认 4xx 响应里 error 常为 "Bad Request" 等泛化文案，真实原因在 message */
const GENERIC_HTTP_ERRORS = new Set([
  'Bad Request',
  'Unauthorized',
  'Forbidden',
  'Not Found',
  'Conflict',
  'Unprocessable Entity',
  'Internal Server Error',
]);

/** 从 API 错误响应提取可读文案（兼容 GlobalExceptionFilter 与 Nest 默认格式） */
export function resolveApiError(
  err: unknown,
  t: (key: string) => string,
  fallbackKey = 'msg.save_failed',
): string {
  const data = (err as { response?: { data?: { error?: string | string[]; message?: string | string[] } } })
    ?.response?.data;
  const msgRaw = data?.message;
  const errRaw = data?.error;
  const message = Array.isArray(msgRaw) ? msgRaw.join('；') : msgRaw;
  const error = Array.isArray(errRaw) ? errRaw.join('；') : errRaw;
  if (typeof message === 'string' && message.trim()) {
    if (!error || GENERIC_HTTP_ERRORS.has(error)) return message;
  }
  if (typeof error === 'string' && error.trim() && !GENERIC_HTTP_ERRORS.has(error)) return error;
  return t(fallbackKey);
}