Request ID

import { FastifyInstance, FastifyRequest, FastifyReply } from "fastify";
import crypto from "crypto";

/**
 * Request ID configuration
 */
interface RequestIdConfig {
  headerName?: string;
  prefix?: string;
  generator?: () => string;
}

const defaultConfig: RequestIdConfig = {
  headerName: "x-request-id",
  prefix: "req",
  generator: () => crypto.randomUUID(),
};

/**
 * Generate a unique request ID
 */
export function generateRequestId(prefix = "req"): string {
  return `${prefix}_${Date.now()}_${crypto.randomBytes(8).toString("hex")}`;
}

/**
 * Register request ID handling
 * - Uses incoming request ID if present
 * - Generates new ID if not
 * - Adds ID to response headers
 * - Adds ID to log context
 */
export function registerRequestId(
  app: FastifyInstance,
  config?: RequestIdConfig
): void {
  const { headerName, prefix, generator } = { ...defaultConfig, ...config };

  // Add request ID before routing
  app.addHook("onRequest", async (request: FastifyRequest, reply: FastifyReply) => {
    // Use existing ID from header or generate new one
    const existingId = request.headers[headerName!] as string | undefined;
    const requestId = existingId ?? generator!();

    // Store on request for access in handlers
    (request as any).requestId = requestId;

    // Add to response headers
    reply.header(headerName!, requestId);
    reply.header("x-correlation-id", requestId);
  });
}

/**
 * Get request ID from request object
 */
export function getRequestId(request: FastifyRequest): string {
  return (request as any).requestId ?? request.id;
}

/**
 * Create a correlation context for propagating request ID to downstream services
 */
export function createCorrelationHeaders(request: FastifyRequest): Record<string, string> {
  const requestId = getRequestId(request);
  return {
    "x-request-id": requestId,
    "x-correlation-id": requestId,
    "x-trace-id": requestId,
  };
}

/**
 * Middleware to require request ID (for services that should always receive one)
 */
export async function requireRequestId(
  request: FastifyRequest,
  reply: FastifyReply
): Promise<void> {
  const headerName = "x-request-id";
  const requestId = request.headers[headerName];

  if (!requestId) {
    reply.status(400).send({
      error: "Bad Request",
      message: `Missing required header: ${headerName}`,
    });
  }
}

// Usage:
// registerRequestId(app);
//
// In handlers:
// const requestId = getRequestId(request);
//
// For downstream calls:
// fetch(url, { headers: createCorrelationHeaders(request) });