//
// mjdsed - Replace "ctime" strings with MJD time stamps and prepend MJD to all lines.
//
// 24 Mar 2008 /tvb
//

#include <assert.h>
#include <ctype.h>
#include <memory.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

int ctime_like (char *s);
double ctime_to_mjd (char *s);

//
// Read stdin, substitude any ctime strings with MJD time stamps, write stdout.
//

void main (int argc, char *argv[])
{
    long count;
    char line[1000], *p;
    char buf[24 + 1];
    double mjd;

    count = 0;
    mjd = 0.0;
    while (fgets(line, sizeof line, stdin) != NULL) {

        // Extract date/time from line and set new MJD.
        for (p = line; p <= line + strlen(line); p += 1) {
            if (ctime_like(p)) {
                buf[24] = '\0';
                mjd = ctime_to_mjd(p);
                sprintf(buf, "--- MJD %12.6lf ---", mjd);
                assert(strlen(buf) == 24);
                // fprintf(stderr, "%d=strlen(%s) != 24\n", strlen(buf), buf);
                memcpy(p, buf, 24);
                count += 1;
                break;
            }
        }

        // Prepend MJD to all lines.
        fprintf(stdout, "%.6lf ", mjd);
        fputs(line, stdout);
    }
    fprintf(stderr, "%ld ctime substitutions\n", count);
}

//
// Look for something like: "Mon Mar 24 11:25:41 2008"
//

int ctime_like (char *s)
{
    // This is a pretty good but not perfect check.
    return strlen(s) >= 24 &&
    isupper(*s++) && islower(*s++) && islower(*s++) &&
    ' ' == *s++ &&
    isupper(*s++) && islower(*s++) && islower(*s++) &&
    ' ' == *s++ &&
    isdigit(*s++) && isdigit(*s++) &&
    ' ' == *s++ &&
    isdigit(*s++) && isdigit(*s++) &&
    ':' == *s++ &&
    isdigit(*s++) && isdigit(*s++) &&
    ':' == *s++ &&
    isdigit(*s++) && isdigit(*s++) &&
    ' ' == *s++ &&
    isdigit(*s++) && isdigit(*s++) && isdigit(*s++) && isdigit(*s++);
}

//
// Convert UTC ctime string to floating point MJD.
//

#define UNIX_TIME_TO_MJD(t) ( MJD_1970_01_01 + ((t) / 86400.0) )
#define MJD_1970_01_01 40587

double ctime_to_mjd (char *s)
{
    static char month[12][3] = {
        "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
    };
    int n;
    time_t t;
    struct tm tm;
    char wday[4], mon[4];

    // Parse ctime string.
    n = sscanf(s, "%3s %3s %d %d:%d:%d %d",
        wday, mon, &tm.tm_mday, &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &tm.tm_year);
    // Set fields.
    if (n == 7) {
        tm.tm_year -= 1900;
        tm.tm_isdst = -1;
        for (tm.tm_mon = 0; tm.tm_mon <= 11; tm.tm_mon += 1) {
            if (strncmp(mon, month[tm.tm_mon], 3) == 0) {
                // Month matches; compute unix time_t and then MJD.
                t = mktime(&tm);
                return UNIX_TIME_TO_MJD(t);
            }
        }
    }
    return 0.0;
}