#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 20, 4);

// RTC variables
char Time[9];       // hh:mm:ss
char DateLine[21];  // date string
byte second, minute, hour, day, date, month, year;

// HC-SR04 pins
const int trigPin = 9;
const int echoPin = 10;

// Backlight and timing
bool lcdBacklight = true;
unsigned long lastPresenceTime = 0;
const unsigned long absenceTimeout = 10000;  // 10 seconds
const int presenceThreshold = 95;            // in cm

// Buffer per aggiornamento parziale
char oldTime[9] = "        ";    // 8 spazi + terminatore
char oldDate[21] = "                    ";  // 20 spazi + terminatore

void setup() {
  Wire.begin();
  lcd.init();
  lcd.backlight();

  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  lcd.setCursor(0, 0);
  lcd.print("Starting...");
  delay(1000);
  lcd.clear();

  drawFrame(); // Disegna la cornice una volta sola
}

void loop() {
  unsigned long currentMillis = millis();

  int distance = readDistance();

  // Presenza rilevata
  if (distance > 0 && distance < presenceThreshold) {
    lastPresenceTime = currentMillis;

    if (!lcdBacklight) {
      lcd.display();
      lcd.backlight();
      lcdBacklight = true;
      drawFrame(); // ridisegna la cornice se si riaccende
      // Reset buffer per riaggiornare tutto subito
      memset(oldTime, ' ', sizeof(oldTime) - 1);
      oldTime[8] = '\0';
      memset(oldDate, ' ', sizeof(oldDate) - 1);
      oldDate[20] = '\0';
    }

  } else {
    // Nessuna presenza da oltre timeout
    if (lcdBacklight && (currentMillis - lastPresenceTime > absenceTimeout)) {
      lcd.noBacklight();
      delay(5000);
      lcd.noDisplay();
      lcdBacklight = false;
    }
  }

  if (lcdBacklight) {
    DS3231_read();
    updateTimeDate(); // aggiorna solo le parti variabili
  }

  delay(500);
}

// Leggi distanza in cm dall’HC-SR04
int readDistance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

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

  long duration = pulseIn(echoPin, HIGH, 30000); // timeout 30ms ~ 5m max

  if (duration == 0) return -1;  // nessuna lettura valida

  int distance = duration * 0.034 / 2; // distanza in cm
  return distance;
}

// Converti da BCD a decimale
byte bcdToDec(byte val) {
  return (val >> 4) * 10 + (val & 0x0F);
}

// Leggi da RTC DS3231
void DS3231_read() {
  Wire.beginTransmission(0x68);
  Wire.write(0);
  Wire.endTransmission(false);
  Wire.requestFrom(0x68, 7);

  second = bcdToDec(Wire.read());
  minute = bcdToDec(Wire.read());
  hour   = bcdToDec(Wire.read());
  day    = bcdToDec(Wire.read());
  date   = bcdToDec(Wire.read());
  month  = bcdToDec(Wire.read());
  year   = bcdToDec(Wire.read());
}

// Disegna cornice sul display LCD 20x4 (solo una volta)
void drawFrame() {
  lcd.setCursor(0, 0);
  lcd.print("+------------------+");

  for (int row = 1; row < 3; row++) {
    lcd.setCursor(0, row);
    lcd.print("|                  |");
  }

  lcd.setCursor(0, 3);
  lcd.print("+------------------+");
}

// Aggiorna solo i caratteri variati di ora e data centrati
void updateTimeDate() {
  sprintf(Time, "%02d:%02d:%02d", hour, minute, second);
  sprintf(DateLine, "%02d/%02d/20%02d", date, month, year);

  // Colonne di partenza per centrare
  const int timeStartCol = (20 - 8) / 2;   // 6
  const int dateStartCol = (20 - 10) / 2;  // 5

  // Aggiorna ora carattere per carattere sulla riga 1
  for (int i = 0; i < 8; i++) {
    if (Time[i] != oldTime[i]) {
      lcd.setCursor(timeStartCol + i, 1);
      lcd.print(Time[i]);
      oldTime[i] = Time[i];
    }
  }

  // Aggiorna data carattere per carattere sulla riga 2
  for (int i = 0; i < 10; i++) {
    if (DateLine[i] != oldDate[i]) {
      lcd.setCursor(dateStartCol + i, 2);
      lcd.print(DateLine[i]);
      oldDate[i] = DateLine[i];
    }
  }
}