#include <sys/inotify.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <fcntl.h>
#include <dirent.h>

#define BUFFER_LEN (1024 * (sizeof(struct inotify_event) + 16))

void handle_cgroup_event(const char *event_file) {
  char buffer[256];
  int fd = open(event_file, O_RDONLY);
  if(fd < 0) {
    return;
  }

  ssize_t bytesRead = read(fd, buffer, sizeof(buffer) - 1);
  close(fd);
  if(bytesRead < 0) {
    return;
  }

  buffer[bytesRead] = '\0';

  if(strstr(buffer, "populated 0")) {
    char dir[1024];
    strcpy(dir, event_file);
    *strrchr(dir, '/') = '\0';
    rmdir(dir);
  }
}

void scan_and_clean_cgroup_directory(const char *dir) {
  DIR *d = opendir(dir);
  if (!d) {
    return;
  }

  struct dirent *entry;
  while ((entry = readdir(d)) != NULL) {
    if (entry->d_type == DT_DIR) {
      if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0) {
        continue;
      }

      char subdir[1024];
      snprintf(subdir, sizeof(subdir), "%s/%s/cgroup.events", dir, entry->d_name);
      handle_cgroup_event(subdir);
    }
  }

  closedir(d);
}

void monitor_directory(const char *dir) {
  int inotify_fd = inotify_init();
  if(inotify_fd < 0) {
    exit(EXIT_FAILURE);
  }

  int wd = inotify_add_watch(inotify_fd, dir, IN_CREATE);
  if(wd < 0) {
    close(inotify_fd);
    exit(EXIT_FAILURE);
  }

  char buffer[BUFFER_LEN];
  while(1) {
    ssize_t length = read(inotify_fd, buffer, BUFFER_LEN);
    if(length < 0) {
      close(inotify_fd);
      exit(EXIT_FAILURE);
    }

    char *ptr;
    for(ptr = buffer; ptr < buffer + length; ptr += sizeof(struct inotify_event) + ((struct inotify_event *)ptr)->len) {
      struct inotify_event *event = (struct inotify_event *)ptr;
      if(event->mask & IN_CREATE && event->mask & IN_ISDIR) {
        char cgroup_event_path[1024];
        snprintf(cgroup_event_path, sizeof(cgroup_event_path), "%s/%s/cgroup.events", dir, event->name);

        sleep(1);

        int cgroup_event_wd = inotify_add_watch(inotify_fd, cgroup_event_path, IN_MODIFY);
        if(cgroup_event_wd >= 0) {
          handle_cgroup_event(cgroup_event_path);
        }
      } else if(event->mask & IN_MODIFY) {
        char cgroup_event_path[1024];
        snprintf(cgroup_event_path, sizeof(cgroup_event_path), "%s/%s/cgroup.events", dir, event->name);
        handle_cgroup_event(cgroup_event_path);
      }
    }
  }

  close(inotify_fd);
}

int main(int argc, char *argv[]) {
  const char *cgroup_dir = "/sys/fs/cgroup";
  int run_as_daemon = (argc > 1 && strcmp(argv[1], "--daemon") == 0);

  scan_and_clean_cgroup_directory(cgroup_dir);

  if(run_as_daemon) {
    if(fork() > 0) exit(EXIT_SUCCESS);
    if(setsid() < 0) exit(EXIT_FAILURE);
    if(fork() > 0) exit(EXIT_SUCCESS);

    chdir("/");
    for(int x = sysconf(_SC_OPEN_MAX); x >= 0; x--) {
      close(x);
    }

    open("/dev/null", O_RDWR);
    dup(0);
    dup(0);

    monitor_directory(cgroup_dir);
  }

  return 0;
}