const unsigned long LED1_DELAY = 3000; // Delay for LED 1
const unsigned long LED2_DELAY = 3000; // Delay for LED 2

unsigned long previousMillis1 = 0; //store the previous time when the LEDs were turned on
unsigned long previousMillis2 = 0; //store the previous time when the LEDs were turned on

bool led1State = LOW; //store the state of LED 1 and LED 2
bool led2State = LOW; 

const int led1Pin = 12; // store the pins that the LEDs and buttons are connected to
const int led2Pin = 13;
const int button1Pin = 3;
const int button2Pin = 2;

volatile int button1Pressed = LOW; //variables that store whether button 1 and button 2 are pressed
volatile int button2Pressed = LOW;

void setup() {
  Serial.begin(9600); 
  pinMode(led1Pin, OUTPUT); //set as OUTPUT
  pinMode(led2Pin, OUTPUT); //set as OUTPUT
  pinMode(button1Pin, INPUT_PULLUP); 
  pinMode(button2Pin, INPUT_PULLUP);

  // Attach interrupts to buttons
  attachInterrupt(digitalPinToInterrupt(button1Pin), button1ISR, FALLING); //interrupt on LED 1
  attachInterrupt(digitalPinToInterrupt(button2Pin), button2ISR, FALLING); //interrupt on LED 2
}

void loop() {   
  unsigned long currentMillis = millis();
 
  // if the buttonPressed variable is true it will turn on the corresponding LED 
  if (button1Pressed) { 
    if (!led1State && (currentMillis - previousMillis1) > LED1_DELAY) {  //enough time has elapsed since the last state change for LED 1
      led1State = true;
      digitalWrite(led1Pin, HIGH);
      previousMillis1 = currentMillis;
    }
    //when releasing the button, the buttonPressed variable is set back to false
    button1Pressed = LOW;
  } else {
    led1State = false;
    digitalWrite(led1Pin, LOW);
  }

  if (button2Pressed) {
    if (!led2State && (currentMillis - previousMillis2) > LED2_DELAY) { //enough time has elapsed since the last state change for LED 2
      led2State = true;
      digitalWrite(led2Pin, HIGH);
      previousMillis2 = currentMillis;
    }
    //when releasing the button, the buttonPressed variable is set back to false
    button2Pressed = LOW;
  } else {
    led2State = LOW;
    digitalWrite(led2Pin, LOW);
  }
}

void button1ISR() {
  button1Pressed = true; 
}

void button2ISR() {
  button2Pressed = true;
}