use std::error::Error;
use std::fs::read_dir;
use std::str::FromStr;
use std::time::{SystemTime, UNIX_EPOCH};

pub trait Storage {
  fn write_filename(&self) -> String;
  fn read_filename(&self) -> Result<String, Box<dyn Error>>;
  fn recent_date(&self) -> Result<u64, Box<dyn Error>>;
}

#[derive(Clone)]
pub struct SimpleStorage(String, String);

impl SimpleStorage {
  pub fn new(base: String, filename: String) -> Self {
    SimpleStorage(base, filename)
  }

  fn get_path(&self, date: Option<u64>) -> String {
    match date {
      Some(d) => format!("{}/_{}/{}", self.0, self.1, d),
      None => format!("{}/_{}", self.0, self.1)
    }
  }
}

impl Storage for SimpleStorage {
  fn write_filename(&self) -> String {
    self.get_path(Some(SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs()))
  }

  fn read_filename(&self) -> Result<String, Box<dyn Error>> {
    Ok(self.get_path(Some(try!(self.recent_date()))))
  }

  fn recent_date(&self) -> Result<u64, Box<dyn Error>> {
    let dir = self.get_path(None);
    try!(read_dir(dir))
    .map(|entry| entry.ok().and_then(|e| e.file_name().into_string().ok()).and_then(|filename| u64::from_str(&filename).ok()))
    .fold(None, |maybe_newest, maybe_time| maybe_newest.into_iter().chain(maybe_time).max())
    .ok_or_else(|| "Not found".to_string().into())
  }
}