#define enablePin 2
#define IN1_L  3
#define IN3_R  6

#define IN2_L  5
#define IN4_R  9

int engineSpeed;
const int BRAKE=0;
const int FORWARDS=1;
const int BACKWARDS=2;
const int RIGHT=3;
const int LEFT=4;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  
  pinMode(enablePin,OUTPUT);
  pinMode(IN1_L,OUTPUT);
  pinMode(IN2_L,OUTPUT);
  pinMode(IN3_R,OUTPUT);
  pinMode(IN4_R,OUTPUT);
  
  digitalWrite(enablePin, HIGH);  
  
  engineSpeed=140;
}

void go(int dir){
 if(dir==BRAKE){
  digitalWrite(IN1_L,LOW);
  digitalWrite(IN2_L,LOW);
  digitalWrite(IN3_R,LOW);
  digitalWrite(IN4_R,LOW);
 }else if(dir==FORWARDS){
  digitalWrite(IN2_L, LOW);
  digitalWrite(IN4_R, LOW);
  
  analogWrite(IN1_L, engineSpeed);
  analogWrite(IN3_R, engineSpeed);
 } else if(dir == BACKWARDS){
  digitalWrite(IN1_L, LOW);
  digitalWrite(IN3_R, LOW);
  
  analogWrite(IN2_L, engineSpeed);
  analogWrite(IN4_R, engineSpeed); 
 }else if(dir==LEFT){
  analogWrite(IN1_L, LOW);
  analogWrite(IN2_L, engineSpeed);
  analogWrite(IN3_R, engineSpeed);
  analogWrite(IN4_R, LOW);
  
 } else if(dir == RIGHT){
  analogWrite(IN1_L, engineSpeed);
  analogWrite(IN2_L, LOW);
  analogWrite(IN3_R, LOW);
  analogWrite(IN4_R, engineSpeed);
 }
}

void loop() {
  if(Serial.available()){
    byte b = Serial.read();
    if(b==49){
      Serial.println("Fast"); 
         if(engineSpeed+20<=250){
         engineSpeed+=20; 
      }
    }
    else if(b==50){
      Serial.println("Slow");
      if(engineSpeed-20>0){
         engineSpeed-=20; 
      }
     }else if(b==97){
      Serial.println("Left");
      go(LEFT);
    }else if(b==100){
      Serial.println("Right"); 
      go(RIGHT);
    }else if(b==119){
      Serial.println("Forward");
      go(FORWARDS);
    }else if(b==115){
      Serial.println("Backward"); 
      go(BACKWARDS);
    }
    else if(b==112){
      Serial.println("Stop"); 
      go(BRAKE);
    }
    else {
      Serial.println(b);
    }
  }
}