#include <LiquidCrystal_I2C.h>

const int IO_PINS[] = {12, 11, 10, 9, 8, 7};
const int BTN_CTRL_PINS[] = {5, 4};
const int BTN_IN_PIN = 6;
const int NUM_BTNS = 2;

int btnState[NUM_BTNS];
int oldBtnState[NUM_BTNS] = {1, 1};

LiquidCrystal_I2C lcd(0x27, 16, 2);

int checkButtons()  {
  int btnNumber = 0;

  for (int i = 0; i < NUM_BTNS; i++) {
    // check each button
    btnState[i] = digitalRead(BTN_CTRL_PINS[i]);
    if (btnState[i] != oldBtnState[i])  { // if it changed
      oldBtnState[i] = btnState[i];       // remember state for next time
      btnNumber = i + 1;
      Serial.print("Button ");
      Serial.print(btnNumber);
      if (btnState[i] == LOW)  {          // was just pressed
        Serial.println(" pressed.");
      } else {
        btnNumber = -1;                   // was just released
        Serial.println(" released.");
      }
      delay(20);  // debounce
    }
  }
  return btnNumber;
}

void showSplash() {
  lcd.setCursor(5, 0);
  lcd.print("Hello");
  lcd.setCursor(5, 1);
  lcd.print("world!");
  delay(2000);
  lcd.clear();
}

void setup() {
  Serial.begin(115200);
  lcd.init();
  lcd.backlight();
  for (int i = 0; i < 6; i++) {
    pinMode(IO_PINS[i], OUTPUT);
  }
  pinMode(BTN_CTRL_PINS[0], INPUT_PULLUP);
  pinMode(BTN_CTRL_PINS[1], INPUT_PULLUP);
  pinMode(BTN_IN_PIN, INPUT);
  showSplash();
}

void loop() {
  bool flag = false;
  int btnNumber = checkButtons();
  for (int i = 0; i < 6; i++) {
    digitalWrite(IO_PINS[i], HIGH);
    if (digitalRead(BTN_IN_PIN) == HIGH)  {
      flag = true;
      lcd.setCursor(5, 1);
      lcd.print(i);
    }
    digitalWrite(IO_PINS[i], LOW);
    delay(50);
  }
  if (!flag) lcd.clear();
}