#include <Wire.h>
#include <PCF8574.h>
#include <RTClib.h>

RTC_DS1307 rtc;
PCF8574 pcfSeg(0x20);  // Segments
PCF8574 pcfDig(0x21);  // Digits

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

void setup() {
  Wire.begin();
  rtc.begin();

  pcfSeg.begin();
  pcfDig.begin();

  // Ensure all digit lines off
  for (int i = 0; i < 6; i++) pcfDig.write(i, 1);
}

void displayDigit(int digitIndex, int number) {
  // Turn OFF all digits
  for (int i = 0; i < 6; i++) pcfDig.write(i, 1);

  // Set segment bits for this digit
  for (int s = 0; s < 7; s++) {
    pcfSeg.write(s, digits[number][s]);
  }

  // Enable selected digit (active LOW)
  pcfDig.write(digitIndex, 0);
  delay(2); // Short display
  pcfDig.write(digitIndex, 1); // Turn OFF again
}

void loop() {
  DateTime now = rtc.now();

  int h = now.hour();
  int m = now.minute();
  int s = now.second();

  int displayValues[6] = {
    h / 10, h % 10,
    m / 10, m % 10,
    s / 10, s % 10
  };

  // Refresh whole display quickly (simulate persistence of vision)
  for (int i = 0; i < 6; i++) {
    displayDigit(i, displayValues[i]);
  }
}