/**
 * Request Helper Module
 *
 * Provides request timeout, automatic retry with exponential backoff,
 * and request cancellation support for API clients.
 *
 * @module lib/request-helper
 */

import { createLogger } from './logger';

const log = createLogger('RequestHelper');

// === Configuration Types ===

export interface RequestConfig {
  /** Timeout in milliseconds, default 30000 */
  timeout?: number;
  /** Number of retry attempts, default 3 */
  retries?: number;
  /** Base retry delay in milliseconds, default 1000 (exponential backoff applied) */
  retryDelay?: number;
  /** HTTP status codes that trigger retry, default [408, 429, 500, 502, 503, 504] */
  retryOn?: number[];
  /** Maximum retry delay cap in milliseconds, default 30000 */
  maxRetryDelay?: number;
}

export const DEFAULT_REQUEST_CONFIG: Required<RequestConfig> = {
  timeout: 30000,
  retries: 3,
  retryDelay: 1000,
  retryOn: [408, 429, 500, 502, 503, 504],
  maxRetryDelay: 30000,
};

// === Error Types ===

export class RequestError extends Error {
  constructor(
    message: string,
    public readonly status: number,
    public readonly statusText: string,
    public readonly responseBody?: string
  ) {
    super(message);
    this.name = 'RequestError';
  }

  /** Check if error is retryable based on status code */
  isRetryable(retryCodes: number[] = DEFAULT_REQUEST_CONFIG.retryOn): boolean {
    return retryCodes.includes(this.status);
  }

  /** Check if error is a timeout */
  isTimeout(): boolean {
    return this.status === 408 || this.message.includes('timeout');
  }

  /** Check if error is an authentication error (should NOT retry) */
  isAuthError(): boolean {
    return this.status === 401 || this.status === 403;
  }
}

export class RequestCancelledError extends Error {
  constructor(message: string = 'Request cancelled') {
    super(message);
    this.name = 'RequestCancelledError';
  }
}

// === Helper Functions ===

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

/**
 * Calculate exponential backoff delay with jitter
 * @param baseDelay Base delay in ms
 * @param attempt Current attempt number (0-indexed)
 * @param maxDelay Maximum delay cap
 * @returns Delay in milliseconds
 */
function calculateBackoff(
  baseDelay: number,
  attempt: number,
  maxDelay: number = DEFAULT_REQUEST_CONFIG.maxRetryDelay
): number {
  // Exponential backoff: baseDelay * 2^attempt
  const exponentialDelay = baseDelay * Math.pow(2, attempt);
  // Cap at maxDelay
  const cappedDelay = Math.min(exponentialDelay, maxDelay);
  // Add jitter (0-25% of delay) to prevent thundering herd
  const jitter = cappedDelay * 0.25 * Math.random();
  return Math.floor(cappedDelay + jitter);
}

// === Request with Retry ===

export interface RequestWithRetryOptions extends RequestInit {
  /** Request configuration for timeout and retry */
  config?: RequestConfig;
}

/**
 * Execute a fetch request with timeout and automatic retry support.
 *
 * Features:
 * - Configurable timeout with AbortController
 * - Automatic retry with exponential backoff
 * - Configurable retry status codes
 * - Jitter to prevent thundering herd
 *
 * @param url Request URL
 * @param options Fetch options + request config
 * @param config Request configuration (timeout, retries, etc.)
 * @returns Promise<Response>
 * @throws RequestError on failure after all retries exhausted
 * @throws RequestCancelledError if request was cancelled
 */
export async function requestWithRetry(
  url: string,
  options: RequestInit = {},
  config: RequestConfig = {}
): Promise<Response> {
  const {
    timeout = DEFAULT_REQUEST_CONFIG.timeout,
    retries = DEFAULT_REQUEST_CONFIG.retries,
    retryDelay = DEFAULT_REQUEST_CONFIG.retryDelay,
    retryOn = DEFAULT_REQUEST_CONFIG.retryOn,
  } = config;

  let lastError: RequestError | null = null;
  let responseBody = '';

  for (let attempt = 0; attempt <= retries; attempt++) {
    const controller = new AbortController();
    const timeoutId = setTimeout(() => controller.abort(), timeout);

    try {
      const response = await fetch(url, {
        ...options,
        signal: controller.signal,
      });

      clearTimeout(timeoutId);

      if (!response.ok) {
        // Try to read response body for error details
        try {
          responseBody = await response.text();
        } catch (e) {
          log.debug('Failed to read response body', { error: e });
          responseBody = '';
        }

        const error = new RequestError(
          `Request failed: ${response.status} ${response.statusText}`,
          response.status,
          response.statusText,
          responseBody
        );

        // Check if we should retry
        if (retryOn.includes(response.status) && attempt < retries) {
          const backoff = calculateBackoff(retryDelay, attempt);
          log.warn(
            `Request failed (${response.status}), ` +
            `retrying in ${backoff}ms (attempt ${attempt + 1}/${retries})`
          );
          await delay(backoff);
          continue;
        }

        throw error;
      }

      // Success - return response
      return response;
    } catch (error) {
      clearTimeout(timeoutId);

      // Re-throw RequestError (already formatted)
      if (error instanceof RequestError) {
        lastError = error;

        // Check if we should retry
        if (error.isRetryable(retryOn) && attempt < retries) {
          const backoff = calculateBackoff(retryDelay, attempt);
          log.warn(
            `Request error (${error.status}), ` +
            `retrying in ${backoff}ms (attempt ${attempt + 1}/${retries})`
          );
          await delay(backoff);
          continue;
        }

        throw error;
      }

      // Handle AbortError (timeout)
      if (error instanceof Error && error.name === 'AbortError') {
        const timeoutError = new RequestError(
          `Request timeout after ${timeout}ms`,
          408,
          'Request Timeout'
        );

        // Retry on timeout
        if (attempt < retries) {
          const backoff = calculateBackoff(retryDelay, attempt);
          log.warn(
            `Request timed out, ` +
            `retrying in ${backoff}ms (attempt ${attempt + 1}/${retries})`
          );
          await delay(backoff);
          lastError = timeoutError;
          continue;
        }

        throw timeoutError;
      }

      // Handle cancellation
      if (error instanceof RequestCancelledError) {
        throw error;
      }

      // Unknown error - wrap and throw
      throw new RequestError(
        error instanceof Error ? error.message : 'Unknown error',
        0,
        'Unknown Error',
        error instanceof Error ? error.stack : String(error)
      );
    }
  }

  // All retries exhausted
  throw lastError || new RequestError('All retry attempts exhausted', 0, 'Retry Exhausted');
}

/**
 * Execute a request and parse JSON response.
 * Combines requestWithRetry with JSON parsing.
 *
 * @param url Request URL
 * @param options Fetch options
 * @param config Request configuration
 * @returns Parsed JSON response
 */
export async function requestJson<T = unknown>(
  url: string,
  options: RequestInit = {},
  config: RequestConfig = {}
): Promise<T> {
  const response = await requestWithRetry(url, options, config);

  try {
    return await response.json();
  } catch (error) {
    throw new RequestError(
      `Failed to parse JSON response: ${error instanceof Error ? error.message : 'Unknown error'}`,
      0,
      'Parse Error',
      await response.text().catch(() => '')
    );
  }
}

// === Request Manager (Cancellation Support) ===

/**
 * Manages multiple concurrent requests with cancellation support.
 * Provides centralized control over request lifecycle.
 */
export class RequestManager {
  private controllers = new Map<string, AbortController>();
  private requestConfigs = new Map<string, RequestConfig>();

  /**
   * Create a new request with an ID for tracking.
   * Returns the AbortController for signal attachment.
   *
   * @param id Unique request identifier
   * @param config Optional request configuration
   * @returns AbortController for the request
   */
  createRequest(id: string, config?: RequestConfig): AbortController {
    // Cancel existing request with same ID
    if (this.controllers.has(id)) {
      this.cancelRequest(id);
    }

    const controller = new AbortController();
    this.controllers.set(id, controller);
    if (config) {
      this.requestConfigs.set(id, config);
    }

    return controller;
  }

  /**
   * Execute a managed request with automatic tracking.
   * The request will be automatically removed when complete.
   *
   * @param id Unique request identifier
   * @param url Request URL
   * @param options Fetch options
   * @param config Request configuration
   * @returns Response promise
   */
  async executeManaged(
    id: string,
    url: string,
    options: RequestInit = {},
    config: RequestConfig = {}
  ): Promise<Response> {
    const controller = this.createRequest(id, config);

    try {
      const response = await requestWithRetry(
        url,
        {
          ...options,
          signal: controller.signal,
        },
        config
      );

      // Clean up on success
      this.controllers.delete(id);
      this.requestConfigs.delete(id);

      return response;
    } catch (error) {
      // Clean up on error
      this.controllers.delete(id);
      this.requestConfigs.delete(id);

      throw error;
    }
  }

  /**
   * Execute a managed JSON request with automatic tracking.
   *
   * @param id Unique request identifier
   * @param url Request URL
   * @param options Fetch options
   * @param config Request configuration
   * @returns Parsed JSON response
   */
  async executeManagedJson<T = unknown>(
    id: string,
    url: string,
    options: RequestInit = {},
    config: RequestConfig = {}
  ): Promise<T> {
    const response = await this.executeManaged(id, url, options, config);

    try {
      return await response.json();
    } catch (error) {
      throw new RequestError(
        `Failed to parse JSON response: ${error instanceof Error ? error.message : 'Unknown error'}`,
        0,
        'Parse Error',
        await response.text().catch(() => '')
      );
    }
  }

  /**
   * Cancel a specific request by ID.
   *
   * @param id Request identifier
   * @returns true if request was cancelled, false if not found
   */
  cancelRequest(id: string): boolean {
    const controller = this.controllers.get(id);
    if (controller) {
      controller.abort();
      this.controllers.delete(id);
      this.requestConfigs.delete(id);
      return true;
    }
    return false;
  }

  /**
   * Check if a request is currently in progress.
   *
   * @param id Request identifier
   * @returns true if request is active
   */
  isRequestActive(id: string): boolean {
    return this.controllers.has(id);
  }

  /**
   * Get all active request IDs.
   *
   * @returns Array of active request IDs
   */
  getActiveRequestIds(): string[] {
    return Array.from(this.controllers.keys());
  }

  /**
   * Cancel all active requests.
   */
  cancelAll(): void {
    this.controllers.forEach((controller, id) => {
      controller.abort();
      log.debug(`Cancelled request: ${id}`);
    });
    this.controllers.clear();
    this.requestConfigs.clear();
  }

  /**
   * Get the number of active requests.
   */
  get activeCount(): number {
    return this.controllers.size;
  }
}

// === Default Request Manager Instance ===

/**
 * Global request manager instance for application-wide request tracking.
 * Use this for simple cases; create new instances for isolated contexts.
 */
export const globalRequestManager = new RequestManager();

// === Convenience Functions ===

/**
 * Create a GET request with retry support.
 */
export async function get(
  url: string,
  headers?: HeadersInit,
  config?: RequestConfig
): Promise<Response> {
  return requestWithRetry(url, { method: 'GET', headers }, config);
}

/**
 * Create a POST request with retry support.
 */
export async function post(
  url: string,
  body?: unknown,
  headers?: HeadersInit,
  config?: RequestConfig
): Promise<Response> {
  return requestWithRetry(
    url,
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        ...headers,
      },
      body: body ? JSON.stringify(body) : undefined,
    },
    config
  );
}

/**
 * Create a PUT request with retry support.
 */
export async function put(
  url: string,
  body?: unknown,
  headers?: HeadersInit,
  config?: RequestConfig
): Promise<Response> {
  return requestWithRetry(
    url,
    {
      method: 'PUT',
      headers: {
        'Content-Type': 'application/json',
        ...headers,
      },
      body: body ? JSON.stringify(body) : undefined,
    },
    config
  );
}

/**
 * Create a DELETE request with retry support.
 */
export async function del(
  url: string,
  headers?: HeadersInit,
  config?: RequestConfig
): Promise<Response> {
  return requestWithRetry(url, { method: 'DELETE', headers }, config);
}

/**
 * Create a PATCH request with retry support.
 */
export async function patch(
  url: string,
  body?: unknown,
  headers?: HeadersInit,
  config?: RequestConfig
): Promise<Response> {
  return requestWithRetry(
    url,
    {
      method: 'PATCH',
      headers: {
        'Content-Type': 'application/json',
        ...headers,
      },
      body: body ? JSON.stringify(body) : undefined,
    },
    config
  );
}

export default {
  requestWithRetry,
  requestJson,
  RequestManager,
  globalRequestManager,
  RequestError,
  RequestCancelledError,
  get,
  post,
  put,
  del,
  patch,
  DEFAULT_REQUEST_CONFIG,
};