// Define pins for shift register
const int dataPin = 2;    // DS pin
const int clockPin = 3;   // SHCP pin
const int latchPin = 4;   // STCP pin

// Define pins for LEDs
const int led1Pin = 5;
const int led2Pin = 6;

// Define 7-segment digit patterns for common anode display
// For common anode: 0 = segment ON, 1 = segment OFF
// Bit positions: DP(MSB), G, F, E, D, C, B, A(LSB)
const byte digitPatterns[10] = {
  0b11000000,  // 0: segments A-F ON
  0b11111001,  // 1: segments B-C ON
  0b10100100,  // 2: segments A, B, D, E, G ON
  0b10110000,  // 3: segments A, B, C, D, G ON
  0b10011001,  // 4: segments B, C, F, G ON
  0b10010010,  // 5: segments A, C, D, F, G ON
  0b10000010,  // 6: segments A, C, D, E, F, G ON
  0b11111000,  // 7: segments A, B, C ON
  0b10000000,  // 8: all segments A-G ON
  0b10010000   // 9: segments A, B, C, D, F, G ON
};

// Variables for timing control
unsigned long previousLedTime = 0;
unsigned long previousCountdownTime = 0;
const long ledInterval = 2000;      // 2 seconds for LED toggle
const long countdownInterval = 4000; // 4 seconds for countdown

// State variables
int currentDigit = 9;       // Start countdown from 9
bool led1State = false;     // Both LEDs start OFF
bool led2State = false;

void setup() {
  // Initialize shift register pins
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
  
  // Initialize LED pins
  pinMode(led1Pin, OUTPUT);
  pinMode(led2Pin, OUTPUT);
  
  // Set initial LED states (both OFF)
  digitalWrite(led1Pin, LOW);
  digitalWrite(led2Pin, LOW);
  
  // Set initial 7-segment display to show "9"
  updateDisplay(currentDigit);
}

void loop() {
  unsigned long currentTime = millis();
  
  // Check if it's time to update the LED states
  if (currentTime - previousLedTime >= ledInterval) {
    previousLedTime = currentTime;
    
    // Special case for initial state where both LEDs are OFF
    if (led1State == false && led2State == false) {
      // First LED transition: LED1 ON, LED2 OFF
      led1State = true;
    } else {
      // Toggle LED states to ensure alternating pattern
      led1State = !led1State;
      led2State = !led2State;
    }
    
    // Update physical LEDs
    digitalWrite(led1Pin, led1State);
    digitalWrite(led2Pin, led2State);
  }
  
  // Check if it's time to update the countdown
  if (currentTime - previousCountdownTime >= countdownInterval) {
    previousCountdownTime = currentTime;
    
    // Decrement the current digit
    currentDigit--;
    
    // If we've reached below 0, reset to 9
    if (currentDigit < 0) {
      currentDigit = 9;
    }
    
    // Update the 7-segment display
    updateDisplay(currentDigit);
  }
}

// Function to update the 7-segment display through the shift register
void updateDisplay(int digit) {
  // Get the pattern for the current digit
  byte pattern = digitPatterns[digit];
  
  // Send the pattern to the shift register
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, pattern);
  digitalWrite(latchPin, HIGH);
}