use std::env;

use std::path::{Path, PathBuf};

// Once rust 1.70 is wide-spread (Debian stable), we can use OnceLock from stdlib.

use once_cell::sync::OnceCell as OnceLock;

static DEFAULT_TEMPDIR: OnceLock<PathBuf> = OnceLock::new();

/// Override the default temporary directory (defaults to [`std::env::temp_dir`]). This function

/// changes the _global_ default temporary directory for the entire program and should not be called

/// except in exceptional cases where it's not configured correctly by the platform. Applications

/// should first check if the path returned by [`env::temp_dir`] is acceptable.

///

/// Only the first call to this function will succeed. All further calls will fail with `Err(path)`

/// where `path` is previously set default temporary directory override.

///

/// **NOTE:** This function does not check if the specified directory exists and/or is writable.

pub fn override_temp_dir(path: &Path) -> Result<(), PathBuf> {

    let mut we_set = false;

    let val = DEFAULT_TEMPDIR.get_or_init(|| {

        we_set = true;

        path.to_path_buf()

    });

    if we_set {

        Ok(())

    } else {

        Err(val.to_owned())

    }

}

/// Returns the default temporary directory, used for both temporary directories and files if no

/// directory is explicitly specified.

///

/// This function simply delegates to [`std::env::temp_dir`] unless the default temporary directory

/// has been override by a call to [`override_temp_dir`].

///

/// **NOTE:** This function does check if the returned directory exists and/or is writable.

pub fn temp_dir() -> PathBuf {

    DEFAULT_TEMPDIR

        .get()

        .map(|p| p.to_owned())

        // Don't cache this in case the user uses std::env::set to change the temporary directory.

        .unwrap_or_else(env::temp_dir)

}