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

// Setup LCD display (address, columns, rows)
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Define push button pin
const int buttonPin = 1;

// Setup keypad matrix
#define ROWS 4
#define COLS 4
char keys[ROWS][COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'.', '0', '=', '/'}
};
byte rowPins[ROWS] = {5, 4, 3, 2};
byte colPins[COLS] = {A3, A2, A1, A0};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

// Function prototypes
void calculator();
void timer();

// Interrupt service routine 
void modeSwitch() { 
  static bool mode = 0; // 0 = calculator, 1 = timer
  mode = !mode;
  lcd.clear();

  if (mode) { 
    timer();  
  } else {
    calculator(); 
  }
}

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();

    // Attach interrupt to pin D1
  attachInterrupt(digitalPinToInterrupt(buttonPin), modeSwitch, RISING);
  sei(); // Enable interrupts

  // Set up push button pin
  pinMode(buttonPin, INPUT_PULLUP); 

}

void loop() {
  
    char key = keypad.getKey();

  if (key) {
    switch (key) {
      case '1':
        // Calculator mode
        calculator();
        break;
      case '2':
        // Timer mode
        timer();
        break;
      default:
        break;
    }
  }

  // Read the state of the push button
  int buttonState = digitalRead(buttonPin);

  if (buttonState ==LOW) {
    // Button is pressed
    // Call modeSwitch() function to toggle between calculator and timer modes
    modeSwitch();
  }
}

void calculator() {
  lcd.setCursor(0, 0);
  lcd.print("Calculator Mode");

  char input[17] = "";
  char operation = '\0';
  float result;
  float num1, num2;

  while (true) {
    char key = keypad.getKey();
    if (key) {
      if (key == '.') {
        break;
      }

      if (isdigit(key) || key == '.') {
        strncat(input, &key, 1);
        lcd.setCursor(0, 1);
        lcd.print(input);
      } else if (strchr("+-*/", key)) {
        if (strlen(input) > 0 && operation == '\0') {
          // If an operand has been pressed for the first time,
          // store the current input as num1 and display it on the same line
          // as the operand.
          operation = key;
          num1 = atof(input);
          input[0] = '\0';
          lcd.setCursor(0, 1);
          lcd.print(num1);
          lcd.print(operation);
        } else if (strlen(input) > 0 && operation != '\0') {
          // If an operand has been pressed for the second time,
          // store the current input as num2, perform the calculation,
          // and display the result on the next line.
          num2 = atof(input);
          switch (operation) {
            case '+': result = num1 + num2; break;
            case '-': result = num1 - num2; break;
            case '*': result = num1 * num2; break;
            case '/': result = num1 / num2; break;
            default: break;
          }
          num1 = result;
          input[0] = '\0';
          lcd.setCursor(0, 1);
          lcd.print(num2);
          lcd.print(operation);
          lcd.setCursor(0, 0);
          lcd.print(result, 2);
        }
      } else if (key == '=') {
        // If the equal sign is pressed, perform the calculation and
        // display the result on the next line.
        num2 = atof(input);
        switch (operation) {
          case '+': result = num1 + num2; break;
          case '-': result = num1 - num2; break;
          case '*': result = num1 * num2; break;
          case '/': result = num1 / num2; break;
          default: break;
        }
        lcd.setCursor(0, 1);
        lcd.print("      ");
        lcd.setCursor(0, 1);
        lcd.print(result, 2);
        input[0] = '\0';
        operation = '\0';
      }
    }
  }
  lcd.clear();
}

volatile int remainingTime = 0;
volatile bool timerRunning = false;

void timerISR() {
  // Decrement the remaining time if the timer is running
  if (timerRunning) {
    remainingTime--;
  }
}

void timer() {
  timerRunning = false;
  lcd.setCursor(0, 0);
  lcd.print("Timer Mode");

  char input[17] = "";
  int duration = 0;

  while (true) {
    char key = keypad.getKey();
    if (key) {
      if (key == '.') {
        break;
      }

      if (isdigit(key)) {
        strncat(input, &key, 1);
        lcd.setCursor(0, 1);
        lcd.print(input);
        duration = atoi(input);
      } else if (key == '=') {
        // Start the timer
        timerRunning = true;
        remainingTime = duration;
        input[0] = '\0';
      }
    }

    // Display the remaining time
    lcd.setCursor(0, 1);
    lcd.print("      ");
    lcd.setCursor(0, 1);
    lcd.print(remainingTime);

    // Check if the timer has expired
    if (remainingTime <= 0) {
      timerRunning = false;
      // Reset the input and display a message
      input[0], '\0';
      lcd.setCursor(0, 1);
      lcd.print("Time's up!");
      delay(1000);
      lcd.clear();
    }
  }
}