/*
 * enigma/misc.c - provide miscellaneous utility routines.
 *
 * Copyright 2000 Simon Tatham. All rights reserved.
 *
 * Enigma is licensed under the MIT licence. See the file LICENCE for
 * details.
 *
 * - we are all amf -
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#ifndef _WIN32
#  include <unistd.h>
#  include <pwd.h>
#endif
#include <sys/types.h>

#include "enigma.h"

char *fatal_error_string;
jmp_buf fatal_error_jmp_buf;

void fatal(const char *string) {
    fatal_error_string = malloc(1+strlen(string));
    if (fatal_error_string)
	strcpy(fatal_error_string, string);
    longjmp(fatal_error_jmp_buf, 1);
}

/*
 * See if a line begins with a given header text.
 */
int ishdr(char *line, const char *header) {
    return !strncmp(line, header, strlen(header));
}

/*
 * Determine a username to use for saving and loading progress and
 * game positions.
 */
void get_user(char *buf, int buflen) {
#ifdef _WIN32
    if (!GetUserName(buf, &buflen))
	strncpy(buf, "unknown", buflen);
#else
    struct passwd *p;
    uid_t uid = getuid();
    char *user;

    /*
     * First, find who we think we are using getlogin. If this
     * agrees with our uid, we'll go along with it. This should
     * allow sharing of uids between several login names whilst
     * coping correctly with people who have su'ed.
     */
    user = getlogin();
    setpwent();
    if (user)
	p = getpwnam(user);
    else
	p = NULL;
    if (p && p->pw_uid == uid) {
	/*
	 * The result of getlogin() really does correspond to our
	 * uid. Fine.
	 */
	strncpy(buf, user, buflen);
	buf[buflen-1] = '\0';
    } else {
	/*
	 * If that didn't work, for whatever reason, we'll do the
	 * simpler version: look up our uid in the password file
	 * and map it straight to a name.
	 */
	p = getpwuid(uid);
	strncpy(buf, p->pw_name, buflen);
	buf[buflen-1] = '\0';
    }
    endpwent();
#endif
}

/*
 * Routines to get around the fact that C's time handling is awful.
 * With no direct inverse to gmtime(), and no standards-compliant
 * way to read and write a time_t directly, what standard format
 * can there possibly be for times that ports across time zones?
 *
 * Well, it can just about be done. Here's how.
 */

/* ----------------------------------------------------------------------
 * This completely ANSI-compliant function determines the timezone shift
 * in seconds. (E.g. if local time were 1 hour ahead of GMT, this routine
 * would return 3600.) This timezone shift is to normal local time, not to
 * DST local time.
 */
static long tzshift(void) {
    time_t t1, t2;
    struct tm tm;
    t1 = time(NULL);
    tm = *gmtime(&t1);
    tm.tm_isdst = 0;		       /* should already be; let's make sure */
    t2 = mktime(&tm);
    /*
     * So tm is t1 formatted as GMT, and is also t2 formatted as
     * local time. Hence difftime(t1,t2) gives the number of
     * seconds by which local time is ahead of GMT. We'll assume
     * here that the number of seconds will fit in a long, since
     * for it not to do so would have to imply a time zone 68
     * _years_ different from GMT.
     */
    return (long)difftime(t1,t2);
}

/* ----------------------------------------------------------------------
 * This completely ANSI-compliant function adjusts a `struct tm' by
 * a given number of seconds.
 */
static void adjust_tm(struct tm *tm, long seconds) {
    int sign = seconds < 0 ? -1 : +1;
    seconds = labs(seconds);
    mktime(tm);			       /* normalise the tm structure */
    tm->tm_mday += sign * (seconds / 86400);
    tm->tm_hour += sign * (seconds / 3600) % 24;
    tm->tm_sec += sign * (seconds % 3600);
    mktime(tm);			       /* normalise the tm structure again */
}

/* ----------------------------------------------------------------------
 * With the aid of the above two functions, _this_ completely ANSI-
 * compliant function is the equivalent of mktime() using GMT. In
 * other words, it's the inverse of gmtime().
 */
static time_t mktimegm(struct tm *tm) {
    tm->tm_isdst = 0;		       /* GMT is never daylight-saving */
    /*
     * If local time is an hour ahead of GMT, then calling mktime
     * on tm will give us a result one hour _earlier_ than what we
     * want, so we would have to add an hour to tm before calling
     * mktime.
     */
    adjust_tm(tm, tzshift());
    return mktime(tm);
}

/*
 * Progress files store dates in GMT, in the format YYYY/MM/DD hh:mm:ss.
 */

/*
 * Parse a date in progress-file format.
 */
time_t parse_date(char *buf) {
    struct tm tm;
    int year, month;

    sscanf(buf, "%d/%d/%d %d:%d:%d", &year, &month, &tm.tm_mday,
	   &tm.tm_hour, &tm.tm_min, &tm.tm_sec);
    tm.tm_year = year - 1900;
    tm.tm_mon = month - 1;
    return mktimegm(&tm);
}

/*
 * Format a date in progress-file format.
 */
void fmt_date(char *buf, time_t t) {
    struct tm tm;

    tm = *gmtime(&t);

    sprintf(buf, "%04d/%02d/%02d %02d:%02d:%02d",
	    1900+tm.tm_year, 1+tm.tm_mon, tm.tm_mday,
	    tm.tm_hour, tm.tm_min, tm.tm_sec);
}