use std::env;
use std::fs::{self,DirEntry};
use std::io;
use std::path::Path;

fn main() -> io::Result<()> {
    let args : Vec<String> = env::args().collect();
    if args.len() == 1 {
        dfs(".", & mut "".to_string());
    }
    else {
        dfs(&args[1], & mut "".to_string());
    }
    Ok(())
}

fn dfs(path: &str,  blank: & mut String) -> io::Result<()> {
    for entry in fs::read_dir(path)? {
        let dir = entry?;
        let dir_path = dir.path();
        let this_path_str = dir_path.to_str().expect("path convert to str error");
        let this_path = Path::new(this_path_str);

        println!("{}|", &blank);
        println!("{}{:?}",&blank, dir.file_name());
        if this_path.is_dir() {
            for i in 0..dir.file_name().len() {
                blank.push(' ');
            }
            dfs(this_path_str, blank);
            for i in 0..dir.file_name().len() {
                blank.pop();
            }
        }
    }
    Ok(())
}