#include <Wire.h>
#include <Adafruit_SSD1306.h>

// OLED display resolution
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

// OLED display object
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire);

// Pin definitions for the buttons
const int bt_start = 2;
const int bt_stop  = 3;
const int bt_reset = 4;


int hh=0, mm=0, ss=0, ms=0; 
int start=0;
int stp=digitalRead (bt_stop);
bool timerStart = false;


void setup() {
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // initialize OLED display
  display.clearDisplay(); // clear the display's memory
  display.display(); // update the display
  
  // Set the button pins as inputs
  pinMode(bt_start, INPUT_PULLUP);
pinMode(bt_stop,  INPUT_PULLUP);
pinMode(bt_reset, INPUT_PULLUP);

noInterrupts();         // disable all interrupts
 TCCR1A = 0;             // set entire TCCR1A register to 0  //set timer1 interrupt at 1kHz  // 1 ms
 TCCR1B = 0;             // same for TCCR1B
 TCNT1  = 0;             // set timer count for 1khz increments
 OCR1A = 1999;           // = (16*10^6) / (1000*8) - 1
 //had to use 16 bit timer1 for this bc 1999>255, but could switch to timers 0 or 2 with larger prescaler
 // turn on CTC mode
 TCCR1B |= (1 << WGM12); // Set CS11 bit for 8 prescaler
 TCCR1B |= (1 << CS11);  // enable timer compare interrupt
 TIMSK1 |= (1 << OCIE1A);
 interrupts();           // enable
 
}

void loop() {

   if(digitalRead (bt_start) == 0){ 
  
start=start+1;

}
else{start=0;}
if(start==1){
  ms=0, ss=0, mm=0, hh=0; // Reset stopwatch 

timerStart = true; // Start stopwatch 

}


if (stp == 1) {
if(digitalRead (bt_stop) == 0){
   
timerStart = false; // Stop stopwatch 
}
}
else if (stp == 0) {
if(!digitalRead (bt_stop) == 0){

timerStart = false; // Stop stopwatch 

}
}
if(digitalRead (bt_reset) == 0){ 
  
ms=0, ss=0, mm=0, hh=0; // Reset stopwatch 

}
stp=digitalRead (bt_stop);


  display.clearDisplay(); // clear the display's memory
  display.setTextSize(2); // set text size to 2
  display.setTextColor(WHITE); // set text color to white
    
    // Display "Timer" on the first line
  display.setCursor(12, 05);
  display.println("*Sverker*");
  display.setCursor(25, 28);
  
  display.setCursor(12, 50);
  display.println("MM:SS:Mls");
  
  // Display the elapsed time in the middle of the second line
  if (timerStart==true) {
    
display.setCursor(12, 28);    
display.print((mm/10)%10);
display.print(mm%10);
display.print(":");
display.print((ss/10)%10);
display.print(ss%10);
display.print(":");
display.print((ms/100)%10);
display.print((ms/10)%10);
display.print(ms%10);
  } 
  else 
  {
display.setCursor(12, 28);    
display.print((mm/10)%10);
display.print(mm%10);
display.print(":");
display.print((ss/10)%10);
display.print(ss%10);
display.print(":");
display.print((ms/100)%10);
display.print((ms/10)%10);
display.print(ms%10);

  }
  display.display(); // update the display
}


ISR(TIMER1_COMPA_vect){   
if(timerStart == true){ms=ms+1;
if(ms>999){ms=0;ss=ss+1;
if(ss>59){ss=0; mm=mm+1;}
if(mm>59){mm=0; hh=hh+1;}
  }
}
    }