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

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

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

impl SimpleStorage {
  #[must_use]
  pub const fn new(base: PathBuf) -> Self {
    Self(base)
  }

  fn get_path(&self, date: Option<u64>) -> PathBuf {
    match date {
      Some(d) => self.0.join(d.to_string()),
      None => self.0.clone(),
    }
  }
}

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

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

  fn recent_date(&self) -> Result<u64, Box<dyn Error>> {
    let dir = self.get_path(None);
    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())
  }
}