#define HAND_SENSOR PB0
#define TRIG_PIN    PA1
#define ECHO_PIN    PA0
#define PUMP_PIN    PB1
#define LOW_LED     PB12
#define LED         PB10

// Adjust after testing your container
const float LOW_LEVEL_DISTANCE = 12.0;

bool previousHandState = false;

float readDistanceCM() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);

  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  unsigned long duration =
      pulseIn(ECHO_PIN, HIGH, 30000UL);

  if (duration == 0) {
    return -1.0;  // Invalid reading
  }

  return duration * 0.0343 / 2.0;
}

void setup() {
  pinMode(HAND_SENSOR, INPUT_PULLUP);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(PUMP_PIN, OUTPUT);
  pinMode(LOW_LED, OUTPUT);

  digitalWrite(PUMP_PIN, LOW);
  digitalWrite(LOW_LED, LOW);

  Serial.begin(115200);
  Serial.println("Smart Handwash Dispenser Ready");
}

void loop() {
  bool handDetected =
      (digitalRead(HAND_SENSOR) == LOW);

  float distance = readDistanceCM();

  // Invalid readings must not permit dispensing.
  bool sensorValid = (distance >= 2.0);
  bool lowLiquid =
      (!sensorValid ||
       distance >= LOW_LEVEL_DISTANCE);

  digitalWrite(LOW_LED, lowLiquid ? HIGH : LOW);

  if (sensorValid) {
    Serial.print("Liquid distance: ");
    Serial.print(distance);
    Serial.println(" cm");
  } else {
    Serial.println("Ultrasonic reading invalid");
  }

  // Dispense once for each new hand detection.
  if (handDetected &&
      !previousHandState &&
      !lowLiquid) {

    Serial.println("Hand detected: dispensing");

    digitalWrite(PUMP_PIN, HIGH);
    delay(700);
    digitalWrite(PUMP_PIN, LOW);

    Serial.println("Dispensing complete");
  }

  if (lowLiquid) {
    Serial.println("LOW LIQUID: Refill required");
  }

  previousHandState = handDetected;
  delay(100);
}