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

// Define button pins
const int buttonStartPin = 15;
const int buttonStopPin = 2;
const int buttonResetPin = 4;

// Define display
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// Variables for stopwatch
unsigned long startTime = 0;
unsigned long elapsedTime = 0;
bool running = false;

void setup() {
  pinMode(buttonStartPin, INPUT_PULLUP);
  pinMode(buttonStopPin, INPUT_PULLUP);
  pinMode(buttonResetPin, INPUT_PULLUP);
  
  // Initialize display
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { // 0x3C is a common I2C address for SSD1306
    Serial.println(F("SSD1306 allocation failed"));
    for(;;);
  }
  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0,0);
  display.print("Stopwatch");
  display.display();
  delay(2000);
  display.clearDisplay();
}

void loop() {
  // Check start button
  if (digitalRead(buttonStartPin) == HIGH) {
    if (!running) {
      running = true;
      startTime = millis() - elapsedTime;
    }
  }

  // Check stop button
  if (digitalRead(buttonStopPin) == HIGH) {
    if (running) {
      running = false;
      elapsedTime = millis() - startTime;
    }
  }

  // Check reset button
  if (digitalRead(buttonResetPin) == HIGH) {
    running = false;
    elapsedTime = 0;
  }

  // Update display
  if (running) {
    elapsedTime = millis() - startTime;
  }

  display.clearDisplay();
  display.setCursor(0, 0);
  display.print("Time: ");
  display.print(elapsedTime / 1000);
  display.print(".");
  display.print((elapsedTime % 1000) / 100);
  display.display();
  delay(100);
}