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

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

/* Keypad setup */
const byte KEYPAD_ROWS = 4; // Represent number of rows and columns
const byte KEYPAD_COLS = 4;
byte rowPins[KEYPAD_ROWS] = {5, 4, 3, 2}; // Makes an array
byte colPins[KEYPAD_COLS] = {A3, A2, A1, A0}; // 

//rows and columns are switched. (j,i) format. 
//so below, (0,3) is 3rd row, 0th column.

char keys[KEYPAD_ROWS][KEYPAD_COLS] = { // 2D array showing layout of keypad
  {'1', '2', '3', '+'}, // Each element here is a button on the keypad.
  {'4', '5', '6', '-'}, // Ex, '+' is first row, 4th column of keypad = keys[0][3] which is A.
  {'7', '8', '9', '*'},
  {'C', '0', '=', '/'} // Inspired by Wokwi electronic safe design
};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, KEYPAD_ROWS, KEYPAD_COLS);
// Creates a Keypad object named keypad for use later.
// https://forum.arduino.cc/t/keypad-libary-question/553761  


long first = 0; //want longs to store lots of decimals for sig digs.
long second = 0;
long total = 0;
char key;
char index = 1;
bool resultsflag = false; 

void setup() {  // Inspired by Wokwo electronic safe
  lcd.begin(16, 2); //starts.
  lcd.print("Calculator");
  lcd.setCursor(0, 0);
  delay(2000); // Waits for 1000ms = 1 second
  lcd.clear(); // Clears after the 1 second.
}

void loop() {
  key = keypad.getKey(); // Reads key pressed.
  switch(key) 
  {

  case 'C': //want to have a clear case.
  total = 0;
  first = 0;
  second = 0;
  index = 1;
  lcd.clear();
  break;

  case '0' ... '9': //had to google the syntax to use. case 'thing' then colon.
    lcd.setCursor(0,0); // start in top left position.
    first = first * 10 + (key - '0'); //should allow for adding multiple concatenations.
    
    if (resultsflag) {
      lcd.clear();
      resultsflag = false; 
    }
    lcd.print(first);
    index += 1;

  break;

  case '+': //addition
    if (resultsflag) {
      lcd.clear();
      total = 0;
      first = 0;
      second = 0;
      index = 1;
      lcd.clear();
      resultsflag = false; 
    }
    if (total != 0) {
      first = total; } 
    else {
      first = first; }
    //lcd.setCursor(0,0);
    lcd.print("+"); //want to display the plus sign.
    second = SecondNumber();
    total = first + second; //does math.
    lcd.setCursor(0,3); //lowers cursor to next line.
    lcd.print(total);
    resultsflag = true;
    first = 0, second = 0; //clears values.

  break; //end case. 

  case '-': // subtraction
  if (resultsflag) {
      lcd.clear();
      total = 0;
      first = 0;
      second = 0;
      index = 1;
      lcd.clear();
      resultsflag = false; 
    }
    if (total != 0) {
      first = total; } 
    else {
      first = first; }
      //lcd.setCursor(1,0);
    lcd.print("-"); //want to display the - sign.
    second = SecondNumber();
    total = first - second; //does math. order of ops matters. first - second.
    lcd.setCursor(0,3); //lowers cursor to next line.
    lcd.print(total);
    resultsflag = true;

    first = 0, second = 0; //resets values.
  break; //end case. 


  case '*': //multiplication
  if (resultsflag) {
      lcd.clear();
      total = 0;
      first = 0;
      second = 0;
      index = 1;
      lcd.clear();
      resultsflag = false; 
    }
    if (total != 0) {
      first = total; } 
    else {
      first = first; }
      //lcd.setCursor(1,0);
    lcd.print("*"); //display the * sign.
    second = SecondNumber();
    total = first * second; //does multiplication
    lcd.setCursor(0,3); //lowers cursor to next line.
    lcd.print(total);
    resultsflag = true;

    first = 0, second = 0; //resets values.
  break; //end case. 

  case '/': //need to have special case for division by 0.
  if (resultsflag) {
      total = 0;
      first = 0;
      second = 0;
      index = 1;
      lcd.clear();
      resultsflag = false; 
    }
    if (total != 0) {
      first = total; } 
    else {
      first = first; }
    
    //lcd.setCursor(1,0);
    lcd.print("/"); //display the / sign.
    second = SecondNumber();
    lcd.setCursor(0,3); //lowers cursor to next line.


    if (second == 0) { //this will test for dividing by 0.
    lcd.print("Invalid: Division by 0"); 
    resultsflag = true; }

    else {
    total = first / second;
    }

    lcd.print(total);
      resultsflag = true;

    first = 0, second = 0; //resets values.
   break; //end case. 

  
}}

long SecondNumber()
{
  
  while (1) //while true
  {
    key = keypad.getKey(); //get input
    if (key >= '0' && key <= '9') //if a number. all other cases covered above.
    {
      second = second * 10 + (key - '0');
      lcd.setCursor(index,0); //puts 2nd number on top line, 3rd spot. so first number, room for 2nd.
      lcd.print(second); //print to screen. 
//so at this point, first is on line 1, second line 2, and operation line 3.
    }
    if (key == 'C'){
      total = 0;
      first = 0;
      second = 0;
      index = 1;
      lcd.clear();
      break;
    }

    if (key == '=') 
    break; //stop when equals sign is pressed.
  }
      return second;
}


//$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$//first attempt.

//   if (key != NO_KEY) { // For some reason you have to include this. Basically an if statement that says if a key is pressed.
//     // First step - get numbers. Want to make sure if multidigit, will concatenate into string.
//     if (key >= '0' && key <= '9') { // Getting digit between 0-9.
//       input += key; // Add digit to string. Accounts for multidigit numbers.
//       lcd.print(key); // Want to print it out. 
//     }
//     else if (key == '+' || key == '-' || key == '/' || key == '*') {
//       num1 = input.toInt();
//       operation = key; // Store the operation in a new variable.
//       lcd.clear(); // Clear the display before printing the operation
//       lcd.print(operation); // Display the operation sign
//     } else if (key == '=') {
//       num2 = input.toInt();
//       calculate(); // Perform calculation. Made a calculate function.
//     } else if (key == '.') {
//       input = ""; // Clear the input string
//       lcd.clear(); // Clear it. 
//     }
//   }
// }

// void calculate() {
//   int result; // Make new variable called result. 
//   if (operation == '+') {
//     result = num1 + num2;
//   } else if (operation == '-') {
//     result = num1 - num2;
//   } else if (operation == '*') {
//     result = num1 * num2;
//   } else if (operation == '/') {
//     if (num2 == 0) {
//       lcd.print("Error: Divide by 0"); // Display error message
//       delay(2000); // Wait for 2 seconds
//       lcd.clear(); // Clear the display
//       return;
//     } else {
//       result = num1 / num2;
//     }
//   }
//   lcd.print(result); // Display the result on LCD
// }