#define _GNU_SOURCE
#include <dirent.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/stat.h>
#include <unistd.h>

#define MAX_PATH_LEN 4096

static void usage (void) __attribute__ ((unused));

// WARNING WARNING WARNING:
// When using opendir and readdir to read directory listings, the files
// are returned in the order they were created. There is randomness to that
// creation that can cause tests to fail. You MUST sort the file names as
// expected in the test case files. To avoid making your task harder than
// it needs to be, we strongly suggest you use scandir instead.

int
filename_cmp (const struct dirent **a, const struct dirent **b)
{
  const char *name1 = (*a)->d_name;
  const char *name2 = (*b)->d_name;

  while (*name1 == '.')
    name1++;
  while (*name2 == '.')
    name2++;

  return strcasecmp (name1, name2);
}

void
print_permissions (mode_t mode)
{
  char perms[11];

  perms[0] = S_ISDIR (mode) ? 'd' : '-';
  perms[1] = (mode & S_IRUSR) ? 'r' : '-';
  perms[2] = (mode & S_IWUSR) ? 'w' : '-';
  perms[3] = (mode & S_IXUSR) ? 'x' : '-';
  perms[4] = (mode & S_IRGRP) ? 'r' : '-';
  perms[5] = (mode & S_IWGRP) ? 'w' : '-';
  perms[6] = (mode & S_IXGRP) ? 'x' : '-';
  perms[7] = (mode & S_IROTH) ? 'r' : '-';
  perms[8] = (mode & S_IWOTH) ? 'w' : '-';
  perms[9] = (mode & S_IXOTH) ? 'x' : '-';
  perms[10] = '\0';

  printf ("%s", perms);
}

int
main (int argc, char *argv[])
{
  int opt;
  int a_flag = false, p_flag = false, s_flag = false;

  while ((opt = getopt (argc, argv, "aps")) != -1)
    {
      switch (opt)
        {
        case 'a':
          a_flag = true;
          break;
        case 'p':
          p_flag = true;
          break;
        case 's':
          s_flag = true;
          break;
        default:
          printf ("./bin/ls: invalid option -- \'%c\'\n", optopt);
          exit (EXIT_FAILURE);
        }
    }

  char *dirname = optind < argc ? argv[optind] : ".";
  struct stat dirstat;

  if (stat(dirname, &dirstat) != 0) {
    return EXIT_FAILURE;
  }

  struct dirent **namelist;
  int n = scandir (dirname, &namelist, NULL, filename_cmp);

  for (int i = 0; i < n; i++)
    {
      char path[MAX_PATH_LEN];
      snprintf (path, sizeof (path), "%s/%s", dirname, namelist[i]->d_name);

      struct stat st;
      lstat (path, &st);

      bool dot_dir = strcmp (namelist[i]->d_name, ".") == 0
                     || strcmp (namelist[i]->d_name, "..") == 0;

      bool hidden = namelist[i]->d_name[0] == '.';

      if (dot_dir || (!a_flag && hidden) || (s_flag && S_ISDIR (st.st_mode)))
        {
          free (namelist[i]);
          continue;
        }

      if (s_flag)
        {
          printf ("%ld ", st.st_size);
        }

      if (p_flag)
        {
          print_permissions (st.st_mode);
          printf (" ");
        }

      printf ("%s\n", namelist[i]->d_name);

      free (namelist[i]);
    }
  free (namelist);

  return EXIT_SUCCESS;
}

static void
usage (void)
{
  printf ("ls, list directory contents\n");
  printf ("usage: ls [FLAG ...] [DIR]\n");
  printf ("FLAG is one or more of:\n");
  printf ("  -a       list all files (even hidden ones)\n");
  printf ("  -p       list permission bitmask\n");
  printf ("  -s       list file sizes\n");
  printf ("If no DIR specified, list current directory contents.\n\n");
  printf ("Files must be sorted alphabetically, case insensitive.\n");
  printf ("Leading dots should be ignored when sorting.\n\n");
  printf ("With the -s flag, do not show entries for subdirectories.\n");
  printf ("Permission bitmasks are 10-character strings such as:\n");
  printf ("  -rwxr-x---\n\n");
  printf (
      "The first character is d for directories and - for regular files.\n\n");
  printf ("Do not show the \".\" or \"..\" directory entries.\n");
}