/*
##% gcc -Wall -g -o $STEM $FILE
*/

#include <sys/file.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>

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

static void
quit(int sig)
{
  exit(0);
}

#include <sys/time.h>
/*
char *
timestamp() {
  struct timeval tv;
  gettimeofday(&tv, NULL);
  static char buf[10];

  int64_t ms = tv.tv_sec * 1000 + tv.tv_usec / 1000;

  buf[9] = 0;
  int i;
  for (i = 8; i >= 0; i--) {
    buf[i] = 'a' + (ms % 26);
    ms /= 26;
  }
  
  return buf;
}
*/

int
main(int argc, char *argv[])
{
  pid_t child;
  int lockfd;
  char lockfile[128];
  int dirfd;

  struct timeval tv;
  gettimeofday(&tv, NULL);
  int64_t ms = tv.tv_sec * 1000 + tv.tv_usec / 1000;

  char *path = getenv("NQDIR");
  if (!path)
    path = ".";

  dirfd = open(path, O_RDONLY);
  if (dirfd < 0) {
    perror("dir open");
    exit(111);
  }

  child = fork();
  if (child == -1) {
    perror("fork");
    exit(111);
  }

  if (child > 0) {
    // background
    signal(SIGINT, quit);
    pause();
    exit(0);
  }

  child = fork();
  if (child == -1) {
    perror("fork");
    exit(111);
  }
  if (child > 0) {
    int status;
    sprintf(lockfile, ",%lx.%d", ms, child);

    puts(lockfile);

    // signal parent to exit
    kill(getppid(), SIGINT);

    wait(&status);
    int fd;
    fd = openat(dirfd, lockfile, O_RDWR | O_APPEND);
    fchmod(fd, 0600);
    if (WIFEXITED(status))
      dprintf(fd, "\n[exited with status %d.]\n", WEXITSTATUS(status));
    else
      dprintf(fd, "\n[killed by signal %d.]\n", WTERMSIG(status));

    exit(0);
  }

  sprintf(lockfile, ".,%lx.%d", ms, getpid());
  lockfd = openat(dirfd, lockfile, O_CREAT | O_EXCL | O_RDWR | O_APPEND, 0600);
  
  if (lockfd < 0) {
    perror("open");
    exit(222);
  }

  flock(lockfd, LOCK_EX);
  
  // drop leading .
  renameat(dirfd, lockfile, dirfd, lockfile+1);

  write(lockfd, "exec", 4);
  int i;
  for (i = 0; i < argc; i++) {
      int j, l = strlen(argv[i]);
      write(lockfd, " '", 2);
      for (j = 0; j < l; j++) {
        if (argv[i][j] == '\'')
          write(lockfd, "'\\''", 4);
        else
          write(lockfd, argv[i]+j, 1);
      }
      write(lockfd, "'", 1);
  }

  DIR *dir = fdopendir(dirfd);
  if (!dir) {
    perror("fdopendir");
    exit(111);
  }

  struct dirent *ent;

again:
  while ((ent = readdir(dir))) {
    if (ent->d_name[0] == ',' && strcmp(ent->d_name, lockfile+1) < 0) {
      int f = openat(dirfd, ent->d_name, O_RDWR);
    
      if (flock(f, LOCK_EX | LOCK_NB) == -1 && errno == EWOULDBLOCK) {
        flock(f, LOCK_EX);   // sit it out

        rewinddir(dir);
        goto again;
      }
    
      fchmod(f, 0600);
      close(f);
    }
  }

  closedir(dir);

  // ready to run

  write(lockfd, "\n", 1);

  fchmod(lockfd, 0700);
  
  dup2(lockfd, 2);
  dup2(lockfd, 1);
  close(lockfd);
  close(dirfd);

  execvp(argv[1], argv+1);

  return 111;
}