//! Lower-level utilities for mocking the process environment.

use std::{

    ffi::OsString,

    io,

    path::{Path, PathBuf},

};

/// Permits parameterizing the home functions via the _from variants - used for

/// in-process unit testing by rustup.

pub trait Env {

    /// Return the path to the users home dir, or None if any error occurs:

    /// see `home_inner`.

    fn home_dir(&self) -> Option<PathBuf>;

    /// Return the current working directory.

    fn current_dir(&self) -> io::Result<PathBuf>;

    /// Get an environment variable, as per `std::env::var_os`.

    fn var_os(&self, key: &str) -> Option<OsString>;

}

/// Implements Env for the OS context, both Unix style and Windows.

///

/// This is trait permits in-process testing by providing a control point to

/// allow in-process divergence on what is normally process wide state.

///

/// Implementations should be provided by whatever testing framework the caller

/// is using. Code that is not performing in-process threaded testing requiring

/// isolated rustup/cargo directories does not need this trait or the _from

/// functions.

pub struct OsEnv;

impl Env for OsEnv {

    fn home_dir(&self) -> Option<PathBuf> {

        crate::home_dir_inner()

    }

    fn current_dir(&self) -> io::Result<PathBuf> {

        std::env::current_dir()

    }

    fn var_os(&self, key: &str) -> Option<OsString> {

        std::env::var_os(key)

    }

}

pub const OS_ENV: OsEnv = OsEnv {};

/// Returns the path of the current user's home directory from [`Env::home_dir`].

pub fn home_dir_with_env(env: &dyn Env) -> Option<PathBuf> {

    env.home_dir()

}

/// Variant of `cargo_home` where the environment source is parameterized.

///

/// This is

/// specifically to support in-process testing scenarios as environment

/// variables and user home metadata are normally process global state. See the

/// [`Env`] trait.

pub fn cargo_home_with_env(env: &dyn Env) -> io::Result<PathBuf> {

    let cwd = env.current_dir()?;

    cargo_home_with_cwd_env(env, &cwd)

}

/// Variant of `cargo_home_with_cwd` where the environment source is

/// parameterized.

///

/// This is specifically to support in-process testing scenarios

/// as environment variables and user home metadata are normally process global

/// state. See the `OsEnv` trait.

pub fn cargo_home_with_cwd_env(env: &dyn Env, cwd: &Path) -> io::Result<PathBuf> {

    match env.var_os("CARGO_HOME").filter(|h| !h.is_empty()) {

        Some(home) => {

            let home = PathBuf::from(home);

            if home.is_absolute() {

                Ok(home)

            } else {

                Ok(cwd.join(&home))

            }

        }

        _ => home_dir_with_env(env)

            .map(|p| p.join(".cargo"))

            .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "could not find cargo home dir")),

    }

}

/// Variant of `cargo_home_with_cwd` where the environment source is

/// parameterized.

///

/// This is specifically to support in-process testing scenarios

/// as environment variables and user home metadata are normally process global

/// state. See the `OsEnv` trait.

pub fn rustup_home_with_env(env: &dyn Env) -> io::Result<PathBuf> {

    let cwd = env.current_dir()?;

    rustup_home_with_cwd_env(env, &cwd)

}

/// Variant of `cargo_home_with_cwd` where the environment source is

/// parameterized.

///

/// This is specifically to support in-process testing scenarios

/// as environment variables and user home metadata are normally process global

/// state. See the `OsEnv` trait.

pub fn rustup_home_with_cwd_env(env: &dyn Env, cwd: &Path) -> io::Result<PathBuf> {

    match env.var_os("RUSTUP_HOME").filter(|h| !h.is_empty()) {

        Some(home) => {

            let home = PathBuf::from(home);

            if home.is_absolute() {

                Ok(home)

            } else {

                Ok(cwd.join(&home))

            }

        }

        _ => home_dir_with_env(env)

            .map(|d| d.join(".rustup"))

            .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "could not find rustup home dir")),

    }

}