// https://forum.arduino.cc/t/urgent-help-with-this-project-please-urgent/1408628/

// sensor activity adds (timeout) to enable relay
// more than (timeout) inactivity disables relay

byte pinSensor = 12;
byte pinRelay = 3,  pinBlu = 4, pinGrn = 5, pinRed = 6;
unsigned long timer, timeout = 1000, warning = 250;

void setup() {
  pinMode(pinSensor, INPUT_PULLUP);
  for (byte i = 0; i < 4; i++)
    pinMode(i + 3, OUTPUT);
  digitalWrite(pinRelay, LOW); // disable relay
  timer = millis() + timeout; // set new timer
}

void loop() {
  if (digitalRead(pinSensor) == 1) {
    if (timer - millis() > timeout) { // calculate duration
      digitalWrite(pinRelay, LOW); // disable relay
      indicate(HIGH, LOW, LOW); // red
    }
  }

  if (digitalRead(pinSensor) == 0) { // sensor active
    digitalWrite(pinRelay, HIGH); // enable relay
    timer = millis() + timeout; // set new timer
    indicate(LOW, HIGH, LOW); // grn
  }

  if (timer - millis() < warning) { // time ending
    indicate(LOW, LOW, HIGH); // blu
  }
}

void indicate (byte red, byte grn, byte blu) {
  digitalWrite(pinRed, red);
  digitalWrite(pinGrn, grn);
  digitalWrite(pinBlu, blu);
}