#include <Keypad.h>
/* Display */
#include <LiquidCrystal_I2C.h>
//Crear el objeto lcd  dirección  0x3F y 16 columnas x 2 filas
LiquidCrystal_I2C lcd(0x27,16,2); 

/* Keypad setup */
const byte KEYPAD_ROWS = 4;
const byte KEYPAD_COLS = 4;
byte rowPins[KEYPAD_ROWS] = {5, 4, 3, 2};
byte colPins[KEYPAD_COLS] = {6,7,8,9};
char keys[KEYPAD_ROWS][KEYPAD_COLS] = {
  {'7', '8', '9', '/'},
  {'4', '5', '6', 'X'},
  {'1', '2', '3', '-'},
  {'0', 'C', '=', '+'}
};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, KEYPAD_ROWS, KEYPAD_COLS);

uint64_t value = 0;

void setup() {
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0, 0);
}

char operation = 0;
String memory = "";
bool equal_press = false;
String current = "";


double calculate(char operation, double left, double right) { // calcular resultado 
  switch (operation) {
    case '+': return left + right;
    case '-': return left - right;
    case 'X': return left * right;
    case '/': return left / right;
  }
}
void result(){ // obtencionde los numeros e imperesion an pantalla
  
  float leftNum = memory.toDouble();
  float rightNum = current.toDouble();
  memory = String(calculate(operation, leftNum, rightNum));
  current = "";
  lcd.setCursor(0, 1);
  lcd.print(memory);
  lcd.setCursor(0,0);
}
void processInput(char key) {

  switch (key) { // posibles teclas
    case '+':
    case '-':
    case 'X':
    case '/':
      if (!operation) {
        memory = current;
      }
      else{
        if(equal_press){ // si se ha presionado el igual
          lcd.clear();
          lcd.setCursor(0, 1);
          lcd.print(memory);
          lcd.setCursor(0,0);
          lcd.print("Ans");
        }
        else{ // sino hacer la operion
          lcd.clear();
          result();
          lcd.print("Ans");
        }
      }
      current = "";
      operation = key;
      lcd.print(key);// escribir signo
      equal_press = false;
      return;
    case '=':
      result();
      equal_press = true;
      return;
    case 'C': //borrar todo y poner por defecto
      char operation = 0;
      String memory = "";
      String current = "";
      equal_press = false;
      lcd.clear();
      return;
  }
  current += key; //añadir digito
  lcd.print(key); //escribir numero
}
void loop() {
  char key = keypad.getKey(); 
  if (key) { // si se presiona una tecla
    processInput(key);
  }
}