#include <unistd.h>
#include <sys/types.h>
#include <sys/file.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>

struct plog_entry
{
    int mjd;	/* MJD at UTC midnight */
    int mod;	/* #minutes from UTC midnight */
    int ticks;	/* #ticks in the minute (10 ms) */
    int flags;	/* 5-bit flags */
    int lst;	/* local apparent sidereal time (10 ms) */
    int ra;	/* requested apparent right ascension (10 ms) */
    int dec;	/* requested apparent declination (100 mas) */
    int pa;	/* parallactic angle (100 mas) */
    int az;	/* requested azimuth (100 mas) */
    int el;	/* requested elevation (100 mas) */
    int eaz;	/* error in azimuth (100 mas) */
    int eel;	/* error in elevation (100 mas) */
};

#define PLOG_BASE_EPOCH	(51543)	/* MJD at 0 UTC, Jan. 0, 2000 */

#define PLOG_IS_TRACKING(x)	((x) & 0x10)
#define PLOG_IS_ACQUIRED(x)	((x) & 0x08)
#define PLOG_IS_SCANNING(x)	((x) & 0x04)
#define PLOG_IS_TRANSITED(x)	((x) & 0x02)
#define PLOG_IS_CELESTIAL(x)	((x) & 0x01)

int plog_read(int fd, struct plog_entry *pe)
{
    unsigned char b[30];
    int n;

    if ((n = read(fd, b, 30)) != 30)
    {
	if (n == -1)
	{
	    perror("read");
	    return errno;
	}

	return EOF;
    }

    pe->mjd = PLOG_BASE_EPOCH + (b[2] << 6) + (b[3] >> 2);
    pe->mod = ((b[3] & 0x3) << 9) + (b[4] << 1) + ((b[5] & 0x80) >> 7);
    pe->ticks = ((b[0] & 0x1f) << 8) + b[1];
    pe->flags = (b[5] & 0x7c) >> 2;
    pe->lst = (b[6] << 16) + (b[7] << 8) + b[8];
    if (b[6] & 0x80)	/* extend sign bit */
    {
	pe->lst |= 0xff000000;
	pe->lst += 8640000;
    }
    pe->ra = (b[9] << 16) + (b[10] << 8) + b[11];
    if (b[9] & 0x80)	/* extend sign bit */
    {
	pe->ra |= 0xff000000;
	pe->ra += 8640000;
    }
    pe->dec = (b[12] << 15) + (b[13] << 7) + ((b[14] & 0xfe) >> 1);
    if (b[12] & 0x80)	/* extend sign bit */
	pe->dec |= 0xff800000;
    pe->pa = ((b[14] & 0x1) << 23) + (b[15] << 15) + (b[16] << 7)
	+ ((b[17] & 0xfe) >> 1);
    if (b[14] & 0x1)	/* extend sign bit */
	pe->pa |= 0xff000000;
    pe->az = ((b[17] & 0x1) << 24) + (b[18] << 16) + (b[19] << 8) + b[20];
    if (b[17] & 0x1)	/* extend sign bit */
	pe->az |= 0xfe000000;
    pe->el = (b[21] << 15) + (b[22] << 7) + ((b[23] & 0xfe) >> 1);
    if (b[21] & 0x80)	/* extend sign bit */
	pe->el |= 0xff800000;
    pe->eaz = ((b[23] & 0x1) << 24) + (b[24] << 16) + (b[25] << 8) + b[26];
    if (b[23] & 0x1)	/* extend sign bit */
	pe->eaz |= 0xfe000000;
    pe->eel = (b[27] << 16) + (b[28] << 8) + b[29];
    if (b[27] & 0x80)	/* extend sign bit */
	pe->eel |= 0xff000000;

    return 0;
}

int main()
{
    struct plog_entry entry;

    fputs("MJD   Time (s) flags LST (hr)  R.A.(hr)  Dec.(deg) P.A.(deg)  "
	  "Az.(deg)   El.(deg)  Az.Err.(\") El.Err.(\")\n", stdout);

    while (plog_read(0, &entry) == 0)
    {
	printf("%5d %8.2f %c%c%c%c%c "
	       "%9.6f %9.6f %+9.5f %+10.5f %+10.5f %+9.5f %+10.1f %+10.1f\n",
	       entry.mjd,
	       (double) entry.mod * 60.0 + (double) entry.ticks / 100.0,
	       PLOG_IS_TRACKING(entry.flags) ? '1' : '0',
	       PLOG_IS_ACQUIRED(entry.flags) ? '1' : '0',
	       PLOG_IS_SCANNING(entry.flags) ? '1' : '0',
	       PLOG_IS_TRANSITED(entry.flags) ? '1' : '0',
	       PLOG_IS_CELESTIAL(entry.flags) ? '1' : '0',
	       (double) entry.lst / 360000.0,
	       (double) entry.ra / 360000.0, (double) entry.dec / 36000.0,
	       (double) entry.pa / 36000.0,
	       (double) entry.az / 36000.0, (double) entry.el / 36000.0,
	       (double) entry.eaz / 10.0, (double) entry.eel / 10.0);
    }

    return 0;
}