/*
 * Copyright 2019 gRPC authors.
 *
 * 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 { log } from './logging';
import { LogVerbosity } from './constants';
import { getDefaultAuthority } from './resolver';
import { Socket } from 'net';
import * as http from 'http';
import * as tls from 'tls';
import * as logging from './logging';
import {
  SubchannelAddress,
  isTcpSubchannelAddress,
  subchannelAddressToString,
} from './subchannel-address';
import { ChannelOptions } from './channel-options';
import { GrpcUri, parseUri, splitHostPort, uriToString } from './uri-parser';
import { URL } from 'url';

const TRACER_NAME = 'proxy';

function trace(text: string): void {
  logging.trace(LogVerbosity.DEBUG, TRACER_NAME, text);
}

interface ProxyInfo {
  address?: string;
  creds?: string;
}

function getProxyInfo(): ProxyInfo {
  let proxyEnv = '';
  let envVar = '';
  /* Prefer using 'grpc_proxy'. Fallback on 'http_proxy' if it is not set.
   * Also prefer using 'https_proxy' with fallback on 'http_proxy'. The
   * fallback behavior can be removed if there's a demand for it.
   */
  if (process.env.grpc_proxy) {
    envVar = 'grpc_proxy';
    proxyEnv = process.env.grpc_proxy;
  } else if (process.env.https_proxy) {
    envVar = 'https_proxy';
    proxyEnv = process.env.https_proxy;
  } else if (process.env.http_proxy) {
    envVar = 'http_proxy';
    proxyEnv = process.env.http_proxy;
  } else {
    return {};
  }
  let proxyUrl: URL;
  try {
    proxyUrl = new URL(proxyEnv);
  } catch (e) {
    log(LogVerbosity.ERROR, `cannot parse value of "${envVar}" env var`);
    return {};
  }
  if (proxyUrl.protocol !== 'http:') {
    log(
      LogVerbosity.ERROR,
      `"${proxyUrl.protocol}" scheme not supported in proxy URI`
    );
    return {};
  }
  let userCred: string | null = null;
  if (proxyUrl.username) {
    if (proxyUrl.password) {
      log(LogVerbosity.INFO, 'userinfo found in proxy URI');
      userCred = `${proxyUrl.username}:${proxyUrl.password}`;
    } else {
      userCred = proxyUrl.username;
    }
  }
  const hostname = proxyUrl.hostname;
  let port = proxyUrl.port;
  /* The proxy URL uses the scheme "http:", which has a default port number of
   * 80. We need to set that explicitly here if it is omitted because otherwise
   * it will use gRPC's default port 443. */
  if (port === '') {
    port = '80';
  }
  const result: ProxyInfo = {
    address: `${hostname}:${port}`,
  };
  if (userCred) {
    result.creds = userCred;
  }
  trace(
    'Proxy server ' + result.address + ' set by environment variable ' + envVar
  );
  return result;
}

function getNoProxyHostList(): string[] {
  /* Prefer using 'no_grpc_proxy'. Fallback on 'no_proxy' if it is not set. */
  let noProxyStr: string | undefined = process.env.no_grpc_proxy;
  let envVar = 'no_grpc_proxy';
  if (!noProxyStr) {
    noProxyStr = process.env.no_proxy;
    envVar = 'no_proxy';
  }
  if (noProxyStr) {
    trace('No proxy server list set by environment variable ' + envVar);
    return noProxyStr.split(',');
  } else {
    return [];
  }
}

export interface ProxyMapResult {
  target: GrpcUri;
  extraOptions: ChannelOptions;
}

export function mapProxyName(
  target: GrpcUri,
  options: ChannelOptions
): ProxyMapResult {
  const noProxyResult: ProxyMapResult = {
    target: target,
    extraOptions: {},
  };
  if ((options['grpc.enable_http_proxy'] ?? 1) === 0) {
    return noProxyResult;
  }
  if (target.scheme === 'unix') {
    return noProxyResult;
  }
  const proxyInfo = getProxyInfo();
  if (!proxyInfo.address) {
    return noProxyResult;
  }
  const hostPort = splitHostPort(target.path);
  if (!hostPort) {
    return noProxyResult;
  }
  const serverHost = hostPort.host;
  for (const host of getNoProxyHostList()) {
    if (host === serverHost) {
      trace(
        'Not using proxy for target in no_proxy list: ' + uriToString(target)
      );
      return noProxyResult;
    }
  }
  const extraOptions: ChannelOptions = {
    'grpc.http_connect_target': uriToString(target),
  };
  if (proxyInfo.creds) {
    extraOptions['grpc.http_connect_creds'] = proxyInfo.creds;
  }
  return {
    target: {
      scheme: 'dns',
      path: proxyInfo.address,
    },
    extraOptions: extraOptions,
  };
}

export interface ProxyConnectionResult {
  socket?: Socket;
  realTarget?: GrpcUri;
}

export function getProxiedConnection(
  address: SubchannelAddress,
  channelOptions: ChannelOptions,
  connectionOptions: tls.ConnectionOptions
): Promise<ProxyConnectionResult> {
  if (!('grpc.http_connect_target' in channelOptions)) {
    return Promise.resolve<ProxyConnectionResult>({});
  }
  const realTarget = channelOptions['grpc.http_connect_target'] as string;
  const parsedTarget = parseUri(realTarget);
  if (parsedTarget === null) {
    return Promise.resolve<ProxyConnectionResult>({});
  }
  const options: http.RequestOptions = {
    method: 'CONNECT',
    path: parsedTarget.path,
  };
  const headers: http.OutgoingHttpHeaders = {
    Host: parsedTarget.path,
  };
  // Connect to the subchannel address as a proxy
  if (isTcpSubchannelAddress(address)) {
    options.host = address.host;
    options.port = address.port;
  } else {
    options.socketPath = address.path;
  }
  if ('grpc.http_connect_creds' in channelOptions) {
    headers['Proxy-Authorization'] =
      'Basic ' +
      Buffer.from(
        channelOptions['grpc.http_connect_creds'] as string
      ).toString('base64');
  }
  options.headers = headers
  const proxyAddressString = subchannelAddressToString(address);
  trace('Using proxy ' + proxyAddressString + ' to connect to ' + options.path);
  return new Promise<ProxyConnectionResult>((resolve, reject) => {
    const request = http.request(options);
    request.once('connect', (res, socket, head) => {
      request.removeAllListeners();
      socket.removeAllListeners();
      if (res.statusCode === 200) {
        trace(
          'Successfully connected to ' +
            options.path +
            ' through proxy ' +
            proxyAddressString
        );
        if ('secureContext' in connectionOptions) {
          /* The proxy is connecting to a TLS server, so upgrade this socket
           * connection to a TLS connection.
           * This is a workaround for https://github.com/nodejs/node/issues/32922
           * See https://github.com/grpc/grpc-node/pull/1369 for more info. */
          const targetPath = getDefaultAuthority(parsedTarget);
          const hostPort = splitHostPort(targetPath);
          const remoteHost = hostPort?.host ?? targetPath;

          const cts = tls.connect(
            {
              host: remoteHost,
              servername: remoteHost,
              socket: socket,
              ...connectionOptions,
            },
            () => {
              trace(
                'Successfully established a TLS connection to ' +
                  options.path +
                  ' through proxy ' +
                  proxyAddressString
              );
              resolve({ socket: cts, realTarget: parsedTarget });
            }
          );
          cts.on('error', (error: Error) => {
            trace('Failed to establish a TLS connection to ' +
                    options.path +
                    ' through proxy ' +
                    proxyAddressString +
                    ' with error ' +
                    error.message);
            reject();
          });
        } else {
          trace(
            'Successfully established a plaintext connection to ' +
              options.path +
              ' through proxy ' +
              proxyAddressString
          );
          resolve({
            socket,
            realTarget: parsedTarget,
          });
        }
      } else {
        log(
          LogVerbosity.ERROR,
          'Failed to connect to ' +
            options.path +
            ' through proxy ' +
            proxyAddressString +
            ' with status ' +
            res.statusCode
        );
        reject();
      }
    });
    request.once('error', (err) => {
      request.removeAllListeners();
      log(
        LogVerbosity.ERROR,
        'Failed to connect to proxy ' +
          proxyAddressString +
          ' with error ' +
          err.message
      );
      reject();
    });
    request.end();
  });
}