#include <iostream>
#include <dirent.h>
#include <sys/stat.h>
#include <vector>
#include <queue>
#include <string>

using std::cout;
using std::vector;
using std::priority_queue;
using std::string;

//this code mainly illustrates the recursive mechanism for displaying
//the directories. But it contains enough framework to do the other things.

class Comparator {
public:  
  const bool operator() (const dirent& a, const dirent& b) {
    return a.d_name>b.d_name;
    //to sort by type, we can locate the last '.' and 
    //use the remaining part of the strings
    //for now I will leave it simple
  }

  const bool operator() (const string& s, const string& t) {
    return s>t;
  }
};

void show_info(const dirent& direntp) {
  cout<<direntp.d_name<<"\n";
  //to display -l format, do the steps in the book
}
 
const string subdir(const string& dir, const string& sub) {
  if (dir[dir.size()-1]=='/') 
    return dir+sub;
  else
    return dir+"/"+sub;
}

void do_ls(const string& dirname) {
  cout<<"\ndisplaying directory: "<<dirname<<"\n";
  DIR * dirp;
  dirent * direntp;
  if ((dirp=opendir(dirname.c_str()))==NULL)
    cout<<"cannot open "<<dirname<<"\n";
  else {
    priority_queue<dirent, vector<dirent>, Comparator> q;
    priority_queue<string, vector<string>, Comparator> dirq; 
    while ((direntp=readdir(dirp))!=NULL) {
      q.push(*direntp);
      //save directory name for recursion
      string subname(direntp->d_name);
      if (subname!="." && subname!="..") {
	struct stat info;
	subname=subdir(dirname, subname);
	lstat(subname.c_str(), &info); //using lstat to avoid stating a symlink
	if (S_ISDIR(info.st_mode))
	  dirq.push(subname);
      }
    }
    closedir(dirp);
    while (!q.empty()) {
      show_info(q.top());
      q.pop();
    }
    //recursion
    while (!dirq.empty()) {
      do_ls(dirq.top());
      dirq.pop();
    }
  }
}

int main(int ac, char ** av) {
  if (ac==1)
    do_ls(".");
  else
    while (--ac) 
      do_ls(*++av);
}