// ================= Configuration Variables =================
const int pirSensorPin = 23;          // PIR sensor GPIO pin
const int relay1Pin = 16;             // Relay GPIO pin
const unsigned long relayOnTimeMs = 4000; // Relay ON duration in milliseconds (4 seconds)

// ================= Internal State Variables =================
bool relayActive = false;
unsigned long relayStartTime = 0;

// ================= Function Prototypes =================
void handlePirAndRelay();

/*
 * Function: handlePirAndRelay
 * I/O: Reads PIR sensor (input), controls relay (output)
 * Working: Turns ON relay for a fixed time when PIR detects motion
 */
void handlePirAndRelay() {
  int pirState = digitalRead(pirSensorPin);

  // Error handling: ensure PIR read is valid
  if (pirState != HIGH && pirState != LOW) {
    digitalWrite(relay1Pin, LOW);
    relayActive = false;
    return;
  }

  // If motion detected and relay is not already active
  if (pirState == HIGH && !relayActive) {
    digitalWrite(relay1Pin, HIGH);
    relayActive = true;
    relayStartTime = millis();
  }

  // Turn OFF relay after specified time
  if (relayActive && (millis() - relayStartTime >= relayOnTimeMs)) {
    digitalWrite(relay1Pin, LOW);
    relayActive = false;
  }
}

void setup() {
  pinMode(pirSensorPin, INPUT);
  pinMode(relay1Pin, OUTPUT);

  // Ensure relay is OFF at startup
  digitalWrite(relay1Pin, LOW);
}

void loop() {
  handlePirAndRelay();
}