#include <Arduino.h>

#define NUM_RELAYS 4
#define INTERVAL 4 // Time in seconds
#define DELAY_INTERVAL 2
const byte relayPin[NUM_RELAYS] = {4, 7, 8, 12};

bool currentStatus[NUM_RELAYS] = {false};
unsigned long prevMillis = 0;
unsigned long delayMillis = 0;

byte relaysChanged = 0;

void printDebug(byte i, bool ln = false)
{
  digitalWrite(relayPin[i], currentStatus[i]);
  Serial.print("Relay ");
  Serial.print(i);
  Serial.println(currentStatus[i] ? ": ON" : ": OFF");

  if(ln == true)
  {
    Serial.println();
  }
}
void setup()
{
  Serial.begin(9600);

  for (byte i = 0; i < NUM_RELAYS; i++)
  {
    pinMode(relayPin[i], OUTPUT);
    printDebug(i);
  }
  Serial.println();
  prevMillis = millis();
}

void loop()
{
  if ((millis() - prevMillis) >= (INTERVAL * 1000UL))
  {
    for (byte i = 0; i < NUM_RELAYS; i++)
    {
      if (i != (NUM_RELAYS - 1))
      {
        currentStatus[i] = !currentStatus[i];
        digitalWrite(relayPin[i], currentStatus[i]);

        if (currentStatus[i] == true)
        {
          relaysChanged++;
        }
        
        printDebug(i);
      }
    }

    if (relaysChanged == 0)
    {
      currentStatus[NUM_RELAYS - 1] = false;
      digitalWrite(relayPin[NUM_RELAYS - 1], currentStatus[NUM_RELAYS - 1]);

      printDebug(NUM_RELAYS - 1, true);
    }
    prevMillis = millis();
    delayMillis = millis();
  }

  if (relaysChanged == (NUM_RELAYS - 1))
  {
    if ((millis() - delayMillis) >= (DELAY_INTERVAL * 1000UL))
    {
      currentStatus[NUM_RELAYS - 1] = true;
      digitalWrite(relayPin[NUM_RELAYS - 1], currentStatus[NUM_RELAYS - 1]);

      printDebug(NUM_RELAYS - 1, true);

      relaysChanged = 0;
    }
  }
}