#include <Wire.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);

// define variables
String txtMsg = "Arduino";
int i, j;

unsigned long previousMillis = 0;
const long interval = 50;
const long holdInterval = 5000;

enum State {
  MOVE_CHAR_IN,
  MOVE_CHAR_OUT,
  WAIT_BETWEEN_CHARS,
  HOLD_DISPLAY
};

State currentState = MOVE_CHAR_IN;

void setup() {
  lcd.init();
  lcd.clear();
  lcd.backlight();

  i = txtMsg.length() - 1;  // start from last character
  j = 0;  // start from first LCD position
}

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

  switch (currentState) {
    case MOVE_CHAR_IN:
      if (currentMillis - previousMillis >= interval) {
        lcd.setCursor(j, 1);
        lcd.print(txtMsg[i]);
        if (j > 0) {
          lcd.setCursor(j - 1, 1);
          lcd.print(' ');
        }
        j++;
        previousMillis = currentMillis;

        if (j == i + 2) {
          currentState = WAIT_BETWEEN_CHARS;
        }
      }
      break;

    case WAIT_BETWEEN_CHARS:
      if (currentMillis - previousMillis >= interval) {
        i--;
        j = 0;
        previousMillis = currentMillis;

        if (i < 0) {
          currentState = HOLD_DISPLAY;
        } else {
          currentState = MOVE_CHAR_IN;
        }
      }
      break;

    case HOLD_DISPLAY:
      if (currentMillis - previousMillis >= holdInterval) {
        i = txtMsg.length() - 1;
        j = 0;
        previousMillis = currentMillis;
        lcd.clear();
        currentState = MOVE_CHAR_OUT;
      }
      break;

    case MOVE_CHAR_OUT:
      if (currentMillis - previousMillis >= interval) {
        previousMillis = currentMillis;
        lcd.setCursor(i, 1);
        lcd.print(txtMsg[i - 1]);
        if (j > 0) {
          j--;
          lcd.setCursor(j, 1);
          lcd.print(' ');
        }
        else {
          lcd.setCursor(0, 1);
          lcd.print("                ");  // Clear line
          currentState = MOVE_CHAR_IN;
        }
      }
      break;
  }
}