// Dimas Atha Putra
// 230605110052

// Kalkulator two-term sederhana.
//
// A untuk tambah
// B untuk kurang
// C untuk kali
// D untuk bagi
// # untuk evaluasi
// * untuk reset
//
// Jika membuat ekspresi baru setelah evaluasi, baris jawaban akan berkedip,
// menandakan bahwa jawaban yang ada di baris itu adalah hasil evaluasi
// ekspresi sebelumnya, dan bukan yang sedang diketik. Dapat dikatakan juga:
// kalkulator sedang menunggu evaluasi

#include <LiquidCrystal_I2C.h>
#include <Keypad.h>

const byte ROWS = 4; 
const byte COLS = 4; 

char hexaKeys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

byte rowPins[ROWS] = {9, 8, 7, 6}; 
byte colPins[COLS] = {5, 4, 3, 2}; 

Keypad keypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS); 
LiquidCrystal_I2C lcd(0x27, 16, 2);

String expression = "";
String ans = "";
String num1 = "";
String num2 = "";
String output = "Ans:           0";
boolean calculated = false;
boolean waiting = true;
int operand = 0;
int type = 0;
int prev_type = 0;
int terms = 0;
int clock = 0;

void setup(){
  lcd.init();
  lcd.backlight();
  Serial.begin(9600);
  lcd.setCursor(0, 1);
  lcd.print(output);
}
  
void loop(){
  char key = keypad.getKey();

  clock++;
  if (waiting) {
    lcd.setCursor(0, 1);
    if ((clock / 20) % 2 == 0) {
      lcd.print("Ans:            ");
    } else {
      lcd.print(output);
    }
  }
  
  if (key){
    String k = "";
    switch (key) {
      case 'A': k = " + "; prev_type = type; type = 1; operand = 1; break;
      case 'B': k = " - "; prev_type = type; type = 1; operand = 2; break;
      case 'C': k = " * "; prev_type = type; type = 1; operand = 3; break;
      case 'D': k = " / "; prev_type = type; type = 1; operand = 4; break;
      default: k = key; prev_type = type; type = 0; break;
    }

    if (key != '#' && key != '*') {
      if (terms > 2 && type == 0) {terms = 2;}
      else if (prev_type != type) {
        terms++;
      }
      if (terms == 0 && type == 0) {num1 += k;}
      if (terms >= 1 && type == 0) {num2 += k;}

      if (terms <= 2) {
        if (calculated) {
          expression = "";
          lcd.setCursor(0, 0);
          lcd.print("                ");
          calculated = false;
          waiting = true;
        }
        expression += key != '*' ? k : "";
        lcd.setCursor(0, 0);
        String spaces = "";
        for (int i = 0; i < (16 - expression.length()); i++) {
          spaces += " ";
        }
        lcd.print(spaces);
        lcd.print(expression);
      }
    } else if (key != '*') {
      terms = 0;
      ans = "";
      switch (operand) {
        case 1: ans += num1.toInt() + num2.toInt(); break;
        case 2: ans += num1.toInt() - num2.toInt(); break;
        case 3: ans += num1.toInt() * num2.toInt(); break;
        case 4: ans += num1.toDouble() / num2.toDouble(); break;
      }
      num1 = "";
      num2 = "";
      int ans_len = ans.length();
      String spaces = "";
      for (int i = 0; i < (12 - ans_len); i++) {
        spaces += " ";
      }
      
      output = ("Ans:") + spaces + ans;
      lcd.setCursor(0, 1);
      lcd.print(output);
      calculated = true;
      waiting = false;
    } else {
      lcd.clear();
      terms = 0;
      num1 = "";
      num2 = "";
      expression = "";
      lcd.setCursor(0, 1);
      lcd.print("Ans:           0");
    }
  }
}