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//  Copyright 2024 Foyer Project Authors
//
//  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 std::{
    fmt::Debug,
    mem::ManuallyDrop,
    ops::{Deref, DerefMut},
};

use tokio::runtime::Runtime;

/// A wrapper around [`Runtime`] that shuts down the runtime in the background when dropped.
///
/// This is necessary because directly dropping a nested runtime is not allowed in a parent runtime.
pub struct BackgroundShutdownRuntime(ManuallyDrop<Runtime>);

impl Debug for BackgroundShutdownRuntime {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_tuple("BackgroundShutdownRuntime").finish()
    }
}

impl Drop for BackgroundShutdownRuntime {
    fn drop(&mut self) {
        // Safety: The runtime is only dropped once here.
        let runtime = unsafe { ManuallyDrop::take(&mut self.0) };

        #[cfg(madsim)]
        drop(runtime);
        #[cfg(not(madsim))]
        runtime.shutdown_background();
    }
}

impl Deref for BackgroundShutdownRuntime {
    type Target = Runtime;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl DerefMut for BackgroundShutdownRuntime {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl From<Runtime> for BackgroundShutdownRuntime {
    fn from(runtime: Runtime) -> Self {
        Self(ManuallyDrop::new(runtime))
    }
}