Add HealthService to perform health checks on payment processors

src/modules/health/services/health.service.ts

@@ -0,0 +1,87 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { HttpService } from '@nestjs/axios';
+import { ConfigService } from '@nestjs/config';
+import { Cron } from '@nestjs/schedule';
+import { firstValueFrom } from 'rxjs';
+import { ServiceStatusEnum } from '../enumns/service-status.enum';
+import { ProcessorTypeEnum } from '../../payments/enumns/processor-type.enum';
+
+@Injectable()
+export class HealthService {
+  private readonly logger = new Logger(HealthService.name);
+  private defaultServiceStatus: ServiceStatusEnum = ServiceStatusEnum.UP;
+  private fallbackServiceStatus: ServiceStatusEnum = ServiceStatusEnum.UP;
+
+  constructor(
+    private readonly httpService: HttpService,
+    private readonly configService: ConfigService,
+  ) {}
+
+  @Cron('*/5 * * * * *')
+  async performHealthChecks() {
+    const defaultUrl: string =
+      this.configService.get<string>('paymentProcessors.defaultUrl') ?? '';
+    const fallbackUrl: string =
+      this.configService.get<string>('paymentProcessors.fallbackUrl') ?? '';
+
+    await Promise.all([
+      this.checkServiceHealth(
+        ProcessorTypeEnum.DEFAULT,
+        `${defaultUrl}/payments/service-health`,
+      ),
+      this.checkServiceHealth(
+        ProcessorTypeEnum.FALLBACK,
+        `${fallbackUrl}/payments/service-health`,
+      ),
+    ]);
+  }
+
+  shouldUseDefaultProcessor(): boolean {
+    return this.defaultServiceStatus === ServiceStatusEnum.UP;
+  }
+
+  shouldUseFallbackProcessor(): boolean {
+    return this.fallbackServiceStatus === ServiceStatusEnum.UP;
+  }
+
+  getPreferredProcessor(): 'default' | 'fallback' | null {
+    if (this.shouldUseDefaultProcessor()) {
+      return 'default';
+    } else if (this.shouldUseFallbackProcessor()) {
+      return 'fallback';
+    }
+    return null;
+  }
+
+  private async checkServiceHealth(
+    serviceName: string,
+    url: string,
+  ): Promise<void> {
+    let status: ServiceStatusEnum;
+
+    try {
+      const response = await firstValueFrom(
+        this.httpService.get(url, {
+          timeout: 6000,
+        }),
+      );
+
+      status =
+        response.status === 200 ? ServiceStatusEnum.UP : ServiceStatusEnum.DOWN;
+
+      this.logger.log(`Health check for ${serviceName}: ${status}`);
+    } catch (error) {
+      status = ServiceStatusEnum.DOWN;
+
+      this.logger.warn(
+        `Health check failed for ${serviceName}: ${error.message}`,
+      );
+    }
+
+    if (serviceName === 'default') {
+      this.defaultServiceStatus = status;
+    } else {
+      this.fallbackServiceStatus = status;
+    }
+  }
+}