import * as grpc from "grpc";

export enum InterceptorType {
  Unary,
  ClientStreaming,
  ServerStreaming,
  BidiStreaming,
}

type InterceptorFn =  (options: grpc.CallOptions, next: Function) => grpc.InterceptingCall;

export interface InterceptorChainConfig {
  type: InterceptorType;
  interceptorFn: InterceptorFn;
}

export type Interceptor = (methodDefinition: grpc.MethodDefinition<any, any>) => InterceptorFn;

/**
 * Interceptor chain, helps to chain together multiple interceptors
 * @param interceptors
 */
export function interceptorChain(interceptors: InterceptorChainConfig[]): Interceptor[] {
  return interceptors.map(i => {
    return (methodDefinition: grpc.MethodDefinition<any, any>): InterceptorFn => {
      switch (i.type) {
        case InterceptorType.Unary:
          if (!methodDefinition.requestStream && !methodDefinition.responseStream) {
            return i.interceptorFn;
          }
          break;
        case InterceptorType.ClientStreaming:
          if (methodDefinition.requestStream && !methodDefinition.responseStream) {
            return i.interceptorFn;
          }
          break;
        case InterceptorType.ServerStreaming:
          if (!methodDefinition.requestStream && methodDefinition.responseStream) {
            return i.interceptorFn;
          }
          break;
        case InterceptorType.BidiStreaming:
          if (methodDefinition.requestStream && methodDefinition.responseStream) {
            return i.interceptorFn;
          }
          break;
      }
      throw new Error(`interceptor type ${i.type} not supported.`);
    };
  });
}