Response Time

import { Request, Response, NextFunction, RequestHandler } from 'express';

/**
 * Response time options
 */
interface ResponseTimeOptions {
  /** Header name (default: X-Response-Time) */
  header?: string;
  /** Include unit suffix (default: true, e.g., "12.34ms") */
  suffix?: boolean;
  /** Number of decimal places (default: 2) */
  digits?: number;
  /** Enable console logging (default: false in production) */
  log?: boolean;
  /** Log slow requests above this threshold in ms (default: 1000) */
  slowThreshold?: number;
}

/**
 * Response time middleware
 * - Adds X-Response-Time header (high precision using hrtime)
 * - Optional request/response logging
 * - Slow request warnings
 */
export const responseTime = (options: ResponseTimeOptions = {}): RequestHandler => {
  const {
    header = 'X-Response-Time',
    suffix = true,
    digits = 2,
    log = process.env.NODE_ENV !== 'production',
    slowThreshold = 1000,
  } = options;

  return (req: Request, res: Response, next: NextFunction) => {
    const start = process.hrtime.bigint();
    const ip = req.ip || req.socket?.remoteAddress || 'unknown';

    // Log incoming request (only in dev or if explicitly enabled)
    if (log) {
      console.log(
        `[REQ] [${new Date().toISOString()}] ${req.method} ${req.originalUrl} - IP: ${ip}`
      );
    }

    res.on('finish', () => {
      const end = process.hrtime.bigint();
      const durationNs = Number(end - start);
      const durationMs = durationNs / 1_000_000;

      const value = suffix
        ? `${durationMs.toFixed(digits)}ms`
        : durationMs.toFixed(digits);

      // Set header if not already sent
      if (!res.headersSent) {
        res.setHeader(header, value);
      }

      // Log response (only in dev or if explicitly enabled)
      if (log) {
        console.log(
          `[RES] [${new Date().toISOString()}] ${req.method} ${req.originalUrl} - ${res.statusCode} - ${value}`
        );
      }

      // Always warn about slow requests (even in production)
      if (durationMs > slowThreshold) {
        console.warn(
          `Slow request: ${req.method} ${req.originalUrl} took ${value}`
        );
      }
    });

    next();
  };
};

/**
 * Default middleware - headers only, no logging in production
 */
export const defaultResponseTime: RequestHandler = responseTime();

/**
 * Development middleware - with full logging
 */
export const devResponseTime: RequestHandler = responseTime({ log: true });

/**
 * Production middleware - headers only, no logging
 */
export const prodResponseTime: RequestHandler = responseTime({ log: false });

/**
 * Server Timing API support
 * Adds Server-Timing header for detailed performance metrics
 * Visible in browser DevTools Network tab
 */
export const serverTiming = (): RequestHandler => {
  return (req: Request, res: Response, next: NextFunction) => {
    const start = process.hrtime.bigint();
    const timings: string[] = [];

    // Attach method to add custom timings
    (res as any).timing = (name: string, duration: number, desc?: string) => {
      timings.push(desc ? `${name};dur=${duration};desc="${desc}"` : `${name};dur=${duration}`);
    };

    res.on('finish', () => {
      const totalMs = Number(process.hrtime.bigint() - start) / 1_000_000;
      timings.unshift(`total;dur=${totalMs.toFixed(2)};desc="Total"`);

      if (!res.headersSent) {
        res.setHeader('Server-Timing', timings.join(', '));
      }
    });

    next();
  };
};