//! Async runtime support for Ruchy
//!
//! Provides async/await functionality and Future trait integration

#![cfg(any(feature = "notebook", feature = "mcp"))]

use std::future::Future as StdFuture;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::Duration;
use tokio::time::sleep;

/// Async runtime for executing futures
pub struct AsyncRuntime {
    // In a real implementation, this would manage the executor
}

impl AsyncRuntime {
    /// Create a new async runtime
    pub fn new() -> Self {
        Self {}
    }

    /// Spawn a future on the runtime
    pub fn spawn<T>(&self, future: impl StdFuture<Output = T> + Send + 'static) -> JoinHandle<T>
    where
        T: Send + 'static,
    {
        JoinHandle {
            handle: tokio::spawn(future),
        }
    }

    /// Sleep for a duration
    pub async fn sleep(&self, duration: Duration) {
        sleep(duration).await;
    }
}

impl Default for AsyncRuntime {
    fn default() -> Self {
        Self::new()
    }
}

/// Handle to a spawned future
pub struct JoinHandle<T> {
    handle: tokio::task::JoinHandle<T>,
}

impl<T> StdFuture for JoinHandle<T> {
    type Output = T;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        match Pin::new(&mut self.handle).poll(cx) {
            Poll::Ready(Ok(value)) => Poll::Ready(value),
            Poll::Ready(Err(_)) => panic!("Task panicked"),
            Poll::Pending => Poll::Pending,
        }
    }
}

/// Ruchy's Future trait (wraps `std::future::Future`)
pub trait Future {
    type Output;

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::time::Duration;

    #[test]
    fn test_async_runtime_new() {
        let _runtime = AsyncRuntime::new();
        // Should create runtime
        // Test passes without panic;
    }

    #[test]
    fn test_async_runtime_default() {
        let _runtime = AsyncRuntime::default();
        // Should create runtime via default
        // Test passes without panic;
    }

    #[tokio::test]
    async fn test_async_runtime_sleep() {
        let runtime = AsyncRuntime::new();
        runtime.sleep(Duration::from_millis(1)).await;
        // Should sleep without panic
        // Test passes without panic;
    }

    #[tokio::test]
    async fn test_async_runtime_sleep_actually_waits() {
        // Mutation test: Verify sleep actually delays execution (not just a no-op)
        use std::time::Instant;
        let runtime = AsyncRuntime::new();
        let start = Instant::now();
        runtime.sleep(Duration::from_millis(50)).await;
        let elapsed = start.elapsed();
        assert!(
            elapsed >= Duration::from_millis(40),
            "Sleep should delay at least 40ms, got {elapsed:?}"
        );
    }

    #[tokio::test]
    async fn test_async_runtime_spawn() {
        let runtime = AsyncRuntime::new();
        let handle = runtime.spawn(async { 42 });
        let result = handle.await;
        assert_eq!(result, 42);
    }

    #[tokio::test]
    async fn test_async_runtime_spawn_multiple() {
        let runtime = AsyncRuntime::new();
        let handle1 = runtime.spawn(async { 10 });
        let handle2 = runtime.spawn(async { 20 });
        let handle3 = runtime.spawn(async { 30 });

        assert_eq!(handle1.await, 10);
        assert_eq!(handle2.await, 20);
        assert_eq!(handle3.await, 30);
    }

    #[tokio::test]
    async fn test_async_runtime_spawn_with_sleep() {
        let runtime = AsyncRuntime::new();
        let handle = runtime.spawn(async {
            sleep(Duration::from_millis(1)).await;
            "completed"
        });
        let result = handle.await;
        assert_eq!(result, "completed");
    }
}
