#define SENSOR_PIN A3
#define RELAY_PIN 3

#define SENSOR_SAMPLE_COUNT 50
#define SENSOR_THRESHOLD 50
#define RELAY_SHUTOFF_DELAY 5000


bool RELAY_STATE = HIGH;
int INDEX = 0;
int SAMPLES[SENSOR_SAMPLE_COUNT] = {0};


int getMaxIntFromArray(int *arr, int len)
{
  int maxValue = 0;
  for (int i = 0; i < len; i++)
  {
    if (arr[i] > maxValue)
    {
      maxValue = arr[i];
    }
  }
  return maxValue;
}


int getSensorValue()
{
  for (int i = 0; i < SENSOR_SAMPLE_COUNT; i++)
  {
    INDEX = (INDEX + 1) % SENSOR_SAMPLE_COUNT;
    SAMPLES[INDEX] = abs(analogRead(SENSOR_PIN) - 512);
    delay(10);
  }
  return getMaxIntFromArray(SAMPLES, SENSOR_SAMPLE_COUNT);
}


void setup()
{
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, HIGH);
}


void loop()
{
  int sensorValue = getSensorValue();
  if (sensorValue < SENSOR_THRESHOLD)
  {
    if (RELAY_STATE == LOW)
    {
      delay(RELAY_SHUTOFF_DELAY);
      sensorValue = getSensorValue();
    }
    
    if (sensorValue < SENSOR_THRESHOLD)
    {
      // Vacuum off.
      RELAY_STATE = HIGH;
    }
  }
  else
  {
    // Vacuum on.
    RELAY_STATE = LOW;
  }
  digitalWrite(RELAY_PIN, RELAY_STATE);
}