/**
   STM32 Calculator for Nucleo-C031C6

   Adapted from Arduino Calculator by Uri Shaked.
   Copyright (C) 2020, Uri Shaked.
   Released under the MIT License.
*/

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

/* Display (I2C-based 16x2 LCD) */
#define I2C_ADDR    0x27
LiquidCrystal_I2C lcd(I2C_ADDR, 16, 2);

/* Keypad setup */
const byte KEYPAD_ROWS = 4;
const byte KEYPAD_COLS = 4;
byte rowPins[KEYPAD_ROWS] = {D9, D10, D11, D12}; // Adjust based on Wokwi
byte colPins[KEYPAD_COLS] = {D13, D14, D15, D16}; // Adjust based on Wokwi
char keys[KEYPAD_ROWS][KEYPAD_COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'.', '0', '=', '/'}
};

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

/* LED Pins */
#define RED_LED   D5    // Red LED for errors
#define YELLOW_LED D6   // Yellow LED for operation input
#define GREEN_LED D7    // Green LED for result

/* Variables */
String memory = "";
String current = "";
char operation = 0;
bool decimalPoint = false;

void setLEDs(bool red, bool yellow, bool green) {
  digitalWrite(RED_LED, red ? HIGH : LOW);
  digitalWrite(YELLOW_LED, yellow ? HIGH : LOW);
  digitalWrite(GREEN_LED, green ? HIGH : LOW);
}

void pulseRed() {
  setLEDs(true, false, false);
  delay(100);
  setLEDs(false, false, false);
}

void showSplashScreen() {
  lcd.setCursor(0, 0);
  lcd.print("STM32 Calculator");
  lcd.setCursor(3, 1);
  String message = "Ready!";
  for (byte i = 0; i < message.length(); i++) {
    lcd.print(message[i]);
    delay(50);
  }
  delay(500);
}

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

double calculate(char operation, double left, double right) {
  switch (operation) {
    case '+': return left + right;
    case '-': return left - right;
    case '*': return left * right;
    case '/':
      if (right == 0) {
        pulseRed();
        return 0; // Handle division by zero
      }
      return left / right;
  }
  return 0;
}

void processInput(char key) {
  // Handle negative numbers at the start
  if (key == '-' && current == "") {
    current = "-";
    lcd.print("-");
    return;
  }

  switch (key) {
    case '+':
    case '-':
    case '*':
    case '/':
      if (!operation) {
        memory = current;
        current = "";
      }
      operation = key;
      lcd.setCursor(0, 1);
      lcd.print(key);
      lcd.setCursor(current.length() + 1, 1);
      setLEDs(false, true, false); // Yellow LED for operation
      return;

    case '=':
      if (memory == "" || current == "") {
        pulseRed();
        return;
      }
      double leftNum = memory.toDouble();
      double rightNum = current.toDouble();
      double result = calculate(operation, leftNum, rightNum);
      memory = String(result);
      current = "";
      lcd.clear();
      lcd.setCursor(0, 0);
      lcd.print(memory);
      lcd.setCursor(0, 1);
      lcd.print(operation);
      setLEDs(false, false, true); // Green LED for result
      return;
  }

  // Prevent multiple decimal points
  if (key == '.' && current.indexOf('.') >= 0) {
    pulseRed();
    return;
  }

  // Handle leading zero
  if (key != '.' && current == "0") {
    current = String(key);
  } else if (key) {
    current += String(key);
  }

  lcd.print(key);
}

void setup() {
  // Initialize Serial
  Serial.begin(115200);

  // Initialize LCD
  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.cursor();

  // Initialize LED pins
  pinMode(RED_LED, OUTPUT);
  pinMode(YELLOW_LED, OUTPUT);
  pinMode(GREEN_LED, OUTPUT);
  setLEDs(false, false, false);

  // Show splash screen
  showSplashScreen();
  lcd.clear();
  lcd.cursor();
  lcd.setCursor(1, 0);
}

void loop() {
  updateCursor();

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