#include <stdio.h>
#include <unistd.h>
#include <sysexits.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/vt.h>

struct vt_scrollparms sp;

int openconsole(void) {
	char *dev = "/dev/console";
	int fd;

	fd = open(dev, O_RDWR);
	if(fd == -1) {
		perror("unable to open console");
		return(-1);
	}
	return(fd);
}

int enable_scrollback(void) {
	int ret, fd;
	fd = openconsole();

	if(fd == -1)
		return(EX_TEMPFAIL);

	ret = ioctl(fd, VT_ENABLESCROLLBACK);
	if(ret == -1) {
		perror("unable to enable scrollback");
		return(EX_TEMPFAIL);
	}
	return(EX_OK);
}

int set_scrollback(void) {
	int ret, fd;

	fd = openconsole();

	if(fd == -1)
		return(EX_TEMPFAIL);

	ret = ioctl(fd, VT_SETSCROLLBACK, &sp);
	if(ret == -1) {
		perror("unable to configure scrollback");
		return(EX_TEMPFAIL);
	}
	return(EX_OK);
}

int get_scrollback(void) {
	int ret, fd;

	fd = openconsole();

	if(fd == -1)
		return(EX_TEMPFAIL);
	
	ret = ioctl(fd, VT_GETSCROLLBACK, &sp);
	if(ret == -1) {
		perror("unable to get scrollback parameters");
		return(EX_TEMPFAIL);
	}
	return(EX_OK);
}

int clear_scrollback(void) {
	unsigned int savesize;
	int ret;

	ret = get_scrollback();
	if(ret != EX_OK) 
		return(ret);

	savesize = sp.vp_size;
	sp.vp_size = 0;

	ret = set_scrollback();
	if(ret != EX_OK)
		return(ret);

	sp.vp_size = savesize;

	return(set_scrollback());
}
	
int main(int argc, char **argv) {
	/* usage: cfgscroll -e
	   enable global scrollback (cannot be disabled)
	   usage: cfgscroll -s con size
	   set scrollback for specific console
	   usage: cfgscroll -g con
	   get scrollback for specific console
	   usage: cfgscroll -c con
	   clear scrollback for specific console */
	int ret;

	if(argc == 2) {
		if(!strcmp(argv[1], "-e")) 
			return(enable_scrollback());
		goto dispusage;
	} else if(argc == 3) {
		if(!strcmp(argv[1], "-g")) {
			sscanf(argv[2], "%u", &sp.vp_con);
			ret = get_scrollback();
			if(ret == EX_OK);
				printf("console %u: max scrollback = %u\n", sp.vp_con, sp.vp_size);
			return(ret);
		} else if(!strcmp(argv[1], "-c")) {
			sscanf(argv[2], "%u", &sp.vp_con);
			return(clear_scrollback());
		}
		goto dispusage;
	} else if(argc == 4) {
		if(!strcmp(argv[1], "-s")) {
			sscanf(argv[2], "%u", &sp.vp_con);
			sscanf(argv[3], "%u", &sp.vp_size);
			return(set_scrollback());
		}
	}

dispusage:
	printf("usage: cfgscroll [-e] || [-s console size] || [-g console] || [-c console]\n");
	exit(EX_USAGE);
}