/**
 * @license
 * Copyright 2025 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import type { GenerateContentResponse } from '@google/genai';
import { ApiError } from '@google/genai';
import { AuthType } from '../core/contentGenerator.js';
import {
  classifyGoogleError,
  RetryableQuotaError,
  TerminalQuotaError,
} from './googleQuotaErrors.js';

const FETCH_FAILED_MESSAGE =
  'exception TypeError: fetch failed sending request';

export interface HttpError extends Error {
  status?: number;
}

export interface RetryOptions {
  maxAttempts: number;
  initialDelayMs: number;
  maxDelayMs: number;
  shouldRetryOnError: (error: Error, retryFetchErrors?: boolean) => boolean;
  shouldRetryOnContent?: (content: GenerateContentResponse) => boolean;
  onPersistent429?: (
    authType?: string,
    error?: unknown,
  ) => Promise<string | boolean | null>;
  authType?: string;
  retryFetchErrors?: boolean;
}

const DEFAULT_RETRY_OPTIONS: RetryOptions = {
  maxAttempts: 3,
  initialDelayMs: 5000,
  maxDelayMs: 30000, // 30 seconds
  shouldRetryOnError: defaultShouldRetry,
};

/**
 * Default predicate function to determine if a retry should be attempted.
 * Retries on 429 (Too Many Requests) and 5xx server errors.
 * @param error The error object.
 * @param retryFetchErrors Whether to retry on specific fetch errors.
 * @returns True if the error is a transient error, false otherwise.
 */
function defaultShouldRetry(
  error: Error | unknown,
  retryFetchErrors?: boolean,
): boolean {
  if (
    retryFetchErrors &&
    error instanceof Error &&
    error.message.includes(FETCH_FAILED_MESSAGE)
  ) {
    return true;
  }

  // Priority check for ApiError
  if (error instanceof ApiError) {
    // Explicitly do not retry 400 (Bad Request)
    if (error.status === 400) return false;
    return error.status === 429 || (error.status >= 500 && error.status < 600);
  }

  // Check for status using helper (handles other error shapes)
  const status = getErrorStatus(error);
  if (status !== undefined) {
    return status === 429 || (status >= 500 && status < 600);
  }

  return false;
}

/**
 * Delays execution for a specified number of milliseconds.
 * @param ms The number of milliseconds to delay.
 * @returns A promise that resolves after the delay.
 */
function delay(ms: number): Promise<void> {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

/**
 * Retries a function with exponential backoff and jitter.
 * @param fn The asynchronous function to retry.
 * @param options Optional retry configuration.
 * @returns A promise that resolves with the result of the function if successful.
 * @throws The last error encountered if all attempts fail.
 */
export async function retryWithBackoff<T>(
  fn: () => Promise<T>,
  options?: Partial<RetryOptions>,
): Promise<T> {
  if (options?.maxAttempts !== undefined && options.maxAttempts <= 0) {
    throw new Error('maxAttempts must be a positive number.');
  }

  const cleanOptions = options
    ? Object.fromEntries(Object.entries(options).filter(([_, v]) => v != null))
    : {};

  const {
    maxAttempts,
    initialDelayMs,
    maxDelayMs,
    onPersistent429,
    authType,
    shouldRetryOnError,
    shouldRetryOnContent,
    retryFetchErrors,
  } = {
    ...DEFAULT_RETRY_OPTIONS,
    ...cleanOptions,
  };

  let attempt = 0;
  let currentDelay = initialDelayMs;

  while (attempt < maxAttempts) {
    attempt++;
    try {
      const result = await fn();

      if (
        shouldRetryOnContent &&
        shouldRetryOnContent(result as GenerateContentResponse)
      ) {
        const jitter = currentDelay * 0.3 * (Math.random() * 2 - 1);
        const delayWithJitter = Math.max(0, currentDelay + jitter);
        await delay(delayWithJitter);
        currentDelay = Math.min(maxDelayMs, currentDelay * 2);
        continue;
      }

      return result;
    } catch (error) {
      const classifiedError = classifyGoogleError(error);

      if (classifiedError instanceof TerminalQuotaError) {
        if (onPersistent429 && authType === AuthType.LOGIN_WITH_GOOGLE) {
          try {
            const fallbackModel = await onPersistent429(
              authType,
              classifiedError,
            );
            if (fallbackModel) {
              attempt = 0; // Reset attempts and retry with the new model.
              currentDelay = initialDelayMs;
              continue;
            }
          } catch (fallbackError) {
            console.warn('Model fallback failed:', fallbackError);
          }
        }
        throw classifiedError; // Throw if no fallback or fallback failed.
      }

      if (classifiedError instanceof RetryableQuotaError) {
        if (attempt >= maxAttempts) {
          throw classifiedError;
        }
        console.warn(
          `Attempt ${attempt} failed: ${classifiedError.message}. Retrying after ${classifiedError.retryDelayMs}ms...`,
        );
        await delay(classifiedError.retryDelayMs);
        continue;
      }

      // Generic retry logic for other errors
      if (
        attempt >= maxAttempts ||
        !shouldRetryOnError(error as Error, retryFetchErrors)
      ) {
        throw error;
      }

      const errorStatus = getErrorStatus(error);
      logRetryAttempt(attempt, error, errorStatus);

      // Exponential backoff with jitter for non-quota errors
      const jitter = currentDelay * 0.3 * (Math.random() * 2 - 1);
      const delayWithJitter = Math.max(0, currentDelay + jitter);
      await delay(delayWithJitter);
      currentDelay = Math.min(maxDelayMs, currentDelay * 2);
    }
  }

  throw new Error('Retry attempts exhausted');
}

/**
 * Extracts the HTTP status code from an error object.
 * @param error The error object.
 * @returns The HTTP status code, or undefined if not found.
 */
export function getErrorStatus(error: unknown): number | undefined {
  if (typeof error === 'object' && error !== null) {
    if ('status' in error && typeof error.status === 'number') {
      return error.status;
    }
    // Check for error.response.status (common in axios errors)
    if (
      'response' in error &&
      typeof (error as { response?: unknown }).response === 'object' &&
      (error as { response?: unknown }).response !== null
    ) {
      const response = (
        error as { response: { status?: unknown; headers?: unknown } }
      ).response;
      if ('status' in response && typeof response.status === 'number') {
        return response.status;
      }
    }
  }
  return undefined;
}

/**
 * Logs a message for a retry attempt when using exponential backoff.
 * @param attempt The current attempt number.
 * @param error The error that caused the retry.
 * @param errorStatus The HTTP status code of the error, if available.
 */
function logRetryAttempt(
  attempt: number,
  error: unknown,
  errorStatus?: number,
): void {
  let message = `Attempt ${attempt} failed. Retrying with backoff...`;
  if (errorStatus) {
    message = `Attempt ${attempt} failed with status ${errorStatus}. Retrying with backoff...`;
  }

  if (errorStatus === 429) {
    console.warn(message, error);
  } else if (errorStatus && errorStatus >= 500 && errorStatus < 600) {
    console.error(message, error);
  } else if (error instanceof Error) {
    // Fallback for errors that might not have a status but have a message
    if (error.message.includes('429')) {
      console.warn(
        `Attempt ${attempt} failed with 429 error (no Retry-After header). Retrying with backoff...`,
        error,
      );
    } else if (error.message.match(/5\d{2}/)) {
      console.error(
        `Attempt ${attempt} failed with 5xx error. Retrying with backoff...`,
        error,
      );
    } else {
      console.warn(message, error); // Default to warn for other errors
    }
  } else {
    console.warn(message, error); // Default to warn if error type is unknown
  }
}