import { CallHandler, ExecutionContext, Injectable, NestInterceptor } from '@nestjs/common';
import type { Observable } from 'rxjs';
import { finalize } from 'rxjs/operators';
import { MetricsService } from './metrics.service';

type RequestLike = { method?: string; baseUrl?: string; route?: { path?: string } };
type ResponseLike = { statusCode?: number };

@Injectable()
export class MetricsInterceptor implements NestInterceptor {
  constructor(private readonly metrics: MetricsService) {}

  intercept(context: ExecutionContext, next: CallHandler): Observable<unknown> {
    if (context.getType() !== 'http') return next.handle();
    const http = context.switchToHttp();
    const request = http.getRequest<RequestLike>();
    const response = http.getResponse<ResponseLike>();
    const startedAt = this.metrics.beginRequest();
    return next.handle().pipe(finalize(() => {
      const route = `${request.baseUrl ?? ''}${request.route?.path ?? '/unmatched'}`;
      this.metrics.finishRequest(startedAt, request.method ?? 'UNKNOWN', route, response.statusCode ?? 500);
    }));
  }
}