import * as grpc from 'grpc';
import * as prom from 'prom-client';

const grpcHistogram = new prom.Histogram({
  name: 'grpc_requests_seconds',
  help: 'measures grpc request duration',
  labelNames: ['status', 'service', 'method'],
  buckets: [0.2, 0.5, 1, 1.5, 3, 5, 10],
});

/**
 *
 * @param options
 * @param nextCall
 */
export const prometheusInterceptor = (options: grpc.CallOptions, nextCall: Function): grpc.InterceptingCall => {
  return new grpc.InterceptingCall(nextCall(options), {
    start(metadata, listener, next): void {

      const [service, method] = options.method_definition.path.split('/').splice(1, 2);

      const labels = {
        status: grpc.status[grpc.status.UNKNOWN],
        service,
        method,
      };

      const timeRequest = grpcHistogram.startTimer(labels);

      const newListener = {
        onReceiveStatus(status: grpc.StatusObject, nextStatus: Function): void {
          labels.status = grpc.status[status.code];
          timeRequest();
          nextStatus(status);
        },
      };
      next(metadata, newListener);
    },
  });
};