#include <LiquidCrystal.h>
#include <Keypad.h>

/* Display */
LiquidCrystal x(12, 11, 10, 9, 8, 7);

/* Keypad setup */
const byte X_ROWS = 4;
const byte X_COLS = 4;
byte rowPins[X_ROWS] = {5, 4, 3, 2};
byte colPins[X_COLS] = {A3, A2, A1, A0};
char keys[X_ROWS][X_COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'.', '0', '=', '/'}
};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, X_ROWS, X_COLS);

uint64_t value = 0;

void showRandomScreen() {
  x.print("Welcome");
  x.setCursor(0, 1);
  String message = "Calculator";
  for (byte i = 0; i < message.length(); i++) {
    x.print(message[i]);
    delay(50);
  }
  delay(500);
}

void updateRandom() {
  if (millis() / 250 % 2 == 0 ) {
    x.cursor();
  } else {
    x.noCursor();
  }
}

void setup() {
  Serial.begin(115200);
  x.begin(16, 2);

  showRandomScreen();
  x.clear();
  x.cursor();

  x.setCursor(1, 0);
}

char randomOp = 0;
String store = "";
String randomVal = "";
uint64_t randomDecimal;
bool randomPoint = false;

double processRandom(char randomOp, double left, double right) {
  switch (randomOp) {
    case '+': return left + right;
    case '-': return left - right;
    case '*': return left * right;
    case '/': return left / right;
  }
}

void randomInput(char key) {
  if ('-' == key && randomVal == "") {
    randomVal = "-";
    x.print("-");
    return;
  }

  switch (key) {
    case '+':
    case '-':
    case '*':
    case '/':
      if (!randomOp) {
        store = randomVal;
        randomVal = "";
      }
      randomOp = key;
      x.setCursor(0, 1);
      x.print(key);
      x.setCursor(randomVal.length() + 1, 1);
      return;

    case '=':
      float leftNum = store.toDouble();
      float rightNum = randomVal.toDouble();
      store = String(processRandom(randomOp, leftNum, rightNum));
      randomVal = "";
      x.clear();
      x.setCursor(1, 0);
      x.print(store);
      x.setCursor(0, 1);
      x.print(randomOp);
      return;
  }

  if ('.' == key && randomVal.indexOf('.') >= 0) {
    return;
  }

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

  x.print(key);
}

void loop() {
  updateRandom();

  char key = keypad.getKey();
  if (key) {
    randomInput(key);
  }
}