// SPDX-License-Identifier: GPL-2.0
/*
 * fusectl test file-system
 * Creates a simple FUSE filesystem with a single read-write file (/test)
 */

#define FUSE_USE_VERSION 26

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

#define MAX(a, b) ((a) > (b) ? (a) : (b))

static char *content;
static size_t content_size = 0;
static const char test_path[] = "/test";

static int test_getattr(const char *path, struct stat *st)
{
        memset(st, 0, sizeof(*st));

        if (!strcmp(path, "/")) {
                st->st_mode = S_IFDIR | 0755;
                st->st_nlink = 2;
                return 0;
        }

        if (!strcmp(path, test_path)) {
                st->st_mode = S_IFREG | 0664;
                st->st_nlink = 1;
                st->st_size = content_size;
                return 0;
        }

        return -ENOENT;
}

static int test_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
                        off_t offset, struct fuse_file_info *fi)
{
        if (strcmp(path, "/"))
                return -ENOENT;

        filler(buf, ".", NULL, 0);
        filler(buf, "..", NULL, 0);
        filler(buf, test_path + 1, NULL, 0);

        return 0;
}

static int test_open(const char *path, struct fuse_file_info *fi)
{
        if (strcmp(path, test_path))
                return -ENOENT;

        return 0;
}

static int test_read(const char *path, char *buf, size_t size, off_t offset,
                     struct fuse_file_info *fi)
{
        if (strcmp(path, test_path) != 0)
                return -ENOENT;

        if (!content || content_size == 0)
                return 0;

        if (offset >= content_size)
                return 0;

        if (offset + size > content_size)
                size = content_size - offset;

        memcpy(buf, content + offset, size);

        return size;
}

static int test_write(const char *path, const char *buf, size_t size,
                      off_t offset, struct fuse_file_info *fi)
{
        size_t new_size;

        if (strcmp(path, test_path) != 0)
                return -ENOENT;

        if(offset > content_size)
                return -EINVAL;

        new_size = MAX(offset + size, content_size);

        if (new_size > content_size)
                content = realloc(content, new_size);

        content_size = new_size;

        if (!content)
                return -ENOMEM;

        memcpy(content + offset, buf, size);

        return size;
}

static int test_truncate(const char *path, off_t size)
{
        if (strcmp(path, test_path) != 0)
                return -ENOENT;

        if (size == 0) {
                free(content);
                content = NULL;
                content_size = 0;
                return 0;
        }

        content = realloc(content, size);

        if (!content)
                return -ENOMEM;

        if (size > content_size)
                memset(content + content_size, 0, size - content_size);

        content_size = size;
        return 0;
}

static struct fuse_operations memfd_ops = {
        .getattr = test_getattr,
        .readdir = test_readdir,
        .open = test_open,
        .read = test_read,
        .write = test_write,
        .truncate = test_truncate,
};

int main(int argc, char *argv[])
{
        return fuse_main(argc, argv, &memfd_ops, NULL);
}