// Copyright 2022 Google LLC
// Copyright 2026 Bradford Hovinen <bradford@hovinen.me>
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::description::Description;
use crate::matcher::{Describable, Matcher, MatcherResult};
use std::fmt::Debug;

/// Matches an `Option` containing `None`.
///
/// ```
/// # use test_that::prelude::*;
/// # fn should_pass() -> TestResult<()> {
/// verify_that!(None::<()>, none())?;   // Passes
/// #     Ok(())
/// # }
/// # fn should_fail() -> TestResult<()> {
/// verify_that!(Some("Some value"), none())?;  // Fails
/// #     Ok(())
/// # }
/// # should_pass().unwrap();
/// # should_fail().unwrap_err();
/// ```
pub fn none() -> __internal::NoneMatcher {
    __internal::NoneMatcher
}

pub mod __internal {
    use super::*;

    #[doc(hidden)]
    pub struct NoneMatcher;

    impl<T: Debug> Matcher<Option<T>> for NoneMatcher {
        fn matches(&self, actual: &Option<T>) -> MatcherResult {
            (actual.is_none()).into()
        }
    }

    impl Describable for NoneMatcher {
        fn describe(&self, matcher_result: MatcherResult) -> Description {
            match matcher_result {
                MatcherResult::Match => "is none".into(),
                MatcherResult::NoMatch => "is some(_)".into(),
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::none;
    use crate::matcher::{Matcher, MatcherResult};
    use crate::prelude::*;

    #[test]
    fn none_matches_option_with_none() -> TestResult<()> {
        let matcher = none();

        let result = matcher.matches(&None::<i32>);

        verify_that!(result, eq(MatcherResult::Match))
    }

    #[test]
    fn none_does_not_match_option_with_value() -> TestResult<()> {
        let matcher = none();

        let result = matcher.matches(&Some(0));

        verify_that!(result, eq(MatcherResult::NoMatch))
    }
}
