import { MAX_ERROR_COUNT } from '../utils/constants';

/**
 * The policy that decides what happens to a Feed after a fetch attempt:
 * how to categorize an error message, when to auto-deactivate the Feed
 * (ADR-0009: two-threshold deactivation), and how to reset on success.
 */

export type ErrorCategory = 'permanent' | 'transient' | 'unknown';

/** Permanent errors deactivate after this many consecutive failures. */
export const PERMANENT_ERROR_THRESHOLD = 3;

/** Transient and unknown errors share the higher (recoverable) threshold. */
export const TRANSIENT_ERROR_THRESHOLD = MAX_ERROR_COUNT;

const PERMANENT_PATTERN =
  /HTTP 404|HTTP 410|HTTP 403|Feed validation failed|Unable to identify feed|Attribute without value|Invalid character/i;
const TRANSIENT_PATTERN =
  /HTTP 5\d\d|HTTP 429|timed out|aborted|Unable to connect|unable to resolve|certificate|ECONNREFUSED|too large/i;

/**
 * Classify a fetch error message. Permanent errors mean the Feed is unlikely
 * to recover (gone, broken, malformed). Transient errors are recoverable
 * (server hiccups, network blips). Unknown means we don't have a rule yet —
 * treated as recoverable for threshold purposes.
 */
export function categorizeError(message: string): ErrorCategory {
  if (PERMANENT_PATTERN.test(message)) return 'permanent';
  if (TRANSIENT_PATTERN.test(message)) return 'transient';
  return 'unknown';
}

export interface ErrorPolicy {
  category: ErrorCategory;
  threshold: number;
}

/**
 * Return persistence policy for an already classified error. Error-count
 * advancement remains an atomic SQL concern in the Feed persistence seam.
 */
export function policyForErrorCategory(category: ErrorCategory): ErrorPolicy {
  const threshold = category === 'permanent' ? PERMANENT_ERROR_THRESHOLD : TRANSIENT_ERROR_THRESHOLD;
  return { category, threshold };
}

/**
 * State to apply to a Feed row after a successful fetch — clears the error
 * field and resets the consecutive-error counter.
 */
export function resetAfterSuccess(): { fetchError: null; errorCount: 0; errorCategory: null } {
  return { fetchError: null, errorCount: 0, errorCategory: null };
}