#include <Preferences.h>

Preferences pf;

#define LED 11
#define btn 13

unsigned long runner = 0, curr = 0;
int STATE = 0;

void setup() {
  Serial.begin(115200);

  pinMode(LED, OUTPUT);
  pinMode(btn, INPUT);
  
  pf.begin("LED", true);
  STATE = pf.getInt("STATE", 0);
  Serial.printf("LED state read...");
  pf.end();
}

void loop() {
  runner = millis();
  
  if(runner - curr == 500)
  {
    curr = millis();
    toggleState();
    digitalWrite(LED, STATE);
  }

  int btnState = digitalRead(btn);

  if(btnState)
  {
    btnState = 0;
    Serial.println("Saving...");
    pf.begin("LED", false);
    pf.putInt("STATE", STATE);
    pf.end();
    Serial.println("Saved!");
  }
}

void toggleState()
{
  if(STATE == 0)
    STATE = 1;
  else
    STATE = 0;
}