/* recdate.c   by Michael Thorpe   2012-12-12 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>

#define USAGE "usage: recdate [-m] [<format>]\n"

#define MAX_FORMAT 32 /* Maximum chars to be printed in a custom format */

static int doit(int onlyminutes,char *format) {
	time_t old=0,new;
	struct timeval tv;
	struct tm *tm;
	char *s=0,*t; /* The s=0 is just to shut gcc up. */
	size_t l;

	if(format) {
		s=(char *)malloc(MAX_FORMAT+1);
		if(!s) {
			perror("malloc");
			return(-1);
		}
	}
	if(gettimeofday(&tv,0))
		return(-1);
	while(1) {
		new=tv.tv_sec;
		if(old != new) {
			if(format) {
				tm=localtime(&new);
				l=strftime(s,MAX_FORMAT,format,tm)+1;
			} else {
				t=ctime(&new);
				l=strlen(t);
				if(t[l-1] != '\n') {
					fputs("Last character of ctime wasn't '\\n'!\n",stderr);
					return(-1);
				}
#if ITS_NOT_OK_TO_MODIFY_CTIMES_BUFFER
				s=(char *)malloc(l+1);
				memcpy(s,t,l-1);
#else
				s=t;
#endif
			}
			s[l-1]='\r';
			if(l != fwrite(s,1,l,stdout) || fflush(stdout)) {
				perror("write");
				return(-1);
			}
#if ITS_NOT_OK_TO_MODIFY_CTIMES_BUFFER
			free(s);
#endif
			old=new;
		}
		if(gettimeofday(&tv,0))
			return(-1);
		if(onlyminutes)
			tv.tv_sec=59-(tv.tv_sec%60);
		else
			tv.tv_sec=0;
		if(0==tv.tv_usec)
			tv.tv_sec++;
		else
			tv.tv_usec=1000000-tv.tv_usec;
		if(select(0,0,0,0,&tv))
			return(-1);
		if(gettimeofday(&tv,0))
			return(-1);
		if(500000<tv.tv_usec) {
/* FreeBSD tends to undersleep on long sleeps, so only warn if sec==0 */
			if(!(onlyminutes && 59==(tv.tv_sec%60)))
				fprintf(stderr,"\nwarning: slept until .%06lus into the new second\n",tv.tv_usec);
		}
	}
	return(0);
}

int main(int argc,char **argv) {
	int onlyminutes=0;

	if(argc>1 && argv[1][0]=='-' && argv[1][1]=='m' && !argv[1][2]) {
		onlyminutes=1;
		argc--;
		argv++;
	}
	if(argc>1 && argv[1][0]=='-' && argv[1][1]=='h' && !argv[1][2]) {
		fputs(USAGE,stdout);
		return(0);
	}
	if(argc==2)
		return(doit(onlyminutes,argv[1]));
	if(argc != 1) {
		fputs(USAGE,stderr);
		return(1);
	}
	return(doit(onlyminutes,0));
}