#include "tag.h"

int
move(int fd, long to, long from)
{
	char buf[16*1024];
	int n;

	if(to > from)
		abort();

	while((n = pread(fd, buf, sizeof buf, from)) > 0) {
		if(pwrite(fd, buf, n, to) < n) {
			werrstr("write: %r");
			return -1;
		}
		to += n;
		from += n;
	}
	if(n < 0) {
		werrstr("read: %r");
		return -1;
	}

	return 0;
}

void
usage(void)
{
	fprint(2, "usage: %s file\n", argv0);
	exits("usage");
}

void
main(int argc, char **argv)
{
	uchar buf[HeaderSize], *p;
	int fd;
	Header hdr;
	Dir *dir;
	vlong newlength;

	ARGBEGIN {
	default:
		usage();
	} ARGEND

	if(argc != 1)
		usage();

	if((fd = open(argv[0], ORDWR)) < 0)
		sysfatal("open %s: %r", argv[0]);

	if(readn(fd, buf, HeaderSize) < 0)
		sysfatal("couldn't read header: %r");

	p = buf;
	gheader(&p, &hdr);
	if(strcmp(hdr.magic, "ID3") == 0) {
		if((dir = dirfstat(fd)) == nil)
			sysfatal("stat %s: %r", argv[0]);
		if(move(fd, 0, HeaderSize + hdr.length) < 0)
			sysfatal("move: %r");
		newlength = dir->length - (HeaderSize + hdr.length);
		nulldir(dir);
		dir->length = newlength;
		if(dirfwstat(fd, dir) < 0)
			sysfatal("wstat %s: %r", argv[0]);
	}

	exits(nil);
}

// FIXME -- only tags at the beginning of the file will be removed