#define _GNU_SOURCE     /* Needed to get O_LARGEFILE definition */
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/fanotify.h>
#include <unistd.h>
#include <string.h>
#include <time.h>

//json-writer.c prototypes
void json_write_filename_bytes(const char *input, size_t length, FILE *out);

size_t get_parent_dir(char* path, int mount_fd, struct file_handle* fh) {
	int parent_fd = open_by_handle_at(mount_fd, fh, O_PATH | O_DIRECTORY);

	if (parent_fd == -1) {
		if (errno == ESTALE) {
			fprintf(stderr, "File handle is no longer valid. File has been deleted\n");
			return 0;
		} else {
			perror("open_by_handle_at");
			exit(EXIT_FAILURE);
		}
	}

	char procfd_path[PATH_MAX];
	snprintf(procfd_path, sizeof(procfd_path), "/proc/self/fd/%d", parent_fd);

	size_t path_len = readlink(procfd_path, path, PATH_MAX);
	close(parent_fd);
	return path_len;
}



static void handle_events(int fafd, int mount_fd) {
	struct fanotify_event_metadata buf[200];
	while (true) {
		ssize_t size = read(fafd, buf, sizeof(buf));
		if (size == -1 && errno != EAGAIN) {
			perror("read");
			exit(EXIT_FAILURE);
		}

		if (size > 0) {
			const struct fanotify_event_metadata* metadata = buf;

			while (FAN_EVENT_OK(metadata, size)) {
				if (metadata->vers != FANOTIFY_METADATA_VERSION) {
					fprintf(stderr, "Mismatch of fanotify metadata version.\n");
					exit(EXIT_FAILURE);
				}

				struct timespec mono, wall;
				clock_gettime(CLOCK_MONOTONIC, &mono);
				clock_gettime(CLOCK_REALTIME, &wall);

				fprintf(stdout, "{\"ts\": [%li, %li, %li, %li]", wall.tv_sec, wall.tv_nsec, mono.tv_sec, mono.tv_nsec);

				char *ptr = (char *)(metadata + 1);
				char *end = (char *)metadata + metadata->event_len;
				int entry_index = 0;
				while (ptr < end) {
					struct fanotify_event_info_header *hdr = (struct fanotify_event_info_header *)ptr;

					if (hdr->info_type == FAN_EVENT_INFO_TYPE_DFID_NAME ||
						hdr->info_type == FAN_EVENT_INFO_TYPE_OLD_DFID_NAME ||
						hdr->info_type == FAN_EVENT_INFO_TYPE_NEW_DFID_NAME) {

						struct fanotify_event_info_fid *fid = (struct fanotify_event_info_fid *)hdr;
						struct file_handle *fh = (struct file_handle *)fid->handle;
						char parent_path[PATH_MAX];
						size_t parent_path_length = get_parent_dir(parent_path, mount_fd, fh);
						char *name = (char *)fh->f_handle + fh->handle_bytes;

						if (hdr->info_type == FAN_EVENT_INFO_TYPE_OLD_DFID_NAME) {
							fprintf(stdout, ", \"old\": ");
						} else if (hdr->info_type == FAN_EVENT_INFO_TYPE_NEW_DFID_NAME) {
							fprintf(stdout, ", \"new\": ");
						} else {
							fprintf(stdout, ", \"name\": ");
						}

						fputc('"', stdout);
						json_write_filename_bytes(parent_path, parent_path_length, stdout);
						fputc('/', stdout);
						json_write_filename_bytes(name, strlen(name), stdout);
						fputc('"', stdout);

					}



					ptr += hdr->len;
				}

				if (entry_index++) { fprintf(stdout, ", "); }
				fprintf(stdout, ", \"mask\": %lli}\n", metadata->mask);

				metadata = FAN_EVENT_NEXT(metadata, size);

			}
		} else {
			break;
		}

	}

}

int main(int argc, char *argv[]) {

	// Acquire arguments
	if (argc != 2) {
		fprintf(stderr, "Usage: %s MOUNT\n", argv[0]);
		exit(EXIT_FAILURE);
	}
	char* mount_point = argv[1];

	// Open mount point for reading
	int mount_fd = open(mount_point, O_DIRECTORY | O_RDONLY);
	if (mount_fd == -1) {
		perror(mount_point);
		exit(EXIT_FAILURE);
	}

	// Create file descriptor for fanotify API
	int fafd = fanotify_init(FAN_CLOEXEC | FAN_CLASS_NOTIF | FAN_NONBLOCK | FAN_REPORT_FID | FAN_REPORT_DFID_NAME, O_RDONLY | O_LARGEFILE);
	if (fafd == -1) {
		perror("fanotify_init");
		exit(EXIT_FAILURE);
	}

	// Mark events for logging
	if (fanotify_mark(fafd, FAN_MARK_ADD | FAN_MARK_FILESYSTEM, FAN_ATTRIB | FAN_RENAME | FAN_CREATE | FAN_DELETE | FAN_CLOSE_WRITE | FAN_ONDIR, AT_FDCWD, mount_point) == -1) {
		perror("fanotify_mark");
		exit(EXIT_FAILURE);
	}

	// Setup file descriptors for epoll
	#define N_POLL_FDS 1
	struct pollfd poll_fds[N_POLL_FDS] = {
		{.fd = fafd, .events = POLLIN},
	};

	fprintf(stderr, "Listening for events.\n");
	fprintf(stderr, "Issue interrupt signal to terminate.\n");

	while (1) {
		int poll_num = poll(poll_fds, N_POLL_FDS, -1);
		if (poll_num == -1) {
			if (errno == EINTR)	// Interrupted by signal
				continue;
			perror("poll");     // Unexpected error
			exit(EXIT_FAILURE);
		}
		if (poll_num >= 0) {
			if (poll_fds[0].revents & POLLIN) {	// fanotify events available
				handle_events(fafd, mount_fd);
				fflush(stdout);
			}
		}
	}
	fprintf(stderr, "Listening for events stopped.\n");
	exit(EXIT_SUCCESS);
}