#include <EEPROM.h>
  
  const int EEPROM_DELAY_FACTOR_ADDR = 0;
  const int EEPROM_IS_DELAY_DECREASING_ADDR = 1;
  
  const int IS_DELAY_DECREASING = 0;
  const int IS_DELAY_INCREASING = 1;

  // the setup function runs once when you press reset or power the board
  void setup() {
    // initialize digital pin LED_BUILTIN as an output.
    pinMode(LED_BUILTIN, OUTPUT);

    if (EEPROM.read(EEPROM_DELAY_FACTOR_ADDR) == 255) {
        EEPROM.update(EEPROM_DELAY_FACTOR_ADDR, 1);
    }
    if (EEPROM.read(EEPROM_IS_DELAY_DECREASING_ADDR) == 255) {
        EEPROM.update(EEPROM_IS_DELAY_DECREASING_ADDR, IS_DELAY_DECREASING);
    }
  }

  // the loop function runs over and over again forever
  void loop() {
    int storedDelayFactor = EEPROM.read(EEPROM_DELAY_FACTOR_ADDR);
    double delayFactor = 1 + (double)storedDelayFactor / 2;

    bool isDelayDecreasing = EEPROM.read(EEPROM_IS_DELAY_DECREASING_ADDR) == IS_DELAY_DECREASING;

    int currentDelay = 1000 / delayFactor;
    digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(currentDelay);                       // wait for a second
    digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
    delay(currentDelay);

    if (currentDelay >= 1000) {
        EEPROM.update(EEPROM_IS_DELAY_DECREASING_ADDR, IS_DELAY_DECREASING);
        isDelayDecreasing = true;
    } else if (currentDelay <= 100) {
        EEPROM.update(EEPROM_IS_DELAY_DECREASING_ADDR, IS_DELAY_INCREASING);
        isDelayDecreasing = false;
    }
    
    if (isDelayDecreasing) {
        EEPROM.update(EEPROM_DELAY_FACTOR_ADDR, storedDelayFactor + 1);
    } else {
        EEPROM.update(EEPROM_DELAY_FACTOR_ADDR, storedDelayFactor - 1);
    }
  }