class LaneDetector 
{
private:
 double img_size;
 double img_center;
 bool left_flag = false; // Tells us if there's left boundary of lane detected
 bool right_flag = false; // Tells us if there's right boundary of lane detected
 cv::Point right_b; // Members of both line equations of the lane boundaries:
 double right_m; // y = m*x + b
 cv::Point left_b; //
 double left_m; //

public:
 cv::Mat deNoise(cv::Mat inputImage); // Apply Gaussian blurring to the input Image
 cv::Mat edgeDetector(cv::Mat img_noise); // Filter the image to obtain only edges
 cv::Mat mask(cv::Mat img_edges); // Mask the edges image to only care about ROI
 std::vector<cv::Vec4i> houghLines(cv::Mat img_mask); // Detect Hough lines in masked edges image
 std::vector<std::vector<cv::Vec4i> > lineSeparation(std::vector<cv::Vec4i> lines, cv::Mat img_edges); // Sprt detected lines by their slope into right and left lines
 std::vector<cv::Point> regression(std::vector<std::vector<cv::Vec4i> > left_right_lines, cv::Mat inputImage); // Get only one line for each side of the lane
 std::string predictTurn(); // Determine if the lane is turning or not by calculating the position of the vanishing point
 int plotLane(cv::Mat inputImage, std::vector<cv::Point> lane, std::string turn); // Plot the resultant lane and turn prediction in the frame.
};

*@file LaneDetector.cpp
*@author Miguel Maestre Trueba
*@brief Definition of all the function that form part of the LaneDetector class.
*@brief The class will take RGB images as inputs and will output the same RGB image but
*@brief with the plot of the detected lanes and the turn prediction.
*/
#include <string>
#include <vector>
#include <opencv2/opencv.hpp>
#include "LaneDetector.h"

// IMAGE BLURRING
/**
*@brief Apply gaussian filter to the input image to denoise it
*@param inputImage is the frame of a video in which the
*@param lane is going to be detected
*@return Blurred and denoised image
*/
cv::Mat LaneDetector::deNoise(cv::Mat inputImage) {
 cv::Mat output;

 cv::GaussianBlur(inputImage, output, cv::Size(3, 3), 0, 0);

 return output;
}

// EDGE DETECTION
/**
*@brief Detect all the edges in the blurred frame by filtering the image
*@param img_noise is the previously blurred frame
*@return Binary image with only the edges represented in white
*/
cv::Mat LaneDetector::edgeDetector(cv::Mat img_noise) {
 cv::Mat output;
 cv::Mat kernel;
 cv::Point anchor;

 // Convert image from RGB to gray
 cv::cvtColor(img_noise, output, cv::COLOR_RGB2GRAY);
 // Binarize gray image
 cv::threshold(output, output, 140, 255, cv::THRESH_BINARY);

 // Create the kernel [-1 0 1]
 // This kernel is based on the one found in the
 // Lane Departure Warning System by Mathworks
 anchor = cv::Point(-1, -1);
 kernel = cv::Mat(1, 3, CV_32F);
 kernel.at<float>(0, 0) = -1;
 kernel.at<float>(0, 1) = 0;
 kernel.at<float>(0, 2) = 1;

 // Filter the binary image to obtain the edges
 cv::filter2D(output, output, -1, kernel, anchor, 0, cv::BORDER_DEFAULT);
 cv::imshow("output", output);
 return output;
}

// MASK THE EDGE IMAGE
/**
*@brief Mask the image so that only the edges that form part of the lane are detected
*@param img_edges is the edges image from the previous function
*@return Binary image with only the desired edges being represented
*/
cv::Mat LaneDetector::mask(cv::Mat img_edges) {
 cv::Mat output;
 cv::Mat mask = cv::Mat::zeros(img_edges.size(), img_edges.type());
 cv::Point pts[4] = {
 cv::Point(210, 720),
 cv::Point(550, 450),
 cv::Point(717, 450),
 cv::Point(1280, 720)
 };

 // Create a binary polygon mask
 cv::fillConvexPoly(mask, pts, 4, cv::Scalar(255, 0, 0));
 // Multiply the edges image and the mask to get the output
 cv::bitwise_and(img_edges, mask, output);

 return output;
}

// HOUGH LINES
/**
*@brief Obtain all the line segments in the masked images which are going to be part of the lane boundaries
*@param img_mask is the masked binary image from the previous function
*@return Vector that contains all the detected lines in the image
*/
std::vector<cv::Vec4i> LaneDetector::houghLines(cv::Mat img_mask) {
 std::vector<cv::Vec4i> line;

 // rho and theta are selected by trial and error
 HoughLinesP(img_mask, line, 1, CV_PI / 180, 20, 20, 30);

 return line;
}

// SORT RIGHT AND LEFT LINES
/**
*@brief Sort all the detected Hough lines by slope.
*@brief The lines are classified into right or left depending
*@brief on the sign of their slope and their approximate location
*@param lines is the vector that contains all the detected lines
*@param img_edges is used for determining the image center
*@return The output is a vector(2) that contains all the classified lines
*/
std::vector<std::vector<cv::Vec4i> > LaneDetector::lineSeparation(std::vector<cv::Vec4i> lines, cv::Mat img_edges) {
 std::vector<std::vector<cv::Vec4i> > output(2);
 size_t j = 0;
 cv::Point ini;
 cv::Point fini;
 double slope_thresh = 0.3;
 std::vector<double> slopes;
 std::vector<cv::Vec4i> selected_lines;
 std::vector<cv::Vec4i> right_lines, left_lines;

 // Calculate the slope of all the detected lines
 for (auto i : lines) {
 ini = cv::Point(i[0], i[1]);
 fini = cv::Point(i[2], i[3]);

 // Basic algebra: slope = (y1 - y0)/(x1 - x0)
 double slope = (static_cast<double>(fini.y) - static_cast<double>(ini.y)) / (static_cast<double>(fini.x) - static_cast<double>(ini.x) + 0.00001);

 // If the slope is too horizontal, discard the line
 // If not, save them and their respective slope
 if (std::abs(slope) > slope_thresh) {
 slopes.push_back(slope);
 selected_lines.push_back(i);
 }
 }

 // Split the lines into right and left lines
 img_center = static_cast<double>((img_edges.cols / 2));
 while (j < selected_lines.size()) {
 ini = cv::Point(selected_lines[j][0], selected_lines[j][1]);
 fini = cv::Point(selected_lines[j][2], selected_lines[j][3]);

 // Condition to classify line as left side or right side
 if (slopes[j] > 0 && fini.x > img_center && ini.x > img_center) {
 right_lines.push_back(selected_lines[j]);
 right_flag = true;
 }
 else if (slopes[j] < 0 && fini.x < img_center && ini.x < img_center) {
 left_lines.push_back(selected_lines[j]);
 left_flag = true;
 }
 j++;
 }

 output[0] = right_lines;
 output[1] = left_lines;

 return output;
}

// REGRESSION FOR LEFT AND RIGHT LINES
/**
*@brief Regression takes all the classified line segments initial and final points and fits a new lines out of them using the method of least squares.
*@brief This is done for both sides, left and right.
*@param left_right_lines is the output of the lineSeparation function
*@param inputImage is used to select where do the lines will end
*@return output contains the initial and final points of both lane boundary lines
*/
std::vector<cv::Point> LaneDetector::regression(std::vector<std::vector<cv::Vec4i> > left_right_lines, cv::Mat inputImage) {
 std::vector<cv::Point> output(4);
 cv::Point ini;
 cv::Point fini;
 cv::Point ini2;
 cv::Point fini2;
 cv::Vec4d right_line;
 cv::Vec4d left_line;
 std::vector<cv::Point> right_pts;
 std::vector<cv::Point> left_pts;

 // If right lines are being detected, fit a line using all the init and final points of the lines
 if (right_flag == true) {
 for (auto i : left_right_lines[0]) {
 ini = cv::Point(i[0], i[1]);
 fini = cv::Point(i[2], i[3]);

 right_pts.push_back(ini);
 right_pts.push_back(fini);
 }

 if (right_pts.size() > 0) {
 // The right line is formed here
 cv::fitLine(right_pts, right_line, CV_DIST_L2, 0, 0.01, 0.01);
 right_m = right_line[1] / right_line[0];
 right_b = cv::Point(right_line[2], right_line[3]);
 }
 }

 // If left lines are being detected, fit a line using all the init and final points of the lines
 if (left_flag == true) {
 for (auto j : left_right_lines[1]) {
 ini2 = cv::Point(j[0], j[1]);
 fini2 = cv::Point(j[2], j[3]);

 left_pts.push_back(ini2);
 left_pts.push_back(fini2);
 }

 if (left_pts.size() > 0) {
 // The left line is formed here
 cv::fitLine(left_pts, left_line, CV_DIST_L2, 0, 0.01, 0.01);
 left_m = left_line[1] / left_line[0];
 left_b = cv::Point(left_line[2], left_line[3]);
 }
 }

 // One the slope and offset points have been obtained, apply the line equation to obtain the line points
 int ini_y = inputImage.rows;
 int fin_y = 470;

 double right_ini_x = ((ini_y - right_b.y) / right_m) + right_b.x;
 double right_fin_x = ((fin_y - right_b.y) / right_m) + right_b.x;

 double left_ini_x = ((ini_y - left_b.y) / left_m) + left_b.x;
 double left_fin_x = ((fin_y - left_b.y) / left_m) + left_b.x;

 output[0] = cv::Point(right_ini_x, ini_y);
 output[1] = cv::Point(right_fin_x, fin_y);
 output[2] = cv::Point(left_ini_x, ini_y);
 output[3] = cv::Point(left_fin_x, fin_y);

 return output;
}

// TURN PREDICTION
/**
*@brief Predict if the lane is turning left, right or if it is going straight
*@brief It is done by seeing where the vanishing point is with respect to the center of the image
*@return String that says if there is left or right turn or if the road is straight
*/
std::string LaneDetector::predictTurn() {
 std::string output;
 double vanish_x;
 double thr_vp = 10;

 // The vanishing point is the point where both lane boundary lines intersect
 vanish_x = static_cast<double>(((right_m*right_b.x) - (left_m*left_b.x) - right_b.y + left_b.y) / (right_m - left_m));

 // The vanishing points location determines where is the road turning
 if (vanish_x < (img_center - thr_vp))
 output = "Left Turn";
 else if (vanish_x >(img_center + thr_vp))
 output = "Right Turn";
 else if (vanish_x >= (img_center - thr_vp) && vanish_x <= (img_center + thr_vp))
 output = "Straight";

 return output;
}

// PLOT RESULTS
/**
*@brief This function plots both sides of the lane, the turn prediction message and a transparent polygon that covers the area inside the lane boundaries
*@param inputImage is the original captured frame
*@param lane is the vector containing the information of both lines
*@param turn is the output string containing the turn information
*@return The function returns a 0
*/
int LaneDetector::plotLane(cv::Mat inputImage, std::vector<cv::Point> lane, std::string turn) {
 std::vector<cv::Point> poly_points;
 cv::Mat output;

 // Create the transparent polygon for a better visualization of the lane
 inputImage.copyTo(output);
 poly_points.push_back(lane[2]);
 poly_points.push_back(lane[0]);
 poly_points.push_back(lane[1]);
 poly_points.push_back(lane[3]);
 cv::fillConvexPoly(output, poly_points, cv::Scalar(0, 0, 255), CV_AA, 0);
 cv::addWeighted(output, 0.3, inputImage, 1.0 - 0.3, 0, inputImage);

 // Plot both lines of the lane boundary
 cv::line(inputImage, lane[0], lane[1], cv::Scalar(0, 255, 255), 5, CV_AA);
 cv::line(inputImage, lane[2], lane[3], cv::Scalar(0, 255, 255), 5, CV_AA);

 // Plot the turn message
 cv::putText(inputImage, turn, cv::Point(50, 90), cv::FONT_HERSHEY_COMPLEX_SMALL, 3, cvScalar(0, 255, 0), 1, CV_AA);

 // Show the final output image
 cv::namedWindow("Lane", CV_WINDOW_AUTOSIZE);
 cv::imshow("Lane", inputImage);
 return 0;
}

#include <iostream>
#include <string>
#include <vector>
#include <opencv2/opencv.hpp>
#include "LaneDetector.h"
//#include "LaneDetector.cpp"

/**
*@brief Function main that runs the main algorithm of the lane detection.
*@brief It will read a video of a car in the highway and it will output the
*@brief same video but with the plotted detected lane
*@param argv[] is a string to the full path of the demo video
*@return flag_plot tells if the demo has sucessfully finished
*/
int main() {
 
 // The input argument is the location of the video
 cv::VideoCapture cap("challenge_video.mp4");
 if (!cap.isOpened())
 return -1;

 LaneDetector lanedetector; // Create the class object
 cv::Mat frame;
 cv::Mat img_denoise;
 cv::Mat img_edges;
 cv::Mat img_mask;
 cv::Mat img_lines;
 std::vector<cv::Vec4i> lines;
 std::vector<std::vector<cv::Vec4i> > left_right_lines;
 std::vector<cv::Point> lane;
 std::string turn;
 int flag_plot = -1;
 int i = 0;

 // Main algorithm starts. Iterate through every frame of the video
 while (i < 540) {
 // Capture frame
 if (!cap.read(frame))
 break;

 // Denoise the image using a Gaussian filter
 img_denoise = lanedetector.deNoise(frame);

 // Detect edges in the image
 img_edges = lanedetector.edgeDetector(img_denoise);

 // Mask the image so that we only get the ROI
 img_mask = lanedetector.mask(img_edges);

 // Obtain Hough lines in the cropped image
 lines = lanedetector.houghLines(img_mask);

 if (!lines.empty())
 {
 // Separate lines into left and right lines
 left_right_lines = lanedetector.lineSeparation(lines, img_edges);

 // Apply regression to obtain only one line for each side of the lane
 lane = lanedetector.regression(left_right_lines, frame);

 // Predict the turn by determining the vanishing point of the the lines
 turn = lanedetector.predictTurn();

 // Plot lane detection
 flag_plot = lanedetector.plotLane(frame, lane, turn);

 i += 1;
 cv::waitKey(25);
 }
 else {
 flag_plot = -1;
 }
 }
 return flag_plot;
}