# include <time.h>

struct tm firstTime;
struct tm todayTime;

time_t baseTime;
time_t codeTime;

void setup()
{
  mySetup();
  printf("\nhello world.\n");

  test();
}

void loop()
{
}

int test()
{
    printf("Hello World ");
    
/*
  9/21/22 4067	0173
  9/22/22	4239	0172


 10/10/22 7349	0173
*/
    
    
    int baseCode = 4239;
    firstTime.tm_year = 2022 - 1900;
    firstTime.tm_mon = 9 - 1; // 22 september 2022
    firstTime.tm_mday = 22;
    firstTime.tm_hour = 12;
    firstTime.tm_min = 0;
    firstTime.tm_sec = 1;
    firstTime.tm_isdst = -1;
    if (mktime(&firstTime) == -1)
        printf("-unknown-");

    baseTime = mktime(&firstTime);
    
    todayTime.tm_year = 2022 - 1900;
    todayTime.tm_mon = 10 - 1;  // 10 october 2022
    todayTime.tm_mday = 10;
    todayTime.tm_hour = 12;
    todayTime.tm_min = 0;
    todayTime.tm_sec = 1;
    todayTime.tm_isdst = -1;
    if (mktime(&todayTime) == -1)
        printf("-unknown-");
        
    codeTime = mktime(&todayTime);
        
    printf("%ld %ld %ld %ld\n", baseTime, codeTime, codeTime - baseTime, (codeTime - baseTime) / 86400L);
    
    int daysSince = (codeTime - baseTime) / 86400L;
 
    int roller = 0;
    int newCode = baseCode;
    
    for (int dd = 0; dd < daysSince; dd++) {
// add 173 three times and 172 once
        if (roller < 3) newCode += 173;
        else newCode += 172;
        
// poor man's modulo 10000
        if (newCode >= 10000) newCode -= 10000;

        roller++; roller &= 0x3;
    }

    printf("\n\n new code %d\n", newCode);

    return 0;
}

# include <stdio.h>

int serial_putc(char c, FILE *)
{
  Serial.write(c);

  return c;
}

void printf_begin(void)
{
  fdevopen(&serial_putc, 0);
}

void mySetup()
{
  Serial.begin(115200);

  printf_begin(); 
}