#include <Arduino.h>

// Define pin numbers for the buttons
#define START_BUTTON_PIN 2
#define STOP_BUTTON_PIN 4
#define RESET_BUTTON_PIN 5

// Variables to track stopwatch state and time
volatile bool stopwatchRunning = false;
volatile unsigned long startTime = 0;
volatile unsigned long elapsedTime = 0;

// Interrupt service routine for the start button
void startButtonISR() {
  if (!stopwatchRunning) {
    startTime = millis();
    stopwatchRunning = true;
  }
}

// Interrupt service routine for the stop button
void stopButtonISR() {
  if (stopwatchRunning) {
    elapsedTime = millis() - startTime;
    stopwatchRunning = false;
  }
}

// Interrupt service routine for the reset button
void resetButtonISR() {
  if (!stopwatchRunning) {
    elapsedTime = 0;
  }
}

void setup() {
  Serial.begin(9600);
  
  // Configure button pins as inputs with pull-up resistors
  pinMode(START_BUTTON_PIN, INPUT_PULLUP);
  pinMode(STOP_BUTTON_PIN, INPUT_PULLUP);
  pinMode(RESET_BUTTON_PIN, INPUT_PULLUP);
  
  // Attach interrupt service routines to the buttons
  attachInterrupt(digitalPinToInterrupt(START_BUTTON_PIN), startButtonISR, FALLING);
  attachInterrupt(digitalPinToInterrupt(STOP_BUTTON_PIN), stopButtonISR, FALLING);
  attachInterrupt(digitalPinToInterrupt(RESET_BUTTON_PIN), resetButtonISR, FALLING);
}

void loop() {
  if (stopwatchRunning) {
    unsigned long currentTime = millis();
    unsigned long displayTime = elapsedTime + (currentTime - startTime);
    
    // Display elapsed time
    Serial.print("Elapsed Time: ");
    Serial.print(displayTime / 1000); // Convert milliseconds to seconds
    Serial.println(" seconds");
  }
  
  delay(100); // Add a small delay to debounce buttons
}