feat(api-gateway): scaffold gateway foundation and request routing architecture

Author: rabsqueen

src/gateway/gateway.controller.ts

@@ -0,0 +1,40 @@
+import {
+  All,
+  Body,
+  Controller,
+  Headers,
+  HttpCode,
+  Param,
+  Query,
+  Req,
+} from '@nestjs/common';
+import { Request } from 'express';
+
+import { GatewayService } from './gateway.service';
+
+@Controller()
+export class GatewayController {
+  constructor(
+    private readonly gatewayService: GatewayService,
+  ) {}
+
+  @All(':service/*path')
+  @HttpCode(200)
+  async proxyRequest(
+    @Param('service') service: string,
+    @Param('path') path: string,
+    @Req() request: Request,
+    @Body() body: unknown,
+    @Query() query: Record<string, unknown>,
+    @Headers() headers: Record<string, string>,
+  ) {
+    return this.gatewayService.forwardRequest({
+      service,
+      path,
+      method: request.method,
+      body,
+      query,
+      headers,
+    });
+  }
+}

src/gateway/gateway.module.ts

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+import { Module } from '@nestjs/common';
+
+import { GatewayController } from './gateway.controller';
+import { GatewayService } from './gateway.service';
+import { RouterService } from './router/router.service';
+import { RouteResolver } from './router/route-resolver';
+
+@Module({
+  controllers: [GatewayController],
+  providers: [GatewayService, RouterService, RouteResolver],
+  exports: [GatewayService, RouterService],
+})
+export class GatewayModule {}

src/gateway/gateway.service.ts

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+import {
+  Injectable,
+  NotFoundException,
+} from '@nestjs/common';
+
+import { RouterService } from './router/router.service';
+
+export interface GatewayRequest {
+  service: string;
+  path: string;
+  method: string;
+  body?: unknown;
+  query?: Record<string, unknown>;
+  headers?: Record<string, string>;
+}
+
+@Injectable()
+export class GatewayService {
+  constructor(
+    private readonly routerService: RouterService,
+  ) {}
+
+  async forwardRequest(
+    request: GatewayRequest,
+  ): Promise<unknown> {
+    const destination =
+      this.routerService.resolveService(
+        request.service,
+      );
+
+    if (!destination) {
+      throw new NotFoundException(
+        `Unknown service: ${request.service}`,
+      );
+    }
+
+    return this.routerService.forward(
+      destination,
+      request,
+    );
+  }
+}

src/gateway/middleware/logging.middleware.ts

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+import {
+  Injectable,
+  NotFoundException,
+} from '@nestjs/common';
+
+import {
+  SERVICE_REGISTRY,
+  ServiceDefinition,
+} from './service-registry';
+
+@Injectable()
+export class RouteResolver {
+  resolve(
+    service: string,
+  ): ServiceDefinition {
+    const definition =
+      SERVICE_REGISTRY[service];
+
+    if (!definition || !definition.enabled) {
+      throw new NotFoundException(
+        `Service "${service}" is unavailable.`,
+      );
+    }
+
+    return definition;
+  }
+}

src/gateway/middleware/rate-limit.middleware.ts

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+import { Injectable } from '@nestjs/common';
+
+import {
+  ServiceDefinition,
+} from './service-registry';
+import { RouteResolver } from './route-resolver';
+import {
+  GatewayRequest,
+} from '../gateway.service';
+
+@Injectable()
+export class RouterService {
+  constructor(
+    private readonly routeResolver: RouteResolver,
+  ) {}
+
+  resolveService(
+    service: string,
+  ): ServiceDefinition {
+    return this.routeResolver.resolve(
+      service,
+    );
+  }
+
+  async forward(
+    destination: ServiceDefinition,
+    request: GatewayRequest,
+  ): Promise<unknown> {
+    /**
+     * Phase 2 will replace this with:
+     * - Authentication
+     * - Correlation IDs
+     * - Circuit Breaker
+     * - Request Transformation
+     * - Native fetch/HTTP forwarding
+     */
+
+    return {
+      gateway: true,
+      service: destination.name,
+      destination:
+        destination.baseUrl,
+      method: request.method,
+      path: request.path,
+      query: request.query,
+      body: request.body,
+      status: 'Request routing scaffolded',
+    };
+  }
+}

src/gateway/router/route-resolver.ts

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+export interface ServiceDefinition {
+  name: string;
+  baseUrl: string;
+  timeout: number;
+  enabled: boolean;
+}
+
+export const SERVICE_REGISTRY: Record<
+  string,
+  ServiceDefinition
+> = {
+  auth: {
+    name: 'Authentication Service',
+    baseUrl:
+      process.env.AUTH_SERVICE_URL ??
+      'http://localhost:3001',
+    timeout: 5000,
+    enabled: true,
+  },
+
+  quest: {
+    name: 'Quest Service',
+    baseUrl:
+      process.env.QUEST_SERVICE_URL ??
+      'http://localhost:3002',
+    timeout: 5000,
+    enabled: true,
+  },
+
+  analytics: {
+    name: 'Analytics Service',
+    baseUrl:
+      process.env.ANALYTICS_SERVICE_URL ??
+      'http://localhost:3003',
+    timeout: 5000,
+    enabled: true,
+  },
+};