#include <errno.h>
#include <limits.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include <fuse3/fuse.h>
#include <xcb/xcb.h>
#include <xcb/xcb_util.h>

struct selection
{
	const char * name;
	uint32_t len;
	char * data;
	xcb_atom_t atom;
};

int get_selection_index(const char *);
xcb_window_t find_owner(int);
void update_selection(int);
xcb_atom_t get_atom(xcb_connection_t *, const char *);
int clip_getattr(const char *, struct stat *, struct fuse_file_info *);
int clip_readdir(const char *, void *, fuse_fill_dir_t, off_t, struct fuse_file_info *, enum fuse_readdir_flags);
int clip_open(const char *, struct fuse_file_info *);
int clip_read(const char *, char *, size_t, off_t, struct fuse_file_info *);

const uint32_t mask = XCB_CW_OVERRIDE_REDIRECT | XCB_CW_EVENT_MASK;
const uint32_t values[] = {1, XCB_EVENT_MASK_PROPERTY_CHANGE};
const struct fuse_operations clip_ops = {
	.getattr = clip_getattr,
	.readdir = clip_readdir,
	.open = clip_open,
	.read = clip_read,
};

static xcb_connection_t * c;
static xcb_screen_t * s;
static xcb_window_t w;
static struct selection x[] = {
	{.name = "primary", .len = 0, .data = NULL},
	{.name = "secondary", .len = 0, .data = NULL},
	{.name = "clipboard", .len = 0, .data = NULL},
};


int main(int argc, char ** argv)
{
	c = xcb_connect(NULL, NULL);
	s = xcb_setup_roots_iterator(xcb_get_setup(c)).data;
	w = xcb_generate_id(c);
	xcb_create_window(
		c, XCB_COPY_FROM_PARENT, w, s->root, 0, 0, 1, 1, 0, XCB_COPY_FROM_PARENT, s->root_visual, mask, values);
	xcb_flush(c);
	x[0].atom = get_atom(c, "PRIMARY");
	x[1].atom = get_atom(c, "SECONDARY");
	x[2].atom = get_atom(c, "CLIPBOARD");
	fuse_main(argc, argv, &clip_ops, NULL);
	xcb_disconnect(c);
}


int get_selection_index(const char * path)
{
	for (int i = 0; i < 3; ++i)
		if (0 == strcmp(path + 1, x[i].name))
			return i;
	return -ENOENT;
}


xcb_window_t find_owner(const int i)
{
	xcb_get_selection_owner_cookie_t cookie = xcb_get_selection_owner(c, x[i].atom);
	xcb_get_selection_owner_reply_t * reply = xcb_get_selection_owner_reply(c, cookie, NULL);
	xcb_window_t owner = XCB_WINDOW_NONE;
	if (reply)
		owner = reply->owner;
	free(reply);
	return owner;
}


void update_selection(const int i)
{
	xcb_atom_t TARGET_PROPERTY = get_atom(c, "_TARGET_SELECTION");
	xcb_atom_t UTF8_STRING = get_atom(c, "UTF8_STRING");  // TODO: Look into ways to support various TARGETS.
	if (XCB_WINDOW_NONE == find_owner(i))
		return;
	xcb_convert_selection(c, w, x[i].atom, UTF8_STRING, TARGET_PROPERTY, XCB_CURRENT_TIME);
	xcb_flush(c);
	xcb_generic_event_t * e;
	int done = 0;  // TODO: Look into continuous notifications.
	while (!done)
	{
		e = xcb_wait_for_event(c);
		if (NULL == e) return;
		if (XCB_SELECTION_NOTIFY != XCB_EVENT_RESPONSE_TYPE(e))
		{
			free(e);
			continue;
		}
		xcb_selection_notify_event_t * n = (xcb_selection_notify_event_t *) e;
		if (x[i].atom == n->selection && XCB_NONE != n->property)
		{
			xcb_get_property_cookie_t cookie = xcb_get_property(
				c, 1, w, TARGET_PROPERTY, XCB_ATOM_ANY, 0, UINT32_MAX);
			xcb_get_property_reply_t * reply = xcb_get_property_reply(c, cookie, NULL);
			if (reply)
			{
				const int len = xcb_get_property_value_length(reply);
				x[i].data = realloc(x[i].data, len);
				if (NULL == x[i].data)
					x[i].len = 0;
				x[i].len = len;
				memcpy(x[i].data, xcb_get_property_value(reply), len);
				done = 1;
				free(reply);
			}
		}
		free(e);
	}
}


xcb_atom_t get_atom(xcb_connection_t * c, const char * name)
{
	xcb_intern_atom_cookie_t cookie = xcb_intern_atom(c, 0, strlen(name), name);
	xcb_intern_atom_reply_t * reply = xcb_intern_atom_reply(c, cookie, NULL);
	xcb_atom_t atom = reply->atom;
	free(reply);
	return atom;
}


int clip_getattr(const char * path, struct stat * st, struct fuse_file_info * fi)
{
	(void) fi;
	memset(st, 0, sizeof(struct stat));
	if (0 == strcmp(path, "/"))
	{
		st->st_mode = S_IFDIR | 0755;
		st->st_nlink = 2;
	}
	else
	{
		const int i = get_selection_index(path);
		if (-ENOENT == i)
			return -ENOENT;
		update_selection(i);  // TODO: The content is updated way too often.
		st->st_mode = S_IFREG | 0444;
		st->st_nlink = 1;
		st->st_size = x[i].len;
	}
	return 0;
}


int clip_readdir(
	const char * path, void * buf, fuse_fill_dir_t filler, off_t offset, struct fuse_file_info * fi,
	enum fuse_readdir_flags flags)
{
	(void) offset;
	(void) fi;
	(void) flags;
	if (0 != strcmp(path, "/"))
		return -ENOENT;
	filler(buf, ".", NULL, 0, 0);
	filler(buf, "..", NULL, 0, 0);
	for (int i = 0; i < 3; ++i)
		filler(buf, x[i].name, NULL, 0, 0);
	return 0;
}


int clip_open(const char * path, struct fuse_file_info * fi)
{
	if (-ENOENT == get_selection_index(path))
		return -ENOENT;
	if (O_RDONLY != (fi->flags & O_ACCMODE))
		return -EACCES;
	return 0;  // TODO: Maybe queue selection content retrieval here?
}


int clip_read(const char * path, char * buf, size_t size, off_t offset, struct fuse_file_info * fi)
{
	(void) fi;
	const int i = get_selection_index(path);
	if (-ENOENT == i)
		return -ENOENT;
	update_selection(i);  // TODO: The content is updated way too often.
	if (offset < x[i].len)
	{
		if (offset + size > x[i].len)
			size = x[i].len - offset;
		memcpy(buf, x[i].data + offset, size);
	}
	else
		size = 0;
	return size;
}