#include <sys/time.h>
#include <dlfcn.h>
#include <sys/timeb.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>


typedef int (*gettimeofday_func_t)(struct timeval *tv, struct timezone *tz);
static gettimeofday_func_t gettimeofday_orig;

typedef time_t (*time_func_t)(time_t *t);
static time_func_t time_orig;

typedef int (*ftime_func_t)(struct timeb *tp);
static ftime_func_t ftime_orig;

static time_t wayback=0;


static int inside=0;
static pthread_mutex_t inside_mutex=PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;

static void enter(void)
{
static int done=0;
void *libc_handle;
char *wayback_s;

	if (pthread_mutex_lock(&inside_mutex)) {
		fprintf(stderr,"libwayback: 'inside_mutex' lock fail!\n");
		_exit(1);
		}
	if (inside<0) {
		fprintf(stderr,"libwayback: 'inside' sanity fail!\n");
		_exit(1);
		}
	if (inside) {
		fprintf(stderr,"libwayback: looping!\n");
		_exit(1);
		}
	inside++;

	if (done)
		return;
	done=1;

	if ((wayback_s=getenv("WAYBACK")))
		wayback=atol(wayback_s);

	libc_handle=dlopen("/lib/libc.so.6",RTLD_LAZY);	/* RTLD_LAZY is mandatory */
	gettimeofday_orig=(gettimeofday_func_t)dlsym(libc_handle,"gettimeofday");
	time_orig=(time_func_t)dlsym(libc_handle,"time");
	ftime_orig=(ftime_func_t)dlsym(libc_handle,"ftime");
}

static void leave(void)
{
	if (inside!=1) {
		fprintf(stderr,"libwayback: 'inside' sanity fail!\n");
		_exit(1);
		}
	inside--;
	if (pthread_mutex_unlock(&inside_mutex)) {
		fprintf(stderr,"libwayback: 'inside_mutex' unlock fail!\n");
		_exit(1);
		}
}


int gettimeofday(struct timeval *tv, struct timezone *tz)
{
int r;

	enter();

	r=(*gettimeofday_orig)(tv,tz);
	if (tv)
		tv->tv_sec-=wayback;

	leave();

	return r;
}


time_t time(time_t *t)
{
time_t r;

	enter();
	r=(*time_orig)(t);

	if (t)
		*t-=wayback;
	r-=wayback;

	leave();
	return r;
}


int ftime(struct timeb *tp)
{
int r;

	enter();
	r=(*ftime_orig)(tp);
	
	if (tp)
		tp->time-=wayback;

	leave();
	return r;
}