roundabout

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

use serde::{Serialize, de::DeserializeOwned};

use crate::{client::Flock, paths};

fn path(name: &str) -> PathBuf {

    paths::state_dir().join(format!("{name}.json"))

}

pub fn load<T: DeserializeOwned + Default>(name: &str) -> T {

    fs::read(path(name))

        .ok()

        .and_then(|b| serde_json::from_slice(&b).ok())

        .unwrap_or_default()

}

/// readers skip the lock, the rename keeps them from seeing half a file

pub fn update<T, R>(name: &str, f: impl FnOnce(&mut T) -> R) -> io::Result<R>

where

    T: Serialize + DeserializeOwned + Default,

{

    let lock = fs::OpenOptions::new()

        .create(true)

        .truncate(false)

        .write(true)

        .open(paths::state_dir().join(format!("{name}.lock")))?;

    let _guard = Flock::exclusive(lock)?;

    let mut value = load(name);

    let out = f(&mut value);

    let tmp = path(&format!("{name}.tmp"));

    fs::write(&tmp, serde_json::to_vec(&value)?)?;

    fs::rename(tmp, path(name))?;

    Ok(out)

}