/*
References
https://www.arduino.cc/reference/en/language/functions/external-interrupts/attachinterrupt/
https://youtu.be/CNiWWX15Zns
https://docs.wokwi.com/parts/wokwi-lcd1602
https://docs.wokwi.com/parts/wokwi-membrane-keypad
https://create.arduino.cc/projecthub/123samridhgarg/arduino-calculator-bb57c7
https://docs.wokwi.com/parts/wokwi-pushbutton
https://wokwi.com/arduino/libraries/demo/simon-game
https://wokwi.com/projects/288681423014986248











*/
#include <LiquidCrystal.h>
#include <Keypad.h>
#include <avr/wdt.h>
#include <EEPROM.h>
const byte ROWS = 4;
const byte COLUMNS = 4;
const byte BUTTON_PIN = 19;



String memory = "";
String memory2 = "";

char process = 0;
int lastState = HIGH;

// mapping the keys
//source https://docs.wokwi.com/parts/wokwi-membrane-keypad

char keys[ROWS][COLUMNS] = {
{'1','2','3','+'},
{'4','5','6','-'},
{'7','8','9','*'},
{'.','0','=','/'}};


// connect keypad with columns and rows with arduino
byte rowPins[ROWS] = { 15, 16, 17, 18 };
byte colPins[COLUMNS] = {A3, A2, A1, A0 };


//makinng keypad
Keypad K = Keypad(makeKeymap(keys),rowPins,colPins,ROWS,COLUMNS);

// Assign LCD with the pins
const int rs=12;
const int en=11;
const int d4=10;
const int d5=9;
const int d6=8;
const int d7=7; 
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

long Num1,Num2,Number;
char key,action;
boolean result = false;


void setup()
{
  lcd.clear();
  //Serial.begin(115200);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  //digitalWrite(BUTTON_PIN,LOW);
  lcd.begin(16, 2);
  lcd.setCursor(0, 1);
  lcd.clear();
  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), DetectButtons, HIGH);
  
}



double CalculateResult(char process, double number1, double number2) 
{
  switch (process) {                   // using switch instead of if-else to shorten
    case '+': return number1 + number2;
    case '-': return number1 - number2;
    case '*': return number1 * number2;
    case '/': return number1 / number2;
  }
}



void operation(char key) {
    if ('-' == key && memory2 == "") {
      memory2 = "-";
      lcd.print("-");
      return;
    }

  switch (key) {
    case '+':
    case '-':
    case '*':
    case '/':
      if (!process) {
        memory = memory2;
        memory2 = "";
      }
      process = key;
      lcd.setCursor(0, 1);
      lcd.print(key);
      lcd.setCursor(memory2.length() + 1, 1);
      return;

    case '=':
      float Number1 = memory.toDouble();      //converting to floting point
      float Number2 = memory2.toDouble();
      memory = String(CalculateResult(process, Number1, Number2));
      memory2 = "";
      lcd.clear();
      lcd.setCursor(1, 0);
      lcd.print(memory);
      lcd.setCursor(0, 1);
      lcd.print(process);
      return;
  }
  
  if ('.' == key && memory2.indexOf('.') >= 0) 
  {
  return;
  }

  if ('.' != key && memory2 == "0") 
  {
    memory2 = String(key);
  } 
  else if (key) 
  {
    memory2 += String(key);
  }

  lcd.print(key);
}





void CursorBlink() {
  if (millis() / 250 % 2 == 0 ) {   //curser blinks every 1/4th seconds or 250 mili seconds
    lcd.cursor();
  } else {
    lcd.noCursor();
  }
}

void reboot() {
  wdt_disable();
  wdt_enable(WDTO_15MS);
  while (1) {}
}

void DetectButtons()
{
  /*
  int value = digitalRead((BUTTON_PIN));
  if (lastState != value) {
    lastState = value;
    if (value == HIGH) 
    {
      num = "";
      num2= "";
      Serial.println(" released");
    }
  } */
  memory = "";
  memory2 = "";
  Num1 = 0;
  Num2 = 0;
  Number = 0;
  key = 0;
  action = 0;
  lcd.clear();
  

  //Serial.end();


}


/*
void loop()
{
  CursorBlink();

  key =K.getKey();

    if (key!=NO_KEY)
      DetectButtons();

    if (key)
    {
      result = true;
//      CalculateResult();
      operation(key);
    }

}

void setWDT ()
{
  WDTCSR |= 0b00011000;
  WDTCSR = sWDT | WDTO_1S;
  wdt_reset();
}
ISR (WDT_vect) 
{
  digitalWrite(led, HIGH); 
  if(wSetting == 3) {
    byte b = 1;
    EEPROM.put(10, b);
  }
  //wdt_disable();
}
*/


void loop() {
  
  CursorBlink();
  char key = K.getKey();
  if (key) {
    operation(key);
    }
}