#define LED LED_BUILTIN // digital pin connected to LED, for testing of switch code only
bool led_status = LOW;  // start with LED off, for testing of switch code only

int button_switch = 2; // external interrupt pin

#define SWITCHED true  // value if the button switch has been pressed
#define TRIGGERED true // controls interrupt handler
#define INTERRUPT_TRIGGER_TYPE RISING // interrupt triggered on a RISING input
#define DEBOUNCE 20 // time to wait in milliseconds

volatile bool interrupt_process_status = !TRIGGERED; // start with no switch press pending, ie false (!triggered)
bool initialisation_complete = false; // inhibit any interrupts until initialisation is complete

void button_interrupt_handler() {
  if (initialisation_complete && interrupt_process_status == !TRIGGERED) {
    if (digitalRead(button_switch) == HIGH) {
      interrupt_process_status = TRIGGERED;
    }
  }
}

bool read_button() {
  static bool switching_pending = false;
  static unsigned long elapse_timer;

  if (interrupt_process_status == TRIGGERED) {
    int button_reading = digitalRead(button_switch);
    if (button_reading == HIGH) {
      switching_pending = true;
      elapse_timer = millis();
    }
    if (switching_pending && button_reading == LOW) {
      if (millis() - elapse_timer >= DEBOUNCE) {
        switching_pending = false;
        interrupt_process_status = !TRIGGERED;
        return SWITCHED;
      }
    }
  }
  return !SWITCHED;
}

void setup() {
  pinMode(LED, OUTPUT);
  pinMode(7, OUTPUT); // for testing
  pinMode(button_switch, INPUT);
  attachInterrupt(digitalPinToInterrupt(button_switch), button_interrupt_handler, INTERRUPT_TRIGGER_TYPE);
  initialisation_complete = true;
}

void loop() {
  if (read_button() == SWITCHED) {
    led_status = !led_status;
    digitalWrite(LED, led_status);
  } else {
    digitalWrite(7, HIGH);  // turn the LED on (HIGH is the voltage level)
    delay(1000);            // wait for a second
    digitalWrite(7, LOW);   // turn the LED off by making the voltage LOW
    delay(1000);            // wait for a second
  }
}