torii-core 0.5.2

use std::sync::Arc;

use async_trait::async_trait;
use tokio::sync::RwLock;

use crate::{Session, User, UserId, error::EventError, session::SessionToken};

/// Represents events that can be emitted by the event bus
///
/// Events are used to notify interested parties about changes in the system state.
/// This includes user-related events (creation, updates, deletion) and
/// session-related events (creation, deletion).
///
/// All events contain the relevant data needed to handle the event, such as
/// the affected User or Session objects.
#[derive(Debug, Clone)]
pub enum Event {
    UserCreated(User),
    UserUpdated(User),
    UserDeleted(UserId),
    SessionCreated(UserId, Session),
    SessionDeleted(UserId, SessionToken),
    SessionsCleared(UserId),
}

/// A trait for handling events emitted by the event bus
///
/// Implementors of this trait can be registered with the [`EventBus`] to receive and process events.
/// The handler is called asynchronously for each event emitted.
///
/// # Errors
///
/// Returns an [`Error`] if event handling fails. The error will be propagated back through the event bus.
///
/// # Examples
///
/// ```
/// # use torii_core::events::{Event, EventHandler};
/// # use async_trait::async_trait;
/// struct MyHandler;
///
/// #[async_trait]
/// impl EventHandler for MyHandler {
///     async fn handle(&self, event: &Event) -> Result<(), Error> {
///         // Handle the event...
///         Ok(())
///     }
/// }
/// ```
#[async_trait]
pub trait EventHandler: Send + Sync + 'static {
    async fn handle_event(&self, event: &Event) -> Result<(), EventError>;
}

/// Event bus that can emit events and register event handlers
///
/// The event bus is responsible for managing event handlers and emitting events to them.
/// It provides a simple way to register and unregister handlers, and to emit events to all registered handlers.
///
/// # Examples
///
/// ```
/// # use torii_core::events::{Event, EventBus};
/// # use async_trait::async_trait;
/// struct MyHandler;
///
/// #[async_trait]
/// impl EventHandler for MyHandler {
///     async fn handle_event(&self, event: &Event) -> Result<(), Error> {
///         // Handle the event...
///         Ok(())
///     }
/// }
///
/// let mut event_bus = EventBus::default();
/// event_bus.register(Arc::new(MyHandler));
/// event_bus.emit(&Event::UserCreated(User::builder().id(UserId::new("test")).build().unwrap())).await;
/// ```
#[derive(Clone)]
pub struct EventBus {
    handlers: Arc<RwLock<Vec<Arc<dyn EventHandler>>>>,
}

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

impl EventBus {
    /// Create a new event bus
    ///
    /// # Examples
    ///
    /// ```
    /// # use torii_core::events::EventBus;
    /// let event_bus = EventBus::new();
    /// ```
    pub fn new() -> Self {
        Self {
            handlers: Arc::new(RwLock::new(Vec::new())),
        }
    }

    /// Register an event handler with the event bus
    ///
    /// # Examples
    ///
    /// ```
    /// # use torii_core::events::{Event, EventHandler, EventBus};  
    /// # use async_trait::async_trait;
    /// struct MyHandler;
    ///
    /// #[async_trait]
    /// impl EventHandler for MyHandler {
    ///     async fn handle_event(&self, event: &Event) -> Result<(), Error> {
    ///         // Handle the event...
    ///         Ok(())
    ///     }
    /// }
    ///
    /// let mut event_bus = EventBus::default();
    /// event_bus.register(Arc::new(MyHandler));
    /// ```
    pub async fn register(&self, handler: Arc<dyn EventHandler>) {
        self.handlers.write().await.push(handler);
    }

    /// Emit an event to all registered handlers
    ///
    /// # Examples
    ///
    /// ```
    /// # use torii_core::events::{Event, EventBus};
    /// let event_bus = EventBus::default();
    /// event_bus.emit(&Event::UserCreated(User::builder().id(UserId::new("test")).build().unwrap())).await;
    /// ```
    pub async fn emit(&self, event: &Event) -> Result<(), EventError> {
        for handler in self.handlers.read().await.iter() {
            handler.handle_event(event).await?;
        }

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::session::SessionToken;
    use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};

    struct TestEventHandler {
        called: Arc<AtomicBool>,
        call_count: Arc<AtomicUsize>,
    }

    #[async_trait]
    impl EventHandler for TestEventHandler {
        async fn handle_event(&self, _event: &Event) -> Result<(), EventError> {
            self.called.store(true, Ordering::SeqCst);
            self.call_count.fetch_add(1, Ordering::SeqCst);
            Ok(())
        }
    }

    struct ErroringEventHandler;

    #[async_trait]
    impl EventHandler for ErroringEventHandler {
        async fn handle_event(&self, _event: &Event) -> Result<(), EventError> {
            Err(EventError::BusError("Test error".into()))
        }
    }

    #[tokio::test]
    async fn test_event_bus_empty() {
        let event_bus = EventBus::default();
        let test_user = User::builder()
            .id(UserId::new("test"))
            .email("test@example.com".to_string())
            .build()
            .expect("Failed to build test user");

        // Should succeed with no handlers
        event_bus
            .emit(&Event::UserCreated(test_user))
            .await
            .expect("Failed to emit event");
    }

    #[tokio::test]
    async fn test_event_bus_multiple_handlers() {
        let event_bus = EventBus::default();
        let called1 = Arc::new(AtomicBool::new(false));
        let count1 = Arc::new(AtomicUsize::new(0));
        let called2 = Arc::new(AtomicBool::new(false));
        let count2 = Arc::new(AtomicUsize::new(0));

        let handler1 = TestEventHandler {
            called: called1.clone(),
            call_count: count1.clone(),
        };
        let handler2 = TestEventHandler {
            called: called2.clone(),
            call_count: count2.clone(),
        };

        event_bus.register(Arc::new(handler1)).await;
        event_bus.register(Arc::new(handler2)).await;

        let test_user = User::builder()
            .id(UserId::new("test"))
            .email("test@example.com".to_string())
            .build()
            .expect("Failed to build test user");

        // Both handlers should be called
        event_bus
            .emit(&Event::UserCreated(test_user))
            .await
            .expect("Failed to emit event");

        assert!(
            called1.load(Ordering::SeqCst),
            "First handler was not called"
        );
        assert!(
            called2.load(Ordering::SeqCst),
            "Second handler was not called"
        );
        assert_eq!(count1.load(Ordering::SeqCst), 1);
        assert_eq!(count2.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn test_event_bus_error_propagation() {
        let event_bus = EventBus::default();
        event_bus.register(Arc::new(ErroringEventHandler)).await;

        let test_user = User::builder()
            .id(UserId::new("test"))
            .email("test@example.com".to_string())
            .build()
            .expect("Failed to build test user");

        // Should propagate error from handler
        let result = event_bus.emit(&Event::UserCreated(test_user)).await;
        assert!(result.is_err());
        assert!(matches!(result.unwrap_err(), EventError::BusError(_)));
    }

    #[tokio::test]
    async fn test_event_bus_all_event_types() {
        let event_bus = EventBus::default();
        let called = Arc::new(AtomicBool::new(false));
        let count = Arc::new(AtomicUsize::new(0));

        let handler = TestEventHandler {
            called: called.clone(),
            call_count: count.clone(),
        };
        event_bus.register(Arc::new(handler)).await;

        let test_user = User::builder()
            .id(UserId::new("test"))
            .email("test@example.com".to_string())
            .build()
            .expect("Failed to build test user");

        let test_session = Session::builder()
            .token(SessionToken::new("test"))
            .user_id(test_user.id.clone())
            .build()
            .expect("Failed to build test session");

        // Test all event types
        let events = vec![
            Event::UserCreated(test_user.clone()),
            Event::UserUpdated(test_user.clone()),
            Event::UserDeleted(test_user.id.clone()),
            Event::SessionCreated(test_user.id.clone(), test_session.clone()),
            Event::SessionDeleted(test_user.id.clone(), test_session.token.clone()),
        ];

        for event in events {
            called.store(false, Ordering::SeqCst);
            event_bus.emit(&event).await.expect("Failed to emit event");
            assert!(called.load(Ordering::SeqCst), "Handler was not called");
        }

        assert_eq!(count.load(Ordering::SeqCst), 5);
    }
}