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

use clap::Parser;
use rand::distributions::{Alphanumeric, DistString};

fn rename_or_copy(from: impl AsRef<Path>, to: impl AsRef<Path>) -> io::Result<()> {
    match fs::rename(&from, &to) {
        Ok(result) => Ok(result),
        Err(_) => {
            fs::copy(&from, &to)?;
            fs::remove_file(from)?;
            Ok(())
        }
    }
}

fn rand_string(len: usize) -> String {
    Alphanumeric.sample_string(&mut rand::thread_rng(), len)
}

fn mktemp(len: usize) -> PathBuf {
    let mut temp = env::temp_dir();
    temp.push(format!("tmp.{}", rand_string(len)));
    temp
}

#[derive(Parser, Debug)]
#[command(version, about, long_about = None)]
struct Args {
    first: String,
    second: String,
}

fn main() -> io::Result<()> {
    let args = Args::parse();
    let temp = mktemp(10);
    let cwd = env::current_dir()?;

    let first = Path::join(&cwd, args.first);
    let second = Path::join(&cwd, args.second);

    rename_or_copy(&first, &temp)?;
    rename_or_copy(&second, &first)?;
    rename_or_copy(&temp, &second)?;

    Ok(())
}