#include <Arduino.h>

// Pin definitions for the shift register (74HC595)
const int dsPin = 26;   // Serial data input
const int shcpPin = 27; // Shift register clock input
const int stcpPin = 28; // Storage register (latch) clock input

// Digital pins for buttons and LED
const int btnIncrementPin = 24; // Connected to btn1 (using one terminal; other is GND)
const int btnDecrementPin = 25; // Connected to btn2 (using one terminal; other is GND)
const int ledPin = 29;

// Debounce delay in milliseconds
const unsigned long debounceDelay = 150;

// Lookup table for digits 0-9 for a common anode 7-seg display.
// For common anode, a LOW (0) turns on the segment.
// Patterns are arranged as: DP G F E D C B A   (bit7 to bit0)
// Standard patterns: 0=0xC0, 1=0xF9, 2=0xA4, 3=0xB0, 4=0x99,
//                    5=0x92, 6=0x82, 7=0xF8, 8=0x80, 9=0x90.
const byte digitPatterns[10] = {
  0xC0, // 0
  0xF9, // 1
  0xA4, // 2
  0xB0, // 3
  0x99, // 4
  0x92, // 5
  0x82, // 6
  0xF8, // 7
  0x80, // 8
  0x90  // 9
};

int currentDigit = 0;

void updateDisplay(byte pattern) {
  // Latch low to start shifting new data
  digitalWrite(stcpPin, LOW);
  // Use shiftOut to send the byte to the shift register.
  // Using MSBFIRST so that Q7 (DP) gets the MSB.
  shiftOut(dsPin, shcpPin, MSBFIRST, pattern);
  // Latch high to update outputs.
  digitalWrite(stcpPin, HIGH);
}

void updateLED(int digit) {
  // Turn on LED if digit is even, off if odd.
  if(digit % 2 == 0) {
    digitalWrite(ledPin, HIGH);
  } else {
    digitalWrite(ledPin, LOW);
  }
}

void setup() {
  // Setup shift register control pins
  pinMode(dsPin, OUTPUT);
  pinMode(shcpPin, OUTPUT);
  pinMode(stcpPin, OUTPUT);
  
  // Setup LED pin
  pinMode(ledPin, OUTPUT);
  
  // Setup pushbutton pins; use built-in pullup: button press reads LOW.
  pinMode(btnIncrementPin, INPUT_PULLUP);
  pinMode(btnDecrementPin, INPUT_PULLUP);
  
  // Initialize display with digit 0 and update LED accordingly.
  currentDigit = 0;
  updateDisplay(digitPatterns[currentDigit]);
  updateLED(currentDigit);
}

void loop() {
  // Check if the increment button is pressed (active low).
  if(digitalRead(btnIncrementPin) == LOW) {
    delay(debounceDelay); // Debounce delay
    // Wait for the button to be released to avoid multiple triggers.
    while(digitalRead(btnIncrementPin) == LOW) { }
    
    // Increment and wrap-around if greater than 9.
    currentDigit++;
    if(currentDigit > 9) {
      currentDigit = 0;
    }
    updateDisplay(digitPatterns[currentDigit]);
    updateLED(currentDigit);
  }
  
  // Check if the decrement button is pressed (active low).
  if(digitalRead(btnDecrementPin) == LOW) {
    delay(debounceDelay); // Debounce delay
    // Wait for the button to be released to avoid multiple triggers.
    while(digitalRead(btnDecrementPin) == LOW) { }
    
    // Decrement and wrap-around if less than 0.
    currentDigit--;
    if(currentDigit < 0) {
      currentDigit = 9;
    }
    updateDisplay(digitPatterns[currentDigit]);
    updateLED(currentDigit);
  }
  
  // Optional small delay to ensure loop stability.
  delay(10);
}