//! 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> {
        std::env::home_dir()
    }
    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")),
    }
}
