//
// utc.exe - Display local time, UTC, and MJD.
//
// - also ${UTC} keyword substitution filter (for web pages)
//
// 22-Feb-2007 tvb
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

void main (int argc, char *argv[])
{
    int mode, sed;
    char *utc (int mode);
    void subst (char *key, char *value);

    sed = 0;
    if (argc > 1 && strcmp(argv[1], "/s") == 0) {
        argc -= 1;
        argv += 1;
        sed = 1;
    }

    mode = (argc > 1) ? atoi(argv[1]) : 7;

    if (sed) {
        subst("${UTC}", utc(mode));

    } else {
        printf("%s\n", utc(mode));
    }
}

//
// Generate UTC or MJD string.
//

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

char *utc (int mode)
{
    double mjd;
    time_t now;
    struct tm *tm;
    char *zonename (char *name);
    char *p;
    static char utc[100]; // STATIC

    time(&now);
    mjd = UNIX_TIME_TO_MJD(now);

    // Display local time.

    tm = localtime(&now);
    p = utc;
    if (mode & 1) {
        p += sprintf(p, "%.24s %s", ctime(&now), zonename(_tzname[tm->tm_isdst]));
    }

    // One way to display UTC is jam timezone to zero.

    _timezone = 0;
    _daylight = 0;
    if (mode & 2) {
        if (p != utc) {
            p += sprintf(p, " = ");
        }
        p += sprintf(p, "%.24s %s", ctime(&now), "UTC");
    }

    // Display MJD (Modified Julian Date).

    if (mode & 4) {
        if (p != utc) {
            p += sprintf(p, " = ");
        }
        p += sprintf(p, "MJD %.6lf", mjd);
    }

    return utc; // STATIC
}

//
// Extract short abbreviation from full time zone name.
//

char *zonename (char *name)
{
    int i;
    char *p;
    static char zone[4];

    i = 0;
    for (p = name; *p && i < 3; p += 1) {
        if (*p >= 'A' && *p <= 'Z') {
            zone[i] = *p;
            i += 1;
        }
    }
    zone[i] = '\0';

    return zone;
}

//
// A sed-like stdin-stdout filter for keyword substitution.
//

void subst (char *key, char *value)
{
    int i, k, n;
    char line[1000], *p;

    k = strlen(key);
    while (fgets(line, sizeof(line), stdin) != NULL) {
        p = strstr(line, key);
        if (p != NULL) {
            i = p - line;
            n = strlen(line);

            fwrite(line, i, 1, stdout);
            fwrite(value, strlen(value), 1, stdout);
            fwrite(line + i + k, n - i - k, 1, stdout);

        } else {
            fputs(line, stdout);
        }
    }
}