//
// mjdclock - live MJD clock display.
//

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define WIN32_LEAN_AND_MEAN 
#include <windows.h>

void main (int argc, char *argv[])
{
    int dp, mode;
    char cr;
    char *ztime (SYSTEMTIME *st);
    long DateToMjd (long Year, long Month, long Day);

    // Set MJD decimal places.

    dp = (argc > 1) ? atoi(argv[1]) : 6;
    dp = min(dp, 9);
    dp = max(dp, 0);

    // Set display mode.

    mode = (argc > 2) ? atoi(argv[2]) : 1;
    cr = (mode >= 0) ? '\r' : '\n';

    // Display fractional MJD continuously.

    while (1) {
        double fMjd, secs;
        SYSTEMTIME St;
        time_t t;

        do {
            time(&t);
            GetSystemTime(&St);
        } while (St.wSecond != (t % 60));

        secs = (St.wHour * 60 + St.wMinute) * 60 + St.wSecond;
        secs += St.wMilliseconds / 1000.0;
        fMjd = DateToMjd(St.wYear, St.wMonth, St.wDay) + (secs / 86400.0);

        switch (abs(mode)) {
        default :
        case 1 :
            printf("%.*lf%c", dp, fMjd, cr);
            break;

        case 2 :
            printf("%.24s = %.*lf%c", ctime(&t), dp, fMjd, cr);
            break;

        case 3 :
            printf("%.24s = %s = %.*lf%c", ctime(&t), ztime(&St), dp, fMjd, cr);
            break;
        }
        _sleep(100); // milliseconds
    }
}

// Convert calendar date to MJD.

long DateToMjd (long Year, long Month, long Day)
{
    return
        367 * Year
        - 7 * (Year + (Month + 9) / 12) / 4
        - 3 * ((Year + (Month - 9) / 7) / 100 + 1) / 4
        + 275 * Month / 9
        + Day
        + 1721028
        - 2400000;
}

// Like ctime() except UTC with milliseconds.

char *ztime (SYSTEMTIME *st)
{
    static char buf[40]; // STATIC

    sprintf(buf, "%.4d-%.2d-%.2d %.2d:%.2d:%.2d.%.3d",
            st->wYear, st->wMonth, st->wDay,
            st->wHour, st->wMinute, st->wSecond,
            st->wMilliseconds);
    return buf; // STATIC
}