text: #include <math.h>
  #include <uWS/uWS.h>
  
  #include <iostream>
  #include <string>
  
  #include "json.hpp"
  #include "vehicle_controller.h"
  
  // for convenience
  using nlohmann::json;
  using std::string;
  
  // For converting back and forth between radians and degrees.
  constexpr double pi() { return M_PI; }
  double deg2rad(double x) { return x * pi() / 180; }
  double rad2deg(double x) { return x * 180 / pi(); }
  
  // Checks if the SocketIO event has JSON data.
  // If there is data the JSON object in string format will be returned,
  // else the empty string "" will be returned.
  string hasData(string s) {
    auto found_null = s.find("null");
    auto b1 = s.find_first_of("[");
    auto b2 = s.find_last_of("]");
    if (found_null != string::npos) {
      return "";
    } else if (b1 != string::npos && b2 != string::npos) {
      return s.substr(b1, b2 - b1 + 1);
    }
    return "";
  }
  
  int main() {
    uWS::Hub h;
  
    VehicleController controller;
  
    h.onMessage([&controller](uWS::WebSocket<uWS::SERVER> ws, char *data,
                              size_t length, uWS::OpCode opCode) {
      // "42" at the start of the message means there's a websocket message
      // event. The 4 signifies a websocket message The 2 signifies a
      // websocket event
      if (length && length > 2 && data[0] == '4' && data[1] == '2') {
        auto s = hasData(string(data).substr(0, length));
  
        if (s != "") {
          auto j = json::parse(s);
  
          string event = j[0].get<string>();
  
          if (event == "telemetry") {
            // j[1] is the data JSON object
            double cte = std::stod(j[1]["cte"].get<string>());
            double speed = std::stod(j[1]["speed"].get<string>());
            // double angle = std::stod(j[1]["steering_angle"].get<string>());
  
            controller.setCrossTrackError(cte);
            controller.setTelemetrySpeed(speed);
            controller.step();
  
            float steering_action = controller.getActionSteeringAngle();
            float throttle_action = controller.getActionThrottle();
  
            std::cout << "[telemetry] cte: " << cte << ", speed_mph: " << speed
                      << std::endl
                      << "[action]: steering: " << steering_action
                      << ", throttle: " << throttle_action << std::endl;
  
            json msgJson;
            msgJson["steering_angle"] = steering_action;
            msgJson["throttle"] = throttle_action;
            auto msg = "42[\"steer\"," + msgJson.dump() + "]";
            ws.send(msg.data(), msg.length(), uWS::OpCode::TEXT);
          }  // end "telemetry" if
        } else {
          // Manual driving
          string msg = "42[\"manual\",{}]";
          ws.send(msg.data(), msg.length(), uWS::OpCode::TEXT);
        }
      }  // end websocket message if
    });  // end h.onMessage
  
    h.onConnection([&h](uWS::WebSocket<uWS::SERVER> ws, uWS::HttpRequest req) {
      std::cout << "Connected!!!" << std::endl;
    });
  
    h.onDisconnection([&h](uWS::WebSocket<uWS::SERVER> ws, int code,
                           char *message, size_t length) {
      ws.close();
      std::cout << "Disconnected" << std::endl;
    });
  
    int port = 4567;
    if (h.listen(port)) {
      std::cout << "Listening to port " << port << std::endl;
    } else {
      std::cerr << "Failed to listen to port" << std::endl;
      return -1;
    }
  
    h.run();
  }
  