// Pin definitions
int digit1 = 9; // Display d1
int digit2 = 10; // Display d2
int digit3 = 11; // Display d3
int digit4 = 12; // Display d4
int segA = 1; // Display pin a
int segB = 2; // Display pin b
int segC = 3; // Display pin c
int segD = 4; // Display pin d
int segE = 5; // Display pin e
int segF = 6; // Display pin f
int segG = 7; // Display pin g
int count = 9999; // Start counter at 9999
unsigned long previousMillis = 0; // Store the last update time
const long interval = 1000; // Interval at which to decrement (1 second)

void setup() {
  pinMode(segA, OUTPUT);
  pinMode(segB, OUTPUT);
  pinMode(segC, OUTPUT);
  pinMode(segD, OUTPUT);
  pinMode(segE, OUTPUT);
  pinMode(segF, OUTPUT);
  pinMode(segG, OUTPUT);
  pinMode(digit1, OUTPUT);
  pinMode(digit2, OUTPUT);
  pinMode(digit3, OUTPUT);
  pinMode(digit4, OUTPUT);
}

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

  // Decrement count every second
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis; // Save the last update time
    count--;
    
    // Reset count to 9999 if it goes below 0
    if (count < 0) {
      count = 9999;
    }
  }

  // Display the current count
  displayNumber(count);
}

void displayNumber(int toDisplay) {
  #define DISPLAY_BRIGHTNESS 1000
  #define DIGIT_ON HIGH
  #define DIGIT_OFF LOW
  long beginTime = millis();
  for (int digit = 4; digit > 0; digit--) {
    switch (digit) {
      case 1:
        digitalWrite(digit1, DIGIT_ON);
        break;
      case 2:
        digitalWrite(digit2, DIGIT_ON);
        break;
      case 3:
        digitalWrite(digit3, DIGIT_ON);
        break;
      case 4:
        digitalWrite(digit4, DIGIT_ON);
        break;
    }
    lightNumber(toDisplay % 10);
    toDisplay = toDisplay / 10;
    delayMicroseconds(DISPLAY_BRIGHTNESS);
    lightNumber(10); // Turn off segments
    digitalWrite(digit1, DIGIT_OFF);
    digitalWrite(digit2, DIGIT_OFF);
    digitalWrite(digit3, DIGIT_OFF);
    digitalWrite(digit4, DIGIT_OFF);
  }
  while ((millis() - beginTime) < 10);
}

void lightNumber(int numberToDisplay) {
  #define SEGMENT_ON LOW
  #define SEGMENT_OFF HIGH
  switch (numberToDisplay) {
    case 0:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_ON);
      digitalWrite(segE, SEGMENT_ON);
      digitalWrite(segF, SEGMENT_ON);
      digitalWrite(segG, SEGMENT_OFF);
      break;
    case 1:
      digitalWrite(segA, SEGMENT_OFF);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_OFF);
      digitalWrite(segE, SEGMENT_OFF);
      digitalWrite(segF, SEGMENT_OFF);
      digitalWrite(segG, SEGMENT_OFF);
      break;
    case 2:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_OFF);
      digitalWrite(segD, SEGMENT_ON);
      digitalWrite(segE, SEGMENT_ON);
      digitalWrite(segF, SEGMENT_OFF);
      digitalWrite(segG, SEGMENT_ON);
      break;
    case 3:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_ON);
      digitalWrite(segE, SEGMENT_OFF);
      digitalWrite(segF, SEGMENT_OFF);
      digitalWrite(segG, SEGMENT_ON);
      break;
    case 4:
      digitalWrite(segA, SEGMENT_OFF);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_OFF);
      digitalWrite(segE, SEGMENT_OFF);
      digitalWrite(segF, SEGMENT_ON);
      digitalWrite(segG, SEGMENT_ON);
      break;
    case 5:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_OFF);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_ON);
      digitalWrite(segE, SEGMENT_OFF);
      digitalWrite(segF, SEGMENT_ON);
      digitalWrite(segG, SEGMENT_ON);
      break;
    case 6:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_OFF);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_ON);
      digitalWrite(segE, SEGMENT_ON);
      digitalWrite(segF, SEGMENT_ON);
      digitalWrite(segG, SEGMENT_ON);
      break;
    case 7:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_OFF);
      digitalWrite(segE, SEGMENT_OFF);
      digitalWrite(segF, SEGMENT_OFF);
      digitalWrite(segG, SEGMENT_OFF);
      break;
    case 8:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_ON);
      digitalWrite(segE, SEGMENT_ON);
      digitalWrite(segF, SEGMENT_ON);
      digitalWrite(segG, SEGMENT_ON);
      break;
    case 9:
      digitalWrite(segA, SEGMENT_ON);
      digitalWrite(segB, SEGMENT_ON);
      digitalWrite(segC, SEGMENT_ON);
      digitalWrite(segD, SEGMENT_ON);
      digitalWrite(segE, SEGMENT_OFF);
      digitalWrite(segF, SEGMENT_ON);
      digitalWrite(segG, SEGMENT_ON);
      break;
    case 10:
      digitalWrite(segA, SEGMENT_OFF);
      digitalWrite(segB, SEGMENT_OFF);
      digitalWrite(segC, SEGMENT_OFF);
      digitalWrite(segD, SEGMENT_OFF);
      digitalWrite(segE, SEGMENT_OFF);
      digitalWrite(segF, SEGMENT_OFF);
      digitalWrite(segG, SEGMENT_OFF);
      break;
  }
}