#![deny(missing_docs)]
//! This crate is for setting environment variables temporarily.
//!
//! It is useful for testing with different environment variables that should not interfere.
//!
//! # Examples
//!
//! ```rust
//! temp_env::with_var("MY_ENV_VAR", Some("production"), || {
//!     // Run some code where `MY_ENV_VAR` set to `"production"`.
//! });
//!
//!
//! temp_env::with_vars(
//!     vec![
//!         ("FIRST_VAR", Some("Hello")),
//!         ("SECOND_VAR", Some("World!")),
//!     ],
//!     || {
//!         // Run some code where `FIRST_VAR` is set to `"Hello"` and `SECOND_VAR` is set to
//!         // `"World!"`.
//!     }
//! );
//!
//! temp_env::with_vars(
//!     vec![
//!         ("FIRST_VAR", Some("Hello")),
//!         ("SECOND_VAR", None),
//!     ],
//!     || {
//!         // Run some code where `FIRST_VAR` is set to `"Hello"` and `SECOND_VAR` is unset (even if
//!         // it was set before)
//!     }
//! );

use std::collections::HashMap;
use std::env;
use std::ffi::OsStr;
use std::hash::Hash;
use std::panic::{self, RefUnwindSafe, UnwindSafe};
use std::sync::Mutex;

use once_cell::sync::Lazy;

/// Make sure that the environment isn't modified concurrently.
static SERIAL_TEST: Lazy<Mutex<()>> = Lazy::new(Default::default);

/// Sets a single environment variable for the duration of the closure.
///
/// The previous values are restored when the closure completes or panics, before unwinding the
/// panic.
///
/// If `value` is set to `None`, then the environment variable is unset.
pub fn with_var<K, V, F>(key: K, value: Option<V>, closure: F)
where
    K: AsRef<OsStr> + Clone + Eq + Hash,
    V: AsRef<OsStr> + Clone,
    F: Fn() + UnwindSafe + RefUnwindSafe,
{
    with_vars(vec![(key, value)], closure)
}

/// Sets environment variables for the duration of the closure.
///
/// The previous values are restored when the closure completes or panics, before unwinding the
/// panic.
///
/// If a `value` is set to `None`, then the environment variable is unset.
///
/// If the variable with the same name is set multiple times, the last one wins.
pub fn with_vars<K, V, F>(kvs: Vec<(K, Option<V>)>, closure: F)
where
    K: AsRef<OsStr> + Clone + Eq + Hash,
    V: AsRef<OsStr> + Clone,
    F: Fn() + UnwindSafe + RefUnwindSafe,
{
    let guard = SERIAL_TEST.lock().unwrap();
    let mut old_kvs: HashMap<K, Option<String>> = HashMap::new();
    for (key, value) in kvs {
        // If the same key is given several times, the original/old value is only correct before
        // the environment was updated.
        if !old_kvs.contains_key(&key) {
            let old_value = env::var(&key).ok();
            old_kvs.insert(key.clone(), old_value);
        }
        update_env(&key, value);
    }

    match panic::catch_unwind(|| {
        closure();
    }) {
        Ok(_) => {
            for (key, value) in old_kvs {
                update_env(key, value);
            }
        }
        Err(err) => {
            for (key, value) in old_kvs {
                update_env(key, value);
            }
            drop(guard);
            panic::resume_unwind(err);
        }
    };
}

fn update_env<K, V>(key: K, value: Option<V>)
where
    K: AsRef<OsStr>,
    V: AsRef<OsStr>,
{
    match value {
        Some(v) => env::set_var(key, v),
        None => env::remove_var(key),
    }
}

// Make sure that all tests use independent environment variables, so that they don't interfere if
// run in parallel.
#[cfg(test)]
mod tests {
    use std::{env, panic};

    /// Test whether setting a variable is correctly undone.
    #[test]
    fn test_with_var_set() {
        let hello_not_set = env::var("HELLO");
        assert!(hello_not_set.is_err(), "`HELLO` must not be set.");

        crate::with_var("HELLO", Some("world!"), || {
            let hello_is_set = env::var("HELLO").unwrap();
            assert_eq!(hello_is_set, "world!", "`HELLO` must be set to \"world!\".");
        });

        let hello_not_set_after = env::var("HELLO");
        assert!(hello_not_set_after.is_err(), "`HELLO` must not be set.");
    }

    /// Test whether unsetting a variable is correctly undone.
    #[test]
    fn test_with_var_unset() {
        env::set_var("FOO", "bar");
        let foo_is_set = env::var("FOO").unwrap();
        assert_eq!(foo_is_set, "bar", "`FOO` must be set to \"bar\".");

        crate::with_var("FOO", None::<&str>, || {
            let foo_not_set = env::var("FOO");
            assert!(foo_not_set.is_err(), "`FOO` must not be set.");
        });

        let foo_is_set_after = env::var("FOO").unwrap();
        assert_eq!(foo_is_set_after, "bar", "`FOO` must be set to \"bar\".");
    }

    /// Test whether overriding an existing variable is correctly undone.
    #[test]
    fn test_with_var_override() {
        env::set_var("BLAH", "blub");
        let blah_is_set = env::var("BLAH").unwrap();
        assert_eq!(blah_is_set, "blub", "`BLAH` must be set to \"blah\".");

        crate::with_var("BLAH", Some("new"), || {
            let blah_is_set_new = env::var("BLAH").unwrap();
            assert_eq!(blah_is_set_new, "new", "`BLAH` must be set to \"newb\".");
        });

        let blah_is_set_after = env::var("BLAH").unwrap();
        assert_eq!(
            blah_is_set_after, "blub",
            "`BLAH` must be set to \"blubr\"."
        );
    }

    /// Test whether overriding a variable is correctly undone in case of a panic.
    #[test]
    fn test_with_var_panic() {
        env::set_var("PANIC", "panic");
        let panic_is_set = env::var("PANIC").unwrap();
        assert_eq!(panic_is_set, "panic", "`PANIC` must be set to \"panic\".");

        let did_panic = panic::catch_unwind(|| {
            crate::with_var("PANIC", Some("don't panic"), || {
                let panic_is_set_new = env::var("PANIC").unwrap();
                assert_eq!(
                    panic_is_set_new, "don't panic",
                    "`PANIC` must be set to \"don't panic\"."
                );
                panic!("abort this closure with a panic.");
            });
        });

        assert!(did_panic.is_err(), "The closure must panic.");
        let panic_is_set_after = env::var("PANIC").unwrap();
        assert_eq!(
            panic_is_set_after, "panic",
            "`PANIC` must be set to \"panic\"."
        );
    }

    /// Test whether setting multiple variable is correctly undone.
    #[test]
    fn test_with_vars_set() {
        let one_not_set = env::var("ONE");
        assert!(one_not_set.is_err(), "`ONE` must not be set.");
        let two_not_set = env::var("TWO");
        assert!(two_not_set.is_err(), "`TWO` must not be set.");

        crate::with_vars(vec![("ONE", Some("1")), ("TWO", Some("2"))], || {
            let one_is_set = env::var("ONE").unwrap();
            assert_eq!(one_is_set, "1", "`ONE` must be set to \"1\".");
            let two_is_set = env::var("TWO").unwrap();
            assert_eq!(two_is_set, "2", "`TWO` must be set to \"2\".");
        });

        let one_not_set_after = env::var("ONE");
        assert!(one_not_set_after.is_err(), "`ONE` must not be set.");
        let two_not_set_after = env::var("TWO");
        assert!(two_not_set_after.is_err(), "`TWO` must not be set.");
    }

    /// Test whether unsetting one of the variable is correctly undone.
    #[test]
    fn test_with_vars_unset() {
        let to_be_set_not_set = env::var("TO_BE_SET");
        assert!(to_be_set_not_set.is_err(), "`TO_BE_SET` must not be set.");
        env::set_var("TO_BE_UNSET", "unset");
        let to_be_unset_is_set = env::var("TO_BE_UNSET").unwrap();
        assert_eq!(
            to_be_unset_is_set, "unset",
            "`TO_BE_UNSET` must be set to \"unset\"."
        );

        crate::with_vars(
            vec![("TO_BE_SET", Some("set")), ("TO_BE_UNSET", None::<&str>)],
            || {
                let to_be_set_is_set = env::var("TO_BE_SET").unwrap();
                assert_eq!(
                    to_be_set_is_set, "set",
                    "`TO_BE_SET` must be set to \"set\"."
                );
                let to_be_unset_not_set = env::var("TO_BE_UNSET");
                assert!(
                    to_be_unset_not_set.is_err(),
                    "`TO_BE_UNSET` must not be set."
                );
            },
        );

        let to_be_set_not_set_after = env::var("TO_BE_SET");
        assert!(
            to_be_set_not_set_after.is_err(),
            "`TO_BE_SET` must not be set."
        );
        let to_be_unset_is_set_after = env::var("TO_BE_UNSET").unwrap();
        assert_eq!(
            to_be_unset_is_set_after, "unset",
            "`TO_BE_UNSET` must be set to \"unset\"."
        );
    }

    /// Test whether overriding existing variables is correctly undone.
    #[test]
    fn test_with_vars_override() {
        env::set_var("DOIT", "doit");
        let doit_is_set = env::var("DOIT").unwrap();
        assert_eq!(doit_is_set, "doit", "`DOIT` must be set to \"doit\".");
        env::set_var("NOW", "now");
        let now_is_set = env::var("NOW").unwrap();
        assert_eq!(now_is_set, "now", "`NOW` must be set to \"now\".");

        crate::with_vars(
            vec![("DOIT", Some("other")), ("NOW", Some("value"))],
            || {
                let doit_is_set_new = env::var("DOIT").unwrap();
                assert_eq!(doit_is_set_new, "other", "`DOIT` must be set to \"other\".");
                let now_is_set_new = env::var("NOW").unwrap();
                assert_eq!(now_is_set_new, "value", "`NOW` must be set to \"value\".");
            },
        );

        let doit_is_set_after = env::var("DOIT").unwrap();
        assert_eq!(doit_is_set_after, "doit", "`DOIT` must be set to \"doit\".");
        let now_is_set_after = env::var("NOW").unwrap();
        assert_eq!(now_is_set_after, "now", "`NOW` must be set to \"now\".");
    }

    /// Test that setting the same variables twice, the latter one is used.
    #[test]
    fn test_with_vars_same_vars() {
        let override_not_set = env::var("OVERRIDE");
        assert!(override_not_set.is_err(), "`OVERRIDE` must not be set.");

        crate::with_vars(
            vec![
                ("OVERRIDE", Some("initial")),
                ("OVERRIDE", Some("override")),
            ],
            || {
                let override_is_set = env::var("OVERRIDE").unwrap();
                assert_eq!(
                    override_is_set, "override",
                    "`OVERRIDE` must be set to \"override\"."
                );
            },
        );

        let override_not_set_after = env::var("OVERRIDE");
        assert!(
            override_not_set_after.is_err(),
            "`OVERRIDE` must not be set."
        );
    }

    /// Test that unsetting and setting the same variable leads to the variable being set.
    #[test]
    fn test_with_vars_unset_set() {
        env::set_var("MY_VAR", "my_var");
        let my_var_is_set = env::var("MY_VAR").unwrap();
        assert_eq!(
            my_var_is_set, "my_var",
            "`MY_VAR` must be set to \"my_var`\"."
        );

        crate::with_vars(
            vec![("MY_VAR", None::<&str>), ("MY_VAR", Some("new value"))],
            || {
                let my_var_is_set_new = env::var("MY_VAR").unwrap();
                assert_eq!(
                    my_var_is_set_new, "new value",
                    "`MY_VAR` must be set to \"new value\"."
                );
            },
        );

        let my_var_is_set_after = env::var("MY_VAR").unwrap();
        assert_eq!(
            my_var_is_set_after, "my_var",
            "`MY_VAR` must be set to \"my_var\"."
        );
    }

    /// Test that setting and unsetting the same variable leads to the variable being unset.
    #[test]
    fn test_with_vars_set_unset() {
        let not_my_var_not_set = env::var("NOT_MY_VAR");
        assert!(not_my_var_not_set.is_err(), "`NOT_MY_VAR` must not be set.");

        crate::with_vars(
            vec![
                ("NOT_MY_VAR", Some("it is set")),
                ("NOT_MY_VAR", None::<&str>),
            ],
            || {
                let not_my_var_not_set_new = env::var("NOT_MY_VAR");
                assert!(
                    not_my_var_not_set_new.is_err(),
                    "`NOT_MY_VAR` must not be set."
                );
            },
        );

        let not_my_var_not_set_after = env::var("NOT_MY_VAR");
        assert!(
            not_my_var_not_set_after.is_err(),
            "`NOT_MY_VAR` must not be set."
        );
    }
}