/**
  Arduino Calculator
  
  Description:
  This Arduino project implements a basic calculator using a LiquidCrystal display
  and a 4x4 keypad. It supports basic arithmetic operations: addition, subtraction,
  multiplication, and division.
*/

#include <LiquidCrystal.h> // Library for LCD display
#include <Keypad.h>        // Library for keypad input
#include <Servo.h>         // Library for servo control (included but not used in this code)

// -------------------- Hardware Configuration --------------------

// Initialize the LiquidCrystal library with the interface pins.
// (RS, E, D4, D5, D6, D7)
LiquidCrystal lcd(12, 11, 10, 9, 8, 7);

// Define the number of rows and columns for the keypad
const byte KEYPAD_ROWS = 4;
const byte KEYPAD_COLS = 4;

// Assign Arduino pins to the keypad rows and columns
byte rowPins[KEYPAD_ROWS] = {5, 4, 3, 2};       // Connect to the row pinouts of the keypad
byte colPins[KEYPAD_COLS] = {A3, A2, A1, A0};   // Connect to the column pinouts of the keypad

// Define the keys on the keypad
char keys[KEYPAD_ROWS][KEYPAD_COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'.', '0', '=', '/'}
};

// Initialize the Keypad library with the keymap and pin configuration
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, KEYPAD_ROWS, KEYPAD_COLS);

// -------------------- Global Variables --------------------

// Stores the first operand or the result
String memory = "";

// Stores the current input from the user
String current = "";

// Stores the selected arithmetic operation
char operation = 0;

// Flag to track if a decimal point has been entered
bool decimalPoint = false;

// -------------------- Function Definitions --------------------

/**
  Displays the splash screen with a welcome message and the word "Calculator".
  Each character of "Calculator" appears with a slight delay for a typing effect.
*/
void showSplashScreen() {
  lcd.print("Calculator");
  lcd.setCursor(3, 1);
  
  String message = "by hayooshkah";
  for (byte i = 0; i < message.length(); i++) {
    lcd.print(message[i]);
    delay(120); // Delay between each character
  }
  
  delay(500); // Wait before clearing the screen
}

/**
  Toggles the cursor visibility to create a blinking effect.
*/
void updateCursor() {
  // Blink the cursor every 250 milliseconds
  if ((millis() / 250) % 2 == 0) {
    lcd.cursor();    // Show cursor
  } else {
    lcd.noCursor();  // Hide cursor
  }
}

/**
  Performs the calculation based on the selected operation.
  
  @param operation The arithmetic operation ('+', '-', '*', '/')
  @param left The left operand
  @param right The right operand
  @return The result of the operation
*/
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) {
        return left / right;
      } else {
        lcd.clear();
        lcd.setCursor(0, 0);
        lcd.print("Error: Div 0");
        return 0;
      }
    default: return 0;
  }
}

/**
  Processes the input key pressed by the user.
  
  @param key The key character pressed
*/
void processInput(char key) {
  // Handle negative sign for the first number
  if (key == '-' && current == "") {
    current = "-";
    lcd.print("-");
    return;
  }

  switch (key) {
    // If an operation key is pressed
    case '+':
    case '-':
    case '*':
    case '/':
      if (operation == 0) { // If no operation is selected yet
        memory = current;    // Store the current input as the first operand
        current = "";        // Reset current input
      }
      operation = key;       // Set the selected operation
      lcd.setCursor(0, 1);   // Move cursor to the second line
      lcd.print(key);        // Display the operation
      lcd.setCursor(current.length() + 1, 1); // Move cursor after the operation
      return;

    // If the equals key is pressed
    case '=':
      if (operation != 0 && memory != "" && current != "") {
        double leftNum = memory.toDouble();   // Convert stored memory to double
        double rightNum = current.toDouble();  // Convert current input to double
        double result = calculate(operation, leftNum, rightNum); // Perform calculation
        memory = String(result);               // Store the result in memory
        current = "";                          // Reset current input
        lcd.clear();                           // Clear the display
        lcd.setCursor(1, 0);                   // Set cursor to the first line
        lcd.print(memory);                     // Display the result
        lcd.setCursor(0, 1);                   // Move cursor to the second line
        lcd.print(operation);                  // Display the operation
      }
      return;
  }

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

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

  lcd.print(key); // Display the pressed key
}

// -------------------- Arduino Setup and Loop --------------------

/**
  The setup function runs once when the Arduino starts.
  It initializes serial communication, the LCD, and displays the splash screen.
*/
void setup() {
  Serial.begin(115200); // Initialize serial communication for debugging (optional)
  
  lcd.begin(16, 2);     // Initialize the LCD with 16 columns and 2 rows
  showSplashScreen();   // Display the splash screen
  lcd.clear();          // Clear the LCD display
  lcd.cursor();         // Show the cursor
  lcd.setCursor(1, 0);  // Set cursor to the first line, second character
}

/**
  The loop function runs continuously after setup().
  It updates the cursor and checks for keypad input.
*/
void loop() {
  updateCursor(); // Update the cursor blinking

  char key = keypad.getKey(); // Get the pressed key from the keypad
  if (key) {                   // If a key is pressed
    processInput(key);         // Process the input
  }
}