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

LiquidCrystal_I2C lcd(0x27, 16, 2);
boolean State = false;
const byte ROWS = 4;
const byte COLS = 4;
const byte MAX_IDX = 14;
const byte MIN_IDX = 1;
unsigned long time = 0;
int current_index = 0;
String Buffer = "";
boolean blink = true;
boolean equal = false;


//keypad define
char hexaKeys[ROWS][COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', 'x'},
  {'C', '0', '.', '='}
};
//LCD define
byte customChar[8] = {
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111
};

byte customChar1[8] = {
  0b00011,
  0b00111,
  0b01111,
  0b11111,
  0b11111,
  0b01111,
  0b00111,
  0b00011
};

byte rowPins[ROWS] = {31, 33, 35, 37};
byte colPins[COLS] = {39, 41, 43, 45};
Keypad customKeypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);

void Cursor(int Index) {
  // blink cursor
  if (State == true) {
    if (equal == false) {
      if ((unsigned long)(millis() - time) > 500) {
        time = millis();
        if (blink == true) {
          blink = false;
          if (Index > 15) {
            lcd.setCursor(15, 0);
            lcd.write(byte(0));
          }
          else {
            lcd.setCursor(Index, 0);
            lcd.write(byte(0));
          }
        }
        else {
          blink = true;
          if (Index > 15) {
            lcd.setCursor(15, 0);
            lcd.print(" ");
          }
          else {
            lcd.setCursor(Index, 0);
            lcd.print(" ");
          }
        }
      }
      else;
      if (Index > 15) {
        lcd.setCursor(0, 0);
        lcd.write(byte(1));
      }
    }
  }
  else {}
}

int calculate(String s) {
    // calculator algorithm using stack
    int len = s.length();
    if (len == 0) return 0;
    float stack[100] = {0, 0, 0, 0, 0};
    int curr = 0;
    float currentNumber = 0;
    char operation = '+';
    int dot = 0; // decimal detect
    for (int i = 0; i < len; i++) {
        char currentChar = s[i];
        if (currentChar == '.'){
          dot = 1; // finding "." to make decimal in form of 0.X, 0.00X
        } 
        else {
          if (isDigit(currentChar)) {
              // "." found, curren number = current number + X/10^x .
              // "." not found, current number = curent number*10 + X
              if (!dot) currentNumber = (currentNumber * 10); 
              currentNumber += (currentChar - '0') / pow(10,dot);
          }
          if (!isDigit(currentChar) || i == len - 1) {
              // 
              if (operation == '-') {
                  // stack.push(-currentNumber); extraction
                  stack[curr] = -currentNumber;
                  curr++;
              } else if (operation == '+') {
                  // stack.push(currentNumber); addition
                  stack[curr] = currentNumber;
                  curr++;
              } else if (operation == 'x') {
                  // stackTop = stack.pop();multiplication
                  curr--;
                  float stackTop = stack[curr];
                  // stack.push(stackTop * currentNumber);
                  stack[curr] = stackTop * currentNumber;
                  curr++;
              }
              operation = currentChar;
              currentNumber = 0;
          }
          dot = 0;
        }
    }
    float result = 0;
    while (curr-- != 0) {
        result += stack[curr];
    }

    if (result - int(result) == 0) {
      lcd.setCursor(16 - String(int(result)).length(), 1);
      lcd.print(int(result));
    }
    else {
      lcd.setCursor(16 - String(result).length(), 1);
      lcd.print(result);
    }
}



void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.createChar(0, customChar);
  lcd.createChar(1, customChar1);
  time = millis();
}
void reset(){
  lcd.clear();
  current_index = 0;
  Buffer = "";
  equal = false;
}
void turnOff(){
  reset();
  State = false;
  lcd.noBacklight();
}
void turnOn(){
  reset();
  State = true;
  lcd.backlight();
}
void loop() {
  Cursor(current_index);
  char customKey = customKeypad.getKey();
  if (customKey) {
    if (customKey == 'C') { // C=on off button
      if (State == false) turnOn();
       else turnOff();
    }
    else if ((customKey == '=') && State) { // =: do the math with related operator
      // if turn on & key =
      equal = true;
      calculate(Buffer);
    }
    else if (State && equal) reset(); // reset lcd after "=" and to next calculation
    else if (State) { // else number/operator
        Buffer = Buffer + String(customKey); // Update number/operator to String
        lcd.setCursor(min(current_index,MAX_IDX), 0); // Move cursor to last position
        lcd.print(Buffer.substring(current_index, Buffer.length() + 1)); //display input from start to end
        current_index++; // Move cursor to the next position
    }
  }
}