#include <Bounce2.h>

#define NUM_RELAYS 3
#define INITIAL_STATE LOW  // Initial state = HIGH to active LOW relay model.

struct INFOS
{
  const byte relayPin;
  bool relayState;
  const byte buttonPin;
};

INFOS info[NUM_RELAYS] =
{
  {2, INITIAL_STATE, 18}, // Relay 0 pin, relay 0 state, button 0 pin
  {4, INITIAL_STATE, 19},
  {5, INITIAL_STATE, 21}
};

Bounce2::Button button[NUM_RELAYS] = {Bounce2::Button()};

void printDebug(byte i)
{
  Serial.print("Button ");
  Serial.print(i);
  Serial.print(" pressed, relayState ");
  Serial.print(i);
  Serial.print(": ");
  Serial.println(info[i].relayState);
}

void setup()
{
  Serial.begin(9600);

  for (byte i = 0; i < NUM_RELAYS; i++)
  {
    button[i].attach(info[i].buttonPin, INPUT_PULLUP);
    button[i].setPressedState(LOW);
    button[i].interval(5);

    pinMode(info[i].relayPin, OUTPUT);
    digitalWrite(info[i].relayPin, info[i].relayState);
  }
}

void loop()
{
  for (byte i = 0; i < NUM_RELAYS; i++)
  {
    button[i].update();

    if (button[i].pressed())
    {
      info[i].relayState = !info[i].relayState;
      digitalWrite(info[i].relayPin, info[i].relayState);
      printDebug(i);
      break;
    }
  }
}