#include <string.h>
#include <stdio.h>

#include "mount.h"
#include "path.h"
#include "bug.h"

char *cut_root_for_bind(char *target_root, char *source_root)
{
	int tok = 0;
	char *path = NULL;
	/*
	 * Cut common part of root.
	 * For non-root binds the source is always "/" (checked)
	 * so this will result in this slash removal only.
	 */
	while (target_root[tok] == source_root[tok]) {
		tok++;
		if (source_root[tok] == '\0') {
			path = target_root + tok;
			goto out;
		}
		if (target_root[tok] == '\0') {
			path = source_root + tok;
			goto out;
		}
	}

	return NULL;
out:
	BUG_ON(path == NULL);
	if (path[0] == '/')
		path++;

	return path;
}

char *mnt_get_sibling_path(struct mount_info *m,
			   struct mount_info *p, char *buf, int len)
{
	struct mount_info *pa = m->parent;
	char *rpath, *cut_root, *path = buf;
	int off = 0;

	if (pa == NULL)
		return NULL;

	rpath = m->mountpoint + strlen(pa->mountpoint);
	if (rpath[0] == '/')
		rpath++;

	/*
	 * Get a path to a sibling of "m" with parent "p",
	 * return NULL is p can't have a sibling of m.
	 *
	 * Here are two cases:
	 * When a parent of "m" has longer root than "p":
	 * /    pm->root            / rpath
	 *               | cut_root |
	 * /    p->root  /
	 * In this case, a sibling path is a sum of p->mountpoint,
	 * cut_root and rpath.
	 *
	 * When a parent of m has shorter root than "p":
	 * /    pm->root /            rpath
	 *               | cut_root |
	 * /    p->root             / rpath +strlen(cut_root)
	 * In this case, a sibling path is a sum of p->mountpoint and
	 * rpath - strlen(cut_root).
	 */

	cut_root = cut_root_for_bind(pa->root, p->root);
	if (cut_root == NULL)
		return NULL;
	if (p->mountpoint[1] != 0) /* not "/" */
		off = snprintf(path, len, "%s", p->mountpoint);
	if (path[off - 1] == '/') /* p->mountpoint = "./" */
		off--;
	len -= off;
	path += off;

	if (strlen(pa->root) > strlen(p->root)) {
		off = snprintf(path, len, "/%s", cut_root);
		len -= off;
		path += off;
	} else {
		int len = strlen(cut_root);
		if (strncmp(rpath, cut_root, len))
			return NULL;
		rpath += strlen(cut_root);
		if (len > 0 && (rpath[0] && rpath[0] != '/'))
			return NULL;
	}
	if (rpath[0] == '/')
		rpath++;

	off = snprintf(path, len, "/%s", rpath);

	return buf;
}
