//! No-operation queue adapter implementation.
//!
//! This module provides a queue adapter that discards all work items,
//! useful for testing or when queue processing is disabled.

use async_trait::async_trait;
use std::time::Duration;
use tokio::time::sleep;

use super::adapter::QueueAdapter;
use super::error::Result;

/// No-operation queue adapter that discards all work items.
///
/// This adapter is useful for configurations where queuing is disabled
/// or as a fallback when other queue adapters fail to initialize.
/// All work items pushed to this queue are silently discarded.
///
/// # Features
///
/// - Zero resource usage
/// - Always healthy
/// - Discards all work items
/// - Never returns items from pull
///
/// # Use Cases
///
/// - Testing environments where queue processing isn't needed
/// - Graceful degradation when queue backends are unavailable
/// - Configurations where queue processing is explicitly disabled
///
/// # Examples
///
/// ```
/// use quickdid::queue::NoopQueueAdapter;
/// use quickdid::queue::QueueAdapter;
///
/// # async fn example() -> anyhow::Result<()> {
/// let queue = NoopQueueAdapter::<String>::new();
///
/// // Push is silently discarded
/// queue.push("ignored".to_string()).await?;
///
/// // Pull never returns items (blocks indefinitely)
/// // let item = queue.pull().await; // Would block forever
///
/// // Always reports healthy
/// assert!(queue.is_healthy().await);
///
/// // Always reports empty
/// assert_eq!(queue.depth().await, Some(0));
/// # Ok(())
/// # }
/// ```
pub struct NoopQueueAdapter<T>
where
    T: Send + Sync + 'static,
{
    _phantom: std::marker::PhantomData<T>,
}

impl<T> NoopQueueAdapter<T>
where
    T: Send + Sync + 'static,
{
    /// Create a new no-op queue adapter.
    ///
    /// # Examples
    ///
    /// ```
    /// use quickdid::queue::NoopQueueAdapter;
    ///
    /// let queue = NoopQueueAdapter::<String>::new();
    /// ```
    pub fn new() -> Self {
        Self {
            _phantom: std::marker::PhantomData,
        }
    }
}

impl<T> Default for NoopQueueAdapter<T>
where
    T: Send + Sync + 'static,
{
    fn default() -> Self {
        Self::new()
    }
}

#[async_trait]
impl<T> QueueAdapter<T> for NoopQueueAdapter<T>
where
    T: Send + Sync + 'static,
{
    async fn pull(&self) -> Option<T> {
        // Never returns any work - sleeps to avoid busy-waiting
        sleep(Duration::from_secs(60)).await;
        None
    }

    async fn push(&self, _work: T) -> Result<()> {
        // Silently discard the work
        Ok(())
    }

    async fn ack(&self, _item: &T) -> Result<()> {
        // No-op
        Ok(())
    }

    async fn try_push(&self, _work: T) -> Result<()> {
        // Silently discard the work
        Ok(())
    }

    async fn depth(&self) -> Option<usize> {
        // Always empty
        Some(0)
    }

    async fn is_healthy(&self) -> bool {
        // Always healthy
        true
    }
}

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

    #[tokio::test]
    async fn test_noop_queue_push() {
        let queue = NoopQueueAdapter::<String>::new();

        // Push should always succeed
        queue.push("test1".to_string()).await.unwrap();
        queue.push("test2".to_string()).await.unwrap();
        queue.push("test3".to_string()).await.unwrap();
    }

    #[tokio::test]
    async fn test_noop_queue_try_push() {
        let queue = NoopQueueAdapter::<i32>::new();

        // Try push should always succeed
        queue.try_push(1).await.unwrap();
        queue.try_push(2).await.unwrap();
        queue.try_push(3).await.unwrap();
    }

    #[tokio::test]
    async fn test_noop_queue_ack() {
        let queue = NoopQueueAdapter::<String>::new();

        // Ack should always succeed
        queue.ack(&"any".to_string()).await.unwrap();
    }

    #[tokio::test]
    async fn test_noop_queue_depth() {
        let queue = NoopQueueAdapter::<String>::new();

        // Should always report empty
        assert_eq!(queue.depth().await, Some(0));

        // Even after pushing items
        queue.push("item".to_string()).await.unwrap();
        assert_eq!(queue.depth().await, Some(0));
    }

    #[tokio::test]
    async fn test_noop_queue_health() {
        let queue = NoopQueueAdapter::<String>::new();

        // Should always be healthy
        assert!(queue.is_healthy().await);
    }

    #[tokio::test]
    async fn test_noop_queue_default() {
        let queue: NoopQueueAdapter<String> = Default::default();

        // Default instance should work normally
        queue.push("test".to_string()).await.unwrap();
        assert!(queue.is_healthy().await);
    }

    #[tokio::test(flavor = "multi_thread")]
    async fn test_noop_queue_pull_blocks() {
        use tokio::time::timeout;

        let queue = NoopQueueAdapter::<String>::new();

        // Pull should block and not return immediately
        let result = timeout(Duration::from_millis(100), queue.pull()).await;
        assert!(result.is_err(), "Pull should have timed out");
    }

    #[tokio::test]
    async fn test_noop_queue_with_custom_type() {
        use serde::{Deserialize, Serialize};

        #[derive(Debug, Clone, Serialize, Deserialize)]
        struct CustomWork {
            id: u64,
            data: Vec<String>,
        }

        let queue = NoopQueueAdapter::<CustomWork>::new();

        let work = CustomWork {
            id: 123,
            data: vec!["test".to_string()],
        };

        // Should handle custom types without issue
        queue.push(work.clone()).await.unwrap();
        queue.ack(&work).await.unwrap();
        assert_eq!(queue.depth().await, Some(0));
    }
}