#include <SPI.h>

// Define pin numbers for buttons and LEDs
const int decrementButtonPin = 2;    // Pin connected to the decrement button
const int resetButtonPin = 3;        // Pin connected to the reset button
const int greenLEDPin = 4;           // Pin connected to the green LED
const int redLEDPin = 5;             // Pin connected to the red LED

// Define pins for shift register control
const int latchPin = 6;    // Connects to RCLK on the first 74HC595
const int clockPin = 7;    // Connects to SRCLK on both 74HC595
const int dataPin = 8;     // Connects to SER on the first 74HC595

// Define starting number for the counter
int counter = 24;

// Variables to store the last time the buttons were pressed
unsigned long lastDecrementTime = 0;
unsigned long lastResetTime = 0;

// Minimum time between button presses (milliseconds)
unsigned long debounceDelay = 200; // Adjusted debounce delay

// Variables to store the previous state of the buttons
bool lastDecrementButtonState = HIGH;
bool lastResetButtonState = HIGH;

// Define inverted patterns for displaying digits 0-9 on 7-segment displays
const byte digitPatterns[] = {
  B00000011,  // 0
  B10011111,  // 1
  B00100101,  // 2
  B00001100,  // 3
  B10011000,  // 4
  B01001001,  // 5
  B01000000,  // 6
  B00011110,  // 7
  B00000001,  // 8
  B00011001,  // 9
};

void setup() {
  // Initialize serial communication
  Serial.begin(9600);
  
  // Initialize inputs and outputs
  pinMode(decrementButtonPin, INPUT_PULLUP);
  pinMode(resetButtonPin, INPUT_PULLUP);
  pinMode(greenLEDPin, OUTPUT);
  pinMode(redLEDPin, OUTPUT);
  
  // Initialize shift register control pins
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  
  // Initially turn on the green LED
  digitalWrite(greenLEDPin, HIGH);
  digitalWrite(redLEDPin, LOW);
  
  // Initialize display
  updateDisplay(counter);
}

void loop() {
  handleDecrementButton();
  handleResetButton();
}

void handleDecrementButton() {
  bool currentDecrementButtonState = digitalRead(decrementButtonPin);
  
  // Check for the transition from HIGH to LOW
  if (currentDecrementButtonState == LOW && lastDecrementButtonState == HIGH) {
    if (millis() - lastDecrementTime >= debounceDelay) {
      lastDecrementTime = millis();
      if (counter > 0) {
        counter--;
        if (counter == 0) {
          // Turn off green LED and turn on red LED
          digitalWrite(greenLEDPin, LOW);
          digitalWrite(redLEDPin, HIGH);
        }
        // Update the display
        updateDisplay(counter);
      }
    }
  }

  // Update the last state
  lastDecrementButtonState = currentDecrementButtonState;
}

void handleResetButton() {
  bool currentResetButtonState = digitalRead(resetButtonPin);
  
  // Check for the transition from HIGH to LOW
  if (currentResetButtonState == LOW && lastResetButtonState == HIGH) {
    if (millis() - lastResetTime >= debounceDelay) {
      lastResetTime = millis();
      counter = 24;
      // Turn on green LED and turn off red LED
      digitalWrite(greenLEDPin, HIGH);
      digitalWrite(redLEDPin, LOW);
      // Update the display
      updateDisplay(counter);
    }
  }

  // Update the last state
  lastResetButtonState = currentResetButtonState;
}

void updateDisplay(int num) {
  // Extract digits from the number
  int tens = num / 10;
  int ones = num % 10;
  
  // Update the display using shift registers
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, LSBFIRST, digitPatterns[ones]);  // Shift out ones first
  shiftOut(dataPin, clockPin, LSBFIRST, digitPatterns[tens]);  // Shift out tens second
  digitalWrite(latchPin, HIGH);
}