/**
 * src/utils/retry.ts
 *
 * Generic async retry helper with exponential backoff.
 * Used throughout the LLM pipeline where network flakiness is expected.
 */

import { logger } from './logger';

// ─── Types ────────────────────────────────────────────────────────────────────

export interface RetryOptions {
  /** Maximum number of retry attempts (not counting the initial try). */
  maxRetries: number;
  /** Base delay in milliseconds before first retry. */
  delayMs: number;
  /** Multiplier applied to delay on each subsequent retry. Default: 2 (exponential). */
  backoffMultiplier?: number;
  /** If provided, only retries when this predicate returns true. */
  retryOn?: (error: unknown) => boolean;
  /** Called just before each retry — useful for key rotation side effects. */
  onRetry?: (attempt: number, error: unknown) => void;
}

// ─── Core Retry Function ──────────────────────────────────────────────────────

/**
 * Executes `fn` up to `maxRetries + 1` times total, with exponential backoff.
 *
 * @example
 * const result = await withRetry(
 *   () => callLLM(prompt),
 *   { maxRetries: 3, delayMs: 1000, retryOn: isRateLimitError }
 * );
 */
export async function withRetry<T>(
  fn: () => Promise<T>,
  options: RetryOptions
): Promise<T> {
  const {
    maxRetries,
    delayMs,
    backoffMultiplier = 2,
    retryOn,
    onRetry,
  } = options;

  let lastError: unknown;

  for (let attempt = 1; attempt <= maxRetries + 1; attempt++) {
    try {
      return await fn();
    } catch (err) {
      lastError = err;

      // Don't retry if the error type is not eligible
      if (retryOn && !retryOn(err)) {
        throw err;
      }

      if (attempt > maxRetries) break; // Exhausted retries

      const delay = delayMs * Math.pow(backoffMultiplier, attempt - 1);
      onRetry?.(attempt, err);
      logger.warn(
        `withRetry: attempt ${attempt}/${maxRetries} failed. Retrying in ${delay}ms.`,
        { error: err instanceof Error ? err.message : String(err) }
      );
      await sleep(delay);
    }
  }

  throw lastError;
}

// ─── Rate-Limit Classifier ────────────────────────────────────────────────────

/**
 * Returns true if the error is a rate-limit response (HTTP 429).
 * Works with Groq SDK errors, Axios errors, and generic Error messages.
 */
export function isRateLimitError(err: unknown): boolean {
  if (err instanceof Error) {
    const msg = err.message.toLowerCase();
    // Covers: "429", "rate limit exceeded", "too many requests", "rate_limit_exceeded"
    if (msg.includes('429') || msg.includes('rate limit') || msg.includes('too many requests')) {
      return true;
    }
    // Groq SDK wraps status in the error object
    // eslint-disable-next-line @typescript-eslint/no-explicit-any
    const status = (err as any).status ?? (err as any).statusCode;
    if (status === 429) return true;
  }
  // Axios error
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  const axiosStatus = (err as any)?.response?.status;
  if (axiosStatus === 429) return true;

  return false;
}

// ─── Private Helpers ──────────────────────────────────────────────────────────

function sleep(ms: number): Promise<void> {
  return new Promise(resolve => setTimeout(resolve, ms));
}