text: #include <fstream>
  #include <math.h>
  #include <uWS/uWS.h>
  #include <chrono>
  #include <iostream>
  #include <thread>
  #include <vector>
  #include "Eigen-3.3/Eigen/Core"
  #include "Eigen-3.3/Eigen/QR"
  #include "json.hpp"
  #include "spline.h"
  
  using namespace std;
  
  // 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.
  string hasData(string s) {
    auto found_null = s.find("null");
    auto b1 = s.find_first_of("[");
    auto b2 = s.find_first_of("}");
    if (found_null != string::npos) {
      return "";
    } else if (b1 != string::npos && b2 != string::npos) {
      return s.substr(b1, b2 - b1 + 2);
    }
    return "";
  }
  
  double distance(double x1, double y1, double x2, double y2)
  {
  	return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
  }
  int ClosestWaypoint(double x, double y, const vector<double> &maps_x, const vector<double> &maps_y)
  {
  
  	double closestLen = 100000; //large number
  	int closestWaypoint = 0;
  
  	for(int i = 0; i < maps_x.size(); i++)
  	{
  		double map_x = maps_x[i];
  		double map_y = maps_y[i];
  		double dist = distance(x,y,map_x,map_y);
  		if(dist < closestLen)
  		{
  			closestLen = dist;
  			closestWaypoint = i;
  		}
  
  	}
  
  	return closestWaypoint;
  
  }
  
  int NextWaypoint(double x, double y, double theta, const vector<double> &maps_x, const vector<double> &maps_y)
  {
  
  	int closestWaypoint = ClosestWaypoint(x,y,maps_x,maps_y);
  
  	double map_x = maps_x[closestWaypoint];
  	double map_y = maps_y[closestWaypoint];
  
  	double heading = atan2( (map_y-y),(map_x-x) );
  
  	double angle = abs(theta-heading);
  
  	if(angle > pi()/4)
  	{
  		closestWaypoint++;
  	}
  
  	return closestWaypoint;
  
  }
  
  // Transform from Cartesian x,y coordinates to Frenet s,d coordinates
  vector<double> getFrenet(double x, double y, double theta, const vector<double> &maps_x, const vector<double> &maps_y)
  {
  	int next_wp = NextWaypoint(x,y, theta, maps_x,maps_y);
  
  	int prev_wp;
  	prev_wp = next_wp-1;
  	if(next_wp == 0)
  	{
  		prev_wp  = maps_x.size()-1;
  	}
  
  	double n_x = maps_x[next_wp]-maps_x[prev_wp];
  	double n_y = maps_y[next_wp]-maps_y[prev_wp];
  	double x_x = x - maps_x[prev_wp];
  	double x_y = y - maps_y[prev_wp];
  
  	// find the projection of x onto n
  	double proj_norm = (x_x*n_x+x_y*n_y)/(n_x*n_x+n_y*n_y);
  	double proj_x = proj_norm*n_x;
  	double proj_y = proj_norm*n_y;
  
  	double frenet_d = distance(x_x,x_y,proj_x,proj_y);
  
  	//see if d value is positive or negative by comparing it to a center point
  
  	double center_x = 1000-maps_x[prev_wp];
  	double center_y = 2000-maps_y[prev_wp];
  	double centerToPos = distance(center_x,center_y,x_x,x_y);
  	double centerToRef = distance(center_x,center_y,proj_x,proj_y);
  
  	if(centerToPos <= centerToRef)
  	{
  		frenet_d *= -1;
  	}
  
  	// calculate s value
  	double frenet_s = 0;
  	for(int i = 0; i < prev_wp; i++)
  	{
  		frenet_s += distance(maps_x[i],maps_y[i],maps_x[i+1],maps_y[i+1]);
  	}
  
  	frenet_s += distance(0,0,proj_x,proj_y);
  
  	return {frenet_s,frenet_d};
  
  }
  
  // Transform from Frenet s,d coordinates to Cartesian x,y
  vector<double> getXY(double s, double d, const vector<double> &maps_s, const vector<double> &maps_x, const vector<double> &maps_y)
  {
  	int prev_wp = -1;
  
  	while(s > maps_s[prev_wp+1] && (prev_wp < (int)(maps_s.size()-1) ))
  	{
  		prev_wp++;
  	}
  
  	int wp2 = (prev_wp+1)%maps_x.size();
  
  	double heading = atan2((maps_y[wp2]-maps_y[prev_wp]),(maps_x[wp2]-maps_x[prev_wp]));
  	// the x,y,s along the segment
  	double seg_s = (s-maps_s[prev_wp]);
  
  	double seg_x = maps_x[prev_wp]+seg_s*cos(heading);
  	double seg_y = maps_y[prev_wp]+seg_s*sin(heading);
  
  	double perp_heading = heading-pi()/2;
  
  	double x = seg_x + d*cos(perp_heading);
  	double y = seg_y + d*sin(perp_heading);
  
  	return {x,y};
  
  }
  
  int main() {
    uWS::Hub h;
  
    // Load up map values for waypoint's x,y,s and d normalized normal vectors
    vector<double> map_waypoints_x;
    vector<double> map_waypoints_y;
    vector<double> map_waypoints_s;
    vector<double> map_waypoints_dx;
    vector<double> map_waypoints_dy;
  
    // Waypoint map to read from
    string map_file_ = "../data/highway_map.csv";
    // The max s value before wrapping around the track back to 0
    double max_s = 6945.554;
  
    ifstream in_map_(map_file_.c_str(), ifstream::in);
  
    string line;
    while (getline(in_map_, line)) {
    	istringstream iss(line);
    	double x;
    	double y;
    	float s;
    	float d_x;
    	float d_y;
    	iss >> x;
    	iss >> y;
    	iss >> s;
    	iss >> d_x;
    	iss >> d_y;
    	map_waypoints_x.push_back(x);
    	map_waypoints_y.push_back(y);
    	map_waypoints_s.push_back(s);
    	map_waypoints_dx.push_back(d_x);
    	map_waypoints_dy.push_back(d_y);
    }
  
    // Car's lane. Starting at middle lane.
    int lane = 1;
  
    // Reference velocity.
    double ref_vel = 0.0; // mph
  
    h.onMessage([&ref_vel, &lane, &map_waypoints_x,&map_waypoints_y,&map_waypoints_s,&map_waypoints_dx,&map_waypoints_dy]
      (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
      //auto sdata = string(data).substr(0, length);
      //cout << sdata << endl;
      if (length && length > 2 && data[0] == '4' && data[1] == '2') {
  
        auto s = hasData(data);
  
        if (s != "") {
          auto j = json::parse(s);
  
          string event = j[0].get<string>();
  
          if (event == "telemetry") {
            // j[1] is the data JSON object
  
          	// Main car's localization Data
            	double car_x = j[1]["x"];
            	double car_y = j[1]["y"];
            	double car_s = j[1]["s"];
            	double car_d = j[1]["d"];
            	double car_yaw = j[1]["yaw"];
            	double car_speed = j[1]["speed"];
  
            	// Previous path data given to the Planner
            	auto previous_path_x = j[1]["previous_path_x"];
            	auto previous_path_y = j[1]["previous_path_y"];
            	// Previous path's end s and d values
            	double end_path_s = j[1]["end_path_s"];
            	double end_path_d = j[1]["end_path_d"];
  
            	// Sensor Fusion Data, a list of all other cars on the same side of the road.
            	auto sensor_fusion = j[1]["sensor_fusion"];
  
              // Provided previous path point size.
              int prev_size = previous_path_x.size();
  
              // Preventing collitions.
              if (prev_size > 0) {
                car_s = end_path_s;
              }
  
              // Prediction : Analysing other cars positions.
              bool car_ahead = false;
              bool car_left = false;
              bool car_righ = false;
              for ( int i = 0; i < sensor_fusion.size(); i++ ) {
                  float d = sensor_fusion[i][6];
                  int car_lane = -1;
                  // is it on the same lane we are
                  if ( d > 0 && d < 4 ) {
                    car_lane = 0;
                  } else if ( d > 4 && d < 8 ) {
                    car_lane = 1;
                  } else if ( d > 8 && d < 12 ) {
                    car_lane = 2;
                  }
                  if (car_lane < 0) {
                    continue;
                  }
                  // Find car speed.
                  double vx = sensor_fusion[i][3];
                  double vy = sensor_fusion[i][4];
                  double check_speed = sqrt(vx*vx + vy*vy);
                  double check_car_s = sensor_fusion[i][5];
                  // Estimate car s position after executing previous trajectory.
                  check_car_s += ((double)prev_size*0.02*check_speed);
  
                  if ( car_lane == lane ) {
                    // Car in our lane.
                    car_ahead |= check_car_s > car_s && check_car_s - car_s < 30;
                  } else if ( car_lane - lane == -1 ) {
                    // Car left
                    car_left |= car_s - 30 < check_car_s && car_s + 30 > check_car_s;
                  } else if ( car_lane - lane == 1 ) {
                    // Car right
                    car_righ |= car_s - 30 < check_car_s && car_s + 30 > check_car_s;
                  }
              }
  
              // Behavior : Let's see what to do.
              double speed_diff = 0;
              const double MAX_SPEED = 49.5;
              const double MAX_ACC = .224;
              if ( car_ahead ) { // Car ahead
                if ( !car_left && lane > 0 ) {
                  // if there is no car left and there is a left lane.
                  lane--; // Change lane left.
                } else if ( !car_righ && lane != 2 ){
                  // if there is no car right and there is a right lane.
                  lane++; // Change lane right.
                } else {
                  speed_diff -= MAX_ACC;
                }
              } else {
                if ( lane != 1 ) { // if we are not on the center lane.
                  if ( ( lane == 0 && !car_righ ) || ( lane == 2 && !car_left ) ) {
                    lane = 1; // Back to center.
                  }
                }
                if ( ref_vel < MAX_SPEED ) {
                  speed_diff += MAX_ACC;
                }
              }
  
            	vector<double> ptsx;
              vector<double> ptsy;
  
              double ref_x = car_x;
              double ref_y = car_y;
              double ref_yaw = deg2rad(car_yaw);
  
              // Do I have have previous points
              if ( prev_size < 2 ) {
                  // There are not too many...
                  double prev_car_x = car_x - cos(car_yaw);
                  double prev_car_y = car_y - sin(car_yaw);
  
                  ptsx.push_back(prev_car_x);
                  ptsx.push_back(car_x);
  
                  ptsy.push_back(prev_car_y);
                  ptsy.push_back(car_y);
              } else {
                  // Use the last two points.
                  ref_x = previous_path_x[prev_size - 1];
                  ref_y = previous_path_y[prev_size - 1];
  
                  double ref_x_prev = previous_path_x[prev_size - 2];
                  double ref_y_prev = previous_path_y[prev_size - 2];
                  ref_yaw = atan2(ref_y-ref_y_prev, ref_x-ref_x_prev);
  
                  ptsx.push_back(ref_x_prev);
                  ptsx.push_back(ref_x);
  
                  ptsy.push_back(ref_y_prev);
                  ptsy.push_back(ref_y);
              }
  
              // Setting up target points in the future.
              vector<double> next_wp0 = getXY(car_s + 30, 2 + 4*lane, map_waypoints_s, map_waypoints_x, map_waypoints_y);
              vector<double> next_wp1 = getXY(car_s + 60, 2 + 4*lane, map_waypoints_s, map_waypoints_x, map_waypoints_y);
              vector<double> next_wp2 = getXY(car_s + 90, 2 + 4*lane, map_waypoints_s, map_waypoints_x, map_waypoints_y);
  
              ptsx.push_back(next_wp0[0]);
              ptsx.push_back(next_wp1[0]);
              ptsx.push_back(next_wp2[0]);
  
              ptsy.push_back(next_wp0[1]);
              ptsy.push_back(next_wp1[1]);
              ptsy.push_back(next_wp2[1]);
  
              // Making coordinates to local car coordinates.
              for ( int i = 0; i < ptsx.size(); i++ ) {
                double shift_x = ptsx[i] - ref_x;
                double shift_y = ptsy[i] - ref_y;
  
                ptsx[i] = shift_x * cos(0 - ref_yaw) - shift_y * sin(0 - ref_yaw);
                ptsy[i] = shift_x * sin(0 - ref_yaw) + shift_y * cos(0 - ref_yaw);
              }
  
              // Create the spline.
              tk::spline s;
              s.set_points(ptsx, ptsy);
  
              // Output path points from previous path for continuity.
            	vector<double> next_x_vals;
            	vector<double> next_y_vals;
              for ( int i = 0; i < prev_size; i++ ) {
                next_x_vals.push_back(previous_path_x[i]);
                next_y_vals.push_back(previous_path_y[i]);
              }
  
              // Calculate distance y position on 30 m ahead.
              double target_x = 30.0;
              double target_y = s(target_x);
              double target_dist = sqrt(target_x*target_x + target_y*target_y);
  
              double x_add_on = 0;
  
              for( int i = 1; i < 50 - prev_size; i++ ) {
                ref_vel += speed_diff;
                if ( ref_vel > MAX_SPEED ) {
                  ref_vel = MAX_SPEED;
                } else if ( ref_vel < MAX_ACC ) {
                  ref_vel = MAX_ACC;
                }
                double N = target_dist/(0.02*ref_vel/2.24);
                double x_point = x_add_on + target_x/N;
                double y_point = s(x_point);
  
                x_add_on = x_point;
  
                double x_ref = x_point;
                double y_ref = y_point;
  
                x_point = x_ref * cos(ref_yaw) - y_ref * sin(ref_yaw);
                y_point = x_ref * sin(ref_yaw) + y_ref * cos(ref_yaw);
  
                x_point += ref_x;
                y_point += ref_y;
  
                next_x_vals.push_back(x_point);
                next_y_vals.push_back(y_point);
              }
  
              json msgJson;
  
            	msgJson["next_x"] = next_x_vals;
            	msgJson["next_y"] = next_y_vals;
  
            	auto msg = "42[\"control\","+ msgJson.dump()+"]";
  
            	//this_thread::sleep_for(chrono::milliseconds(1000));
            	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();
  }