/**
 * Network Error Recovery Utilities
 *
 * Provides robust network error handling with:
 * - Request timeout handling
 * - Circuit breaker pattern to prevent cascading failures
 * - Automatic retry with exponential backoff
 * - Request deduplication for concurrent calls
 */

import { ApiError, ApiResponse } from '@/types';
import { isOnline } from './networkStatus';
import { ErrorCodes } from '@/types/errors';

// ==================== Configuration ====================

/**
 * Default request timeout (30 seconds)
 */
export const DEFAULT_REQUEST_TIMEOUT = 30000;

/**
 * Short timeout for quick operations (10 seconds)
 */
export const SHORT_REQUEST_TIMEOUT = 10000;

/**
 * Long timeout for uploads and heavy operations (60 seconds)
 */
export const LONG_REQUEST_TIMEOUT = 60000;

// ==================== Timeout Handling ====================

/**
 * AbortController with timeout
 * Creates an AbortController that automatically aborts after the specified timeout
 *
 * @param timeoutMs - Timeout in milliseconds
 * @returns Object with signal and cleanup function
 *
 * @example
 * const { signal, cleanup } = createTimeoutController(10000);
 * try {
 *   const response = await fetch(url, { signal });
 *   cleanup();
 * } catch (e) {
 *   cleanup();
 *   if (e.name === 'AbortError') {
 *     // Handle timeout
 *   }
 * }
 */
export function createTimeoutController(timeoutMs: number = DEFAULT_REQUEST_TIMEOUT): {
  controller: AbortController;
  signal: AbortSignal;
  cleanup: () => void;
  isTimedOut: () => boolean;
} {
  const controller = new AbortController();
  let timedOut = false;

  const timeoutId = setTimeout(() => {
    timedOut = true;
    controller.abort();
  }, timeoutMs);

  const cleanup = () => {
    clearTimeout(timeoutId);
  };

  return {
    controller,
    signal: controller.signal,
    cleanup,
    isTimedOut: () => timedOut,
  };
}

/**
 * Wrap fetch with timeout support
 *
 * @param url - Request URL
 * @param options - Fetch options
 * @param timeoutMs - Timeout in milliseconds
 * @returns Promise with Response
 * @throws Error with code NETWORK_TIMEOUT if request times out
 *
 * @example
 * try {
 *   const response = await fetchWithTimeout('https://api.example.com', { method: 'GET' }, 10000);
 *   const data = await response.json();
 * } catch (e) {
 *   if (e.code === 'NETWORK_TIMEOUT') {
 *     // Handle timeout
 *   }
 * }
 */
export async function fetchWithTimeout(
  url: string,
  options: RequestInit = {},
  timeoutMs: number = DEFAULT_REQUEST_TIMEOUT
): Promise<Response> {
  const { signal, cleanup, isTimedOut } = createTimeoutController(timeoutMs);

  try {
    // Merge signals if one was already provided
    const mergedOptions: RequestInit = {
      ...options,
      signal: options.signal
        ? anySignal([options.signal, signal])
        : signal,
    };

    const response = await fetch(url, mergedOptions);
    cleanup();
    return response;
  } catch (error) {
    cleanup();

    // Check if this was a timeout
    if (isTimedOut() || (error instanceof Error && error.name === 'AbortError')) {
      const timeoutError = new Error(`Request timed out after ${timeoutMs}ms`);
      (timeoutError as any).code = ErrorCodes.NETWORK_TIMEOUT;
      (timeoutError as any).name = 'TimeoutError';
      throw timeoutError;
    }

    throw error;
  }
}

/**
 * Combine multiple AbortSignals into one
 * The combined signal aborts when any of the input signals abort
 */
function anySignal(signals: AbortSignal[]): AbortSignal {
  const controller = new AbortController();

  for (const signal of signals) {
    if (signal.aborted) {
      controller.abort();
      return controller.signal;
    }
    signal.addEventListener('abort', () => controller.abort(), { once: true });
  }

  return controller.signal;
}

// ==================== Circuit Breaker ====================

/**
 * Circuit breaker states
 */
type CircuitState = 'closed' | 'open' | 'half-open';

/**
 * Circuit breaker configuration
 */
interface CircuitBreakerConfig {
  /** Number of failures before opening circuit */
  failureThreshold: number;
  /** Time to wait before trying again (ms) */
  resetTimeout: number;
  /** Number of successes needed to close circuit from half-open */
  successThreshold: number;
}

/**
 * Default circuit breaker configuration
 */
const DEFAULT_CIRCUIT_CONFIG: CircuitBreakerConfig = {
  failureThreshold: 5,
  resetTimeout: 30000, // 30 seconds
  successThreshold: 2,
};

/**
 * Circuit breaker state storage
 */
interface CircuitBreakerState {
  state: CircuitState;
  failures: number;
  successes: number;
  lastFailure: number | null;
  lastStateChange: number;
}

/**
 * Circuit breakers by endpoint key
 */
const circuits = new Map<string, CircuitBreakerState>();

/**
 * Get or create circuit breaker state for a key
 */
function getCircuit(key: string): CircuitBreakerState {
  if (!circuits.has(key)) {
    circuits.set(key, {
      state: 'closed',
      failures: 0,
      successes: 0,
      lastFailure: null,
      lastStateChange: Date.now(),
    });
  }
  return circuits.get(key)!;
}

/**
 * Check if circuit is allowing requests
 */
export function isCircuitOpen(key: string, config: CircuitBreakerConfig = DEFAULT_CIRCUIT_CONFIG): boolean {
  const circuit = getCircuit(key);

  if (circuit.state === 'open') {
    // Check if enough time has passed to try again
    const now = Date.now();
    if (now - circuit.lastStateChange >= config.resetTimeout) {
      // Transition to half-open
      circuit.state = 'half-open';
      circuit.successes = 0;
      circuit.lastStateChange = now;
      return false;
    }
    return true;
  }

  return false;
}

/**
 * Record a successful request
 */
export function recordSuccess(key: string, config: CircuitBreakerConfig = DEFAULT_CIRCUIT_CONFIG): void {
  const circuit = getCircuit(key);

  if (circuit.state === 'half-open') {
    circuit.successes++;
    if (circuit.successes >= config.successThreshold) {
      // Close the circuit
      circuit.state = 'closed';
      circuit.failures = 0;
      circuit.successes = 0;
      circuit.lastStateChange = Date.now();
    }
  } else if (circuit.state === 'closed') {
    // Reset failure count on success
    circuit.failures = 0;
  }
}

/**
 * Record a failed request
 */
export function recordFailure(key: string, config: CircuitBreakerConfig = DEFAULT_CIRCUIT_CONFIG): void {
  const circuit = getCircuit(key);
  const now = Date.now();

  circuit.failures++;
  circuit.lastFailure = now;

  if (circuit.state === 'half-open') {
    // Any failure in half-open state opens the circuit
    circuit.state = 'open';
    circuit.lastStateChange = now;
  } else if (circuit.state === 'closed' && circuit.failures >= config.failureThreshold) {
    // Open the circuit
    circuit.state = 'open';
    circuit.lastStateChange = now;
  }
}

/**
 * Get current circuit state for debugging
 */
export function getCircuitState(key: string): CircuitBreakerState {
  return getCircuit(key);
}

/**
 * Reset circuit breaker (for testing or manual recovery)
 */
export function resetCircuit(key: string): void {
  circuits.delete(key);
}

/**
 * Reset all circuits
 */
export function resetAllCircuits(): void {
  circuits.clear();
}

// ==================== Request Deduplication ====================

/**
 * In-flight request cache for deduplication
 */
const inflightRequests = new Map<string, Promise<any>>();

/**
 * Generate a cache key for a request
 */
export function generateRequestKey(method: string, url: string, body?: string): string {
  const bodyHash = body ? simpleHash(body) : '';
  return `${method}:${url}:${bodyHash}`;
}

/**
 * Simple hash function for request body
 */
function simpleHash(str: string): string {
  let hash = 0;
  for (let i = 0; i < str.length; i++) {
    const char = str.charCodeAt(i);
    hash = ((hash << 5) - hash) + char;
    hash = hash & hash; // Convert to 32bit integer
  }
  return hash.toString(36);
}

/**
 * Deduplicate concurrent identical requests
 * If a request with the same key is already in flight, return the same promise
 *
 * @param key - Unique key for the request
 * @param request - Function that returns the request promise
 * @returns Promise with the result
 *
 * @example
 * // Both calls will use the same underlying request
 * const [result1, result2] = await Promise.all([
 *   deduplicateRequest('get-user-1', () => api.getUser(1)),
 *   deduplicateRequest('get-user-1', () => api.getUser(1)),
 * ]);
 */
export async function deduplicateRequest<T>(
  key: string,
  request: () => Promise<T>
): Promise<T> {
  // Check if request is already in flight
  const existing = inflightRequests.get(key);
  if (existing) {
    return existing;
  }

  // Create new request and cache it
  const promise = request().finally(() => {
    // Remove from cache when complete
    inflightRequests.delete(key);
  });

  inflightRequests.set(key, promise);
  return promise;
}

// ==================== Enhanced Fetch with All Features ====================

/**
 * Options for network-aware fetch
 */
export interface NetworkAwareFetchOptions extends RequestInit {
  /** Request timeout in milliseconds */
  timeout?: number;
  /** Circuit breaker key (defaults to URL host) */
  circuitKey?: string;
  /** Enable request deduplication for GET requests */
  deduplicate?: boolean;
  /** Number of retry attempts */
  retries?: number;
  /** Base delay between retries in ms */
  retryDelay?: number;
  /** Multiplier for exponential backoff */
  retryBackoff?: number;
}

/**
 * Enhanced fetch with timeout, circuit breaker, and retry support
 *
 * @param url - Request URL
 * @param options - Enhanced fetch options
 * @returns Promise with Response
 *
 * @example
 * const response = await networkAwareFetch('https://api.example.com/data', {
 *   method: 'GET',
 *   timeout: 10000,
 *   retries: 3,
 *   deduplicate: true,
 * });
 */
export async function networkAwareFetch(
  url: string,
  options: NetworkAwareFetchOptions = {}
): Promise<Response> {
  const {
    timeout = DEFAULT_REQUEST_TIMEOUT,
    circuitKey = new URL(url).host,
    deduplicate = false,
    retries = 0,
    retryDelay = 1000,
    retryBackoff = 2,
    ...fetchOptions
  } = options;

  // Check if circuit is open
  if (isCircuitOpen(circuitKey)) {
    const error = new Error('Service temporarily unavailable due to repeated failures');
    (error as any).code = ErrorCodes.SERVICE_UNAVAILABLE;
    throw error;
  }

  // Check network status
  const online = await isOnline();
  if (!online) {
    const error = new Error('No internet connection');
    (error as any).code = ErrorCodes.NETWORK_OFFLINE;
    throw error;
  }

  // Create the actual fetch function
  const doFetch = async (): Promise<Response> => {
    try {
      const response = await fetchWithTimeout(url, fetchOptions, timeout);

      // Record success if response is OK
      if (response.ok) {
        recordSuccess(circuitKey);
      } else if (response.status >= 500) {
        // Server errors trigger circuit breaker
        recordFailure(circuitKey);
      }

      return response;
    } catch (error) {
      recordFailure(circuitKey);
      throw error;
    }
  };

  // Handle deduplication for GET requests
  const method = (fetchOptions.method || 'GET').toUpperCase();
  if (deduplicate && method === 'GET') {
    const key = generateRequestKey(method, url);
    return deduplicateRequest(key, doFetch);
  }

  // Execute with retries if configured
  if (retries > 0) {
    return executeWithRetry(doFetch, retries, retryDelay, retryBackoff);
  }

  return doFetch();
}

/**
 * Execute a function with retry support
 */
async function executeWithRetry<T>(
  fn: () => Promise<T>,
  maxRetries: number,
  baseDelay: number,
  backoffMultiplier: number
): Promise<T> {
  let lastError: Error | undefined;
  let delay = baseDelay;

  for (let attempt = 0; attempt <= maxRetries; attempt++) {
    try {
      return await fn();
    } catch (error) {
      lastError = error instanceof Error ? error : new Error(String(error));

      // Check if error is retryable
      const errorCode = (error as any)?.code;
      const isRetryable =
        errorCode === ErrorCodes.NETWORK_TIMEOUT ||
        errorCode === ErrorCodes.NETWORK_ERROR ||
        errorCode === ErrorCodes.SERVICE_UNAVAILABLE;

      if (!isRetryable || attempt === maxRetries) {
        throw lastError;
      }

      // Wait before retry
      await new Promise(resolve => setTimeout(resolve, delay));
      delay *= backoffMultiplier;
    }
  }

  throw lastError || new Error('Max retries exceeded');
}

// ==================== API Response Helpers ====================

/**
 * Create an error response for network issues
 */
export function createNetworkErrorResponse<T>(
  code: string,
  message: string
): ApiResponse<T> {
  return {
    ok: false,
    error: {
      message,
      code,
    },
  };
}

/**
 * Check if an error is a timeout error
 */
export function isTimeoutError(error: unknown): boolean {
  if (error instanceof Error) {
    return (
      (error as any).code === ErrorCodes.NETWORK_TIMEOUT ||
      error.name === 'TimeoutError' ||
      error.name === 'AbortError' ||
      error.message.includes('timeout')
    );
  }
  return false;
}

/**
 * Check if an error is a network error
 */
export function isNetworkError(error: unknown): boolean {
  if (error instanceof Error) {
    const code = (error as any).code;
    return (
      code === ErrorCodes.NETWORK_ERROR ||
      code === ErrorCodes.NETWORK_OFFLINE ||
      code === ErrorCodes.NETWORK_TIMEOUT ||
      error.message.toLowerCase().includes('network') ||
      error.message.toLowerCase().includes('fetch')
    );
  }
  return false;
}

/**
 * Get appropriate error code from an error
 */
export function getErrorCode(error: unknown): string {
  if (error instanceof Error) {
    const code = (error as any).code;
    if (code) return code;

    if (isTimeoutError(error)) return ErrorCodes.NETWORK_TIMEOUT;
    if (error.message.toLowerCase().includes('offline')) return ErrorCodes.NETWORK_OFFLINE;
    if (isNetworkError(error)) return ErrorCodes.NETWORK_ERROR;
  }
  return ErrorCodes.UNKNOWN_ERROR;
}

/**
 * Convert any error to an ApiError
 */
export function toApiError(error: unknown): ApiError {
  if (error instanceof Error) {
    return {
      message: error.message,
      code: getErrorCode(error),
    };
  }

  if (typeof error === 'string') {
    return {
      message: error,
      code: ErrorCodes.UNKNOWN_ERROR,
    };
  }

  return {
    message: 'An unknown error occurred',
    code: ErrorCodes.UNKNOWN_ERROR,
  };
}

// ==================== Exports ====================

export type { CircuitBreakerConfig, CircuitBreakerState, CircuitState };