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

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

volatile int seconds, minutes, hours;

const int buttonPin = 2;
volatile int buttonState = 0;

//adjust values here, have to comment above as well
//volatile int seconds = 50;
//volatile int minutes = 2;
//volatile int hours = 1;

void setup() {
  // put your setup code here, to run once:
  pinMode(buttonPin, INPUT);
  attachInterrupt(digitalPinToInterrupt(buttonPin), buttonInterrupt, CHANGE);

  Serial.begin(9600);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);

  display.display();
  display.clearDisplay(); 
  display.setTextSize(1); 
  display.setTextColor(WHITE); 
  display.setCursor(0,0);

  cli();//stop interrupts

  TCCR1A = 0;// set entire TCCR1A register to 0
  TCCR1B = 0;// same for TCCR1B
  TCNT1  = 0;//initialize counter value to 0
  // set compare match register for 1hz increments
  OCR1A = 15624;// = (16*10^6) / (1*1024) - 1 (must be <65536)
  // turn on CTC mode (counter cleared to 0)
  TCCR1B |= (1 << WGM12);
  // Set CS12 and CS10 bits for 1024 prescaler
  TCCR1B |= (1 << CS12) | (1 << CS10);  
  // enable timer compare interrupt
  TIMSK1 |= (1 << OCIE1A);

  sei();//allow interrupts
  display.clearDisplay();
}
 
ISR(TIMER1_COMPA_vect){
    seconds ++; //increment second counter
    if(seconds == 60) 
    {
    seconds = 0; //reset sec counter
    minutes ++; //increment min counter
//Update minute counter
    if(minutes == 60)
    {
    minutes = 0; //reset min counter
    hours ++; //increment hr counter
//Update hour counter
    if(hours == 24)
    {
    hours = 0; //reset hr counter
    }     
  }
 }
 if (hours < 10) {
    Serial.print("0"); // add leading zero for hours less than 10
  }
  Serial.print(hours);
  Serial.print(":");
  if (minutes < 10) {
    Serial.print("0"); // add leading zero for minutes less than 10
  }
  Serial.print(minutes);
  Serial.print(":");
  if (seconds < 10) {
    Serial.print("0"); // add leading zero for seconds less than 10
  }
  Serial.print(seconds);
  Serial.println(); 
}
void loop() {
  // put your main code here, to run repeatedly:
    display.clearDisplay(); 
    display.setCursor(0,0);
    if (hours < 10) {
    display.print("0"); // add leading zero for hours less than 10
  }
    display.print(hours);
    display.print(":");
  if (minutes < 10) {
    display.print("0"); // add leading zero for minutes less than 10
  }
    display.print(minutes);
    display.print(":");
  if (seconds < 10) {
    display.print("0"); // add leading zero for seconds less than 10
  }
  display.print(seconds);
  display.display();

}

void buttonInterrupt() {
  buttonState = 1;
}