/*
 * Copyright 2021 Lightbend Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import * as util from 'util';
import * as Protobuf from 'protobufjs';
import * as Grpc from '@grpc/grpc-js';
import { ServiceClientConstructor } from '@grpc/grpc-js/build/src/make-client';

export interface GrpcClient extends Grpc.Client {
  [methodName: string]: Function;
}

export interface GrpcClientCreator {
  createClient(
    address: string,
    credentials?: Grpc.ChannelCredentials,
  ): GrpcClient;
}

export interface GrpcClientLookup {
  [index: string]: GrpcClientLookup | GrpcClientCreator;
}

export class GrpcUtil {
  /**
   * Create gRPC client creators for defined services, with promisified clients.
   */
  static clientCreators(
    namespace: Protobuf.Namespace,
    grpc: Grpc.GrpcObject,
  ): GrpcClientLookup {
    const result: GrpcClientLookup = {};
    for (const serviceFqn of GrpcUtil.getServiceNames(namespace)) {
      let currentLookup = result;
      let currentGrpc = grpc;
      const nameComponents = serviceFqn.split('.');
      for (const packageName of nameComponents.slice(0, -1)) {
        if (!currentLookup[packageName]) {
          currentLookup[packageName] = {};
        }
        currentLookup = currentLookup[packageName] as GrpcClientLookup;
        currentGrpc = currentGrpc[packageName] as Grpc.GrpcObject;
      }
      const serviceName = nameComponents[nameComponents.length - 1];
      const serviceClientConstructor = currentGrpc[
        serviceName
      ] as ServiceClientConstructor;
      const clientCreator = function (
        address: string,
        credentials?: Grpc.ChannelCredentials,
      ) {
        const creds = credentials || Grpc.credentials.createInsecure();
        const client = new serviceClientConstructor(address, creds);
        return GrpcUtil.promisifyClient(client);
      };
      currentLookup[serviceName] = {
        createClient: clientCreator,
      };
    }
    return result;
  }

  /**
   * Iterate through a (resolved) protobufjs reflection object to find services.
   */
  static getServiceNames(
    obj: Protobuf.ReflectionObject,
    parentName: string = '',
  ): Array<string> {
    const fullName = parentName === '' ? obj.name : parentName + '.' + obj.name;
    if (obj instanceof Protobuf.Service) {
      return [fullName];
    } else if (
      obj instanceof Protobuf.Namespace &&
      typeof obj.nestedArray !== 'undefined'
    ) {
      return obj.nestedArray
        .map((nestedObj) => GrpcUtil.getServiceNames(nestedObj, fullName))
        .reduce((acc, val) => acc.concat(val), []);
    }
    return [];
  }

  /**
   * add async versions of unary request methods, suffixed with the given suffix
   */
  static promisifyClient(client: any, suffix: String = '') {
    Object.keys(Object.getPrototypeOf(client)).forEach((methodName) => {
      const methodFunction = client[methodName];
      if (
        methodFunction.requestStream == false &&
        methodFunction.responseStream == false
      ) {
        client[methodName + suffix] = util
          .promisify(methodFunction)
          .bind(client);
      }
    });
    return client;
  }
}