// Digit control pins
#define DIGIT_1 4
#define DIGIT_2 5
#define DIGIT_3 6
#define DIGIT_4 15

// Segment pins
#define SEG_A 7
#define SEG_B 9
#define SEG_C 13
#define SEG_D 11
#define SEG_E 10
#define SEG_F 8
#define SEG_G 14
#define SEG_DP 12

// Store pins in arrays for easy access
int digitPins[4]   = {DIGIT_1, DIGIT_2, DIGIT_3, DIGIT_4};
int segmentPins[8] = {SEG_A, SEG_B, SEG_C, SEG_D, SEG_E, SEG_F, SEG_G, SEG_DP};


const byte digitPatterns[10][8] = {
  {0,0,0,0,0,0,1,1}, // 0
  {1,0,0,1,1,1,1,1}, // 1
  {0,0,1,0,0,1,0,1}, // 2
  {0,0,0,0,1,1,0,1}, // 3
  {1,0,0,1,1,0,0,1}, // 4
  {0,1,0,0,1,0,0,1}, // 5
  {0,1,0,0,0,0,0,1}, // 6
  {0,0,0,1,1,1,1,1}, // 7
  {0,0,0,0,0,0,0,1}, // 8
  {0,0,0,0,1,0,0,1}  // 9
};

int displayBuffer[4] = {1, 2, 3, 4};  // initial content
int currentDigit = 0;
unsigned long lastUpdate = 0;
unsigned long lastCounterUpdate = 0;
int counter = 0;

void setup() {
  // Set digit pins as outputs
  for (int i = 0; i < 4; i++) {
    pinMode(digitPins[i], OUTPUT);
    digitalWrite(digitPins[i], LOW); 
  }
  // Set segment pins as outputs
  for (int i = 0; i < 8; i++) {
    pinMode(segmentPins[i], OUTPUT);
    digitalWrite(segmentPins[i], HIGH); // all segments OFF (HIGH = OFF)
  }
}

void loop() {
  unsigned long now = millis();

  // Refresh display
  if (now - lastUpdate >= 5) {
    // Turn off all digits
    for (int i = 0; i < 4; i++) digitalWrite(digitPins[i], LOW);

    // Set segment states for current digit
    int num = displayBuffer[currentDigit];
    for (int s = 0; s < 8; s++) {
      digitalWrite(segmentPins[s], digitPatterns[num][s]);
    }

    // Enable the current digit (HIGH = ON for common anode)
    digitalWrite(digitPins[currentDigit], HIGH);

    // Move to next digit
    currentDigit = (currentDigit + 1) % 4;
    lastUpdate = now;
  }

  // Update counter every second
  if (now - lastCounterUpdate >= 1000) {
    counter++;
    if (counter > 9999) counter = 0;

    displayBuffer[0] = counter / 1000;
    displayBuffer[1] = (counter / 100) % 10;
    displayBuffer[2] = (counter / 10) % 10;
    displayBuffer[3] = counter % 10;

    lastCounterUpdate = now;
  }
}