\\ Original Version was created by Md, Tawsiful Islam
\\ You Can modify the Code as for your needs

#include <AFMotor.h>
#include <NewPing.h>
#include <NewTone.h>
//initial motors pin
AF_DCMotor motor1(1, MOTOR12_1KHZ);
AF_DCMotor motor2(2, MOTOR12_1KHZ);
AF_DCMotor motor3(3, MOTOR34_1KHZ);
AF_DCMotor motor4(4, MOTOR34_1KHZ);

char command;
#define TRIG A0
#define ECHO A1
#define MAX_DISTANCE 100
NewPing sonar(TRIG, ECHO, MAX_DISTANCE);
#define TONE_PIN 10

//defining pins and variables
#define left A3
#define right A4

bool follow = true;

void setup() {
  Serial.begin(9600);  //Set the baud rate to your Bluetooth module.
  pinMode(left, INPUT);
  pinMode(right, INPUT);
}

void loop() {
  int distance = sonar.ping_cm();
  if (distance == 0) {
    distance = 30;
  }

  if (distance <= 20) {
    NewTone(TONE_PIN, 2000);
    back(); 
    int xdistance = sonar.ping_cm();
    if (xdistance == 0) {
      xdistance = 30;
    }
    if (xdistance >= 20) {
      noNewTone(TONE_PIN);
      Stop();
    }
  }
  if (Serial.available() > 0) {
    command = Serial.read();
    Stop();  //initialize with motors stoped

    //Change pin mode only if new command is different from previous
    switch (command) {
      case 'F':
        forward();
        Serial.println("Forward");
        break;
      case 'B':
        back();
        Serial.println("back");
        break;
      case 'L':
        Left();
        Serial.println("left");
        break;
      case 'R':
        Right();
        Serial.println("right");
        break;
      case 'V':
        NewTone(TONE_PIN, 1000);
        break;
      case 'v':
        noNewTone(TONE_PIN);
        break;
      case 'x':
        Serial.println("extra on");
        line_follower();
    }
  }
}

void forward() {
  motor1.setSpeed(255);  //Define Motor PWM (Speed)
  motor1.run(FORWARD);   //rotate the motor clockwise
  motor2.setSpeed(255);
  motor2.run(FORWARD);
  motor3.setSpeed(255);
  motor3.run(FORWARD);
  motor4.setSpeed(255);
  motor4.run(FORWARD);
}
void forward_S() {
  motor1.run(FORWARD);
  motor1.setSpeed(80);
  motor2.run(FORWARD);
  motor2.setSpeed(80);
  motor3.run(FORWARD);
  motor3.setSpeed(80);
  motor4.run(FORWARD);
  motor4.setSpeed(80);
}

void back() {
  motor1.setSpeed(255);  //Define Motor PWM (Speed)
  motor1.run(BACKWARD);  //rotate the motor anti-clockwise
  motor2.setSpeed(255);
  motor2.run(BACKWARD);
  motor3.setSpeed(255);
  motor3.run(BACKWARD);
  motor4.setSpeed(255);
  motor4.run(BACKWARD);
}

void Left() {
  motor1.setSpeed(255);
  motor1.run(BACKWARD);
  motor2.setSpeed(255);
  motor2.run(BACKWARD);
  motor3.setSpeed(255);
  motor3.run(FORWARD);
  motor4.setSpeed(255);
  motor4.run(FORWARD);
}

void Right() {
  motor1.setSpeed(255);
  motor1.run(FORWARD);
  motor2.setSpeed(255);
  motor2.run(FORWARD);
  motor3.setSpeed(255);
  motor3.run(BACKWARD);
  motor4.setSpeed(255);
  motor4.run(BACKWARD);
}

void Stop() {
  motor1.setSpeed(0);
  motor1.run(RELEASE);
  motor2.setSpeed(0);
  motor2.run(RELEASE);
  motor3.setSpeed(0);
  motor3.run(RELEASE);
  motor4.setSpeed(0);
  motor4.run(RELEASE);
}

///////////////////////////////////////////

void line_follower() {

  int i = 87;
  forward();
  delay(70);

  while (follow == true) {
    int distance = sonar.ping_cm();
    if (distance == 0) {
      distance = 30;
    }
    // if (distance <= 15) {
    //   Stop();
    //   NewTone(TONE_PIN, 2400, 1000);
    //   if (distance >= 15) {
    //     noNewTone(TONE_PIN);
    //     forward();
    //     delay(70);
    //   }
    // }
    // if (distance <= 17) {
    //   // advanced_avoid();
    //  NewTone(TONE_PIN, 2400, 1000);
    //   Right();
    //   delay(350);
    //   forward();
    //   delay(270);
    //   Stop();
    //   delay(500);
    //   Left();
    //   delay(350);
    //   Stop();
    //   delay(500);
    //   forward();
    //   delay(300);
    //   Stop();
    //   delay(500);
    //   Left();
    //   delay(350);
    //   forward_S();
    //   while (follow == true) {
    //     if (digitalRead(left) == 0) {
    //       //turn right
    //       Stop();
    //       Left();
    //       delay(300);
    //       break;
    //     }
    //   }
    // }
    if (!digitalRead(left) == 0 && !digitalRead(right) == 0) {
      //Forward
      motor1.run(FORWARD);
      motor1.setSpeed(i);
      motor2.run(FORWARD);
      motor2.setSpeed(i);
      motor3.run(FORWARD);
      motor3.setSpeed(i);
      motor4.run(FORWARD);
      motor4.setSpeed(i);
      Serial.println(("Forward"));
    } else if (!digitalRead(left) == 0 && digitalRead(right) == 0) {
      //turn right
      Stop();
      motor1.setSpeed(200);
      motor1.run(FORWARD);
      motor2.setSpeed(200);
      motor2.run(FORWARD);
      motor3.setSpeed(200);
      motor3.run(BACKWARD);
      motor4.setSpeed(200);
      motor4.run(BACKWARD);
      Serial.println(("Right"));
      delay(70);
    } else if (digitalRead(left) == 0 && !digitalRead(right) == 0) {
      //turn left
      Stop();
      motor1.setSpeed(200);
      motor1.run(BACKWARD);
      motor2.setSpeed(200);
      motor2.run(BACKWARD);
      motor3.setSpeed(200);
      motor3.run(FORWARD);
      motor4.setSpeed(200);
      motor4.run(FORWARD);
      Serial.println(("Left"));
      delay(70);
    } else if (digitalRead(left) == 0 && digitalRead(right) == 0) {
      // stop
      motor1.run(RELEASE);
      motor1.setSpeed(0);
      motor2.run(RELEASE);
      motor2.setSpeed(0);
      motor3.run(RELEASE);
      motor3.setSpeed(0);
      motor4.run(RELEASE);
      motor4.setSpeed(0);
      break;
    }
  }
}

  // void advanced_avoid() {

  //   NewTone(TONE_PIN, 2400, 1000);
  //   Stop();
  //   delay(100);

  //   Right();
  //   delay(350);

  //   Stop();

  //   int rdistance = sonar.ping_cm();
  //   delay(2500);

  //   if (rdistance == 0) {
  //     rdistance == 100;
  //   }
  //   if (rdistance >= 50) {

  //     forward();
  //     delay(300);

  //     Stop();
  //     delay(500);

  //     Left();
  //     delay(350);

  //     Stop();
  //     delay(500);

  //     forward();
  //     delay(350);

  //     Stop();
  //     delay(500);

  //     Left();
  //     delay(350);

  //     forward_S();

  //     while (follow == true) {
  //       if (digitalRead(right) == 0) {
  //         //turn right
  //         Stop();
  //         Right();
  //         delay(300);
  //         break;
  //       }
  //     }
  //   }

  //   else if (rdistance < 15) {
  //     Left();
  //     delay(350);
  //     Stop();
  //     delay(250);
  //     Left();
  //     delay(350);
  //     Stop();

  //     int ldistance = sonar.ping_cm();
  //     delay(2500);

  //     if (ldistance == 0) {
  //       ldistance == 100;
  //     }
  //     if (ldistance < 15) {
  //       NewTone(TONE_PIN, 1000);
  //     }

  //     else {
  //       forward();
  //       delay(300);

  //       Stop();
  //       delay(500);

  //       Right();
  //       delay(350);

  //       Stop();
  //       delay(500);

  //       forward();
  //       delay(350);

  //       Stop();
  //       delay(500);

  //       Right();
  //       delay(350);

  //       forward_S();

  //       while (follow == true) {
  //         if (digitalRead(left) == 0) {
  //           //turn right
  //           Stop();
  //           Left();
  //           delay(300);
  //           break;
  //         }
  //       }
  //     }
  //   }
  // }