text: #include <uWS/uWS.h>
  #include <iostream>
  #include "json.hpp"
  #include "PID.h"
  #include <math.h>
  
  // for convenience
  using json = nlohmann::json;
  
  // 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.
  std::string hasData(std::string s) {
    auto found_null = s.find("null");
    auto b1 = s.find_first_of("[");
    auto b2 = s.find_last_of("]");
    if (found_null != std::string::npos) {
      return "";
    }
    else if (b1 != std::string::npos && b2 != std::string::npos) {
      return s.substr(b1, b2 - b1 + 1);
    }
    return "";
  }
  
  int main()
  {
    uWS::Hub h;
  
    PID pid;
    pid.Init(0.15, 0.0, 2.5);
    // TODO: Initialize the pid variable.
  
    h.onMessage([&pid](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(std::string(data).substr(0, length));
        if (s != "") {
          auto j = json::parse(s);
          std::string event = j[0].get<std::string>();
          if (event == "telemetry") {
            // j[1] is the data JSON object
            double cte = std::stod(j[1]["cte"].get<std::string>());
            double speed = std::stod(j[1]["speed"].get<std::string>());
            double angle = std::stod(j[1]["steering_angle"].get<std::string>());
            double steer_value;
            /*
            * TODO: Calcuate steering value here, remember the steering value is
            * [-1, 1].
            * NOTE: Feel free to play around with the throttle and speed. Maybe use
            * another PID controller to control the speed!
            */
            
            pid.UpdateError(cte);
            steer_value = pid.TotalError();
            //speed = 10;
  
            // DEBUG
            std::cout << "CTE: " << cte << " Steering Value: " << steer_value << std::endl;
  
            json msgJson;
            msgJson["steering_angle"] = steer_value;
            msgJson["throttle"] = 0.3;
            auto msg = "42[\"steer\"," + msgJson.dump() + "]";
            std::cout << msg << std::endl;
            ws.send(msg.data(), msg.length(), uWS::OpCode::TEXT);
          }
        } else {
          // Manual driving
          std::string msg = "42[\"manual\",{}]";
          ws.send(msg.data(), msg.length(), uWS::OpCode::TEXT);
        }
      }
    });
  
    // We don't need this since we're not using HTTP but if it's removed the program
    // doesn't compile :-(
    h.onHttpRequest([](uWS::HttpResponse *res, uWS::HttpRequest req, char *data, size_t, size_t) {
      const std::string s = "<h1>Hello world!</h1>";
      if (req.getUrl().valueLength == 1)
      {
        res->end(s.data(), s.length());
      }
      else
      {
        // i guess this should be done more gracefully?
        res->end(nullptr, 0);
      }
    });
  
    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();
  }
  