import { ApiError } from "../api";

/**
 * Extract a user-friendly error message from an API error or generic error.
 * Handles ApiError instances with structured data, regular Error instances, and unknown errors.
 *
 * @param err - The error to extract a message from
 * @param fallback - Default message if extraction fails (default: "An error occurred")
 * @returns A user-friendly error message string
 */
export function extractApiErrorMessage(
  err: unknown,
  fallback: string = "An error occurred"
): string {
  if (err instanceof ApiError) {
    if (err.data && typeof err.data === "object") {
      const data = err.data as { detail?: string };
      return data.detail || err.message || fallback;
    }
    return err.message || fallback;
  }
  if (err instanceof Error) {
    return err.message;
  }
  return fallback;
}

/**
 * Type guard to check if an error is an ApiError with structured detail data.
 */
export function isApiErrorWithDetail(
  err: unknown
): err is ApiError & { data: { detail?: string } } {
  return err instanceof ApiError && err.data !== undefined && typeof err.data === "object";
}

/**
 * Extract field errors from a 422 validation error response.
 * Returns undefined if the error doesn't contain field errors.
 */
export function extractFieldErrors(
  err: unknown
): { detail?: { field_errors?: Record<string, string> } } | undefined {
  if (err instanceof ApiError && err.status === 422) {
    if (err.data && typeof err.data === "object") {
      return err.data as { detail?: { field_errors?: Record<string, string> } };
    }
  }
  return undefined;
}