//! Contains the events and functionality for monitoring behavior of the connection pooling of a
//! `Client`.

use serde::Deserialize;

pub use crate::cmap::options::ConnectionPoolOptions;
use crate::options::StreamAddress;

/// We implement `Deserialize` for all of the event types so that we can more easily parse the CMAP
/// spec tests. However, we have no need to parse the address field from the JSON files (if it's
/// even present). To facilitate populating the address field with an empty value when
/// deserializing, we define a private `empty_address` function that the events can specify as the
/// custom deserialization value for each address field.
fn empty_address() -> StreamAddress {
    StreamAddress {
        hostname: Default::default(),
        port: None,
    }
}

/// Event emitted when a connection pool is created.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[non_exhaustive]
pub struct PoolCreatedEvent {
    /// The address of the server that the pool's connections will connect to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,

    /// The options used for the pool.
    pub options: Option<ConnectionPoolOptions>,
}

/// Event emitted when a connection pool becomes ready.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[non_exhaustive]
pub struct PoolReadyEvent {
    /// The address of the server that the pool's connections will connect to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,
}

/// Event emitted when a connection pool is cleared.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[non_exhaustive]
pub struct PoolClearedEvent {
    /// The address of the server that the pool's connections will connect to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,
}

/// Event emitted when a connection pool is cleared.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[non_exhaustive]
pub struct PoolClosedEvent {
    /// The address of the server that the pool's connections will connect to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,
}

/// Event emitted when a connection is created.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
#[non_exhaustive]
pub struct ConnectionCreatedEvent {
    /// The address of the server that the connection will connect to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,

    /// The unique ID of the connection. This is not used for anything internally, but can be used
    /// to identify other events related to this connection.
    #[serde(default = "default_connection_id")]
    pub connection_id: u32,
}

/// Event emitted when a connection is ready to be used. This indicates that all the necessary
/// prerequisites for using a connection (handshake, authentication, etc.) have been completed.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
#[non_exhaustive]
pub struct ConnectionReadyEvent {
    /// The address of the server that the connection is connected to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,

    /// The unique ID of the connection. This is not used for anything internally, but can be used
    /// to identify other events related to this connection.
    #[serde(default = "default_connection_id")]
    pub connection_id: u32,
}

/// Event emitted when a connection is closed.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
#[non_exhaustive]
pub struct ConnectionClosedEvent {
    /// The address of the server that the connection was connected to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,

    /// The unique ID of the connection. This is not used for anything internally, but can be used
    /// to identify other events related to this connection.
    #[serde(default)]
    pub connection_id: u32,

    /// The reason that the connection was closed.
    pub reason: ConnectionClosedReason,
}

/// The reasons that a connection may be closed.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
#[non_exhaustive]
pub enum ConnectionClosedReason {
    /// The connection pool has been cleared since the connection was created.
    Stale,

    /// The connection has been available for longer than `max_idle_time` without being used.
    Idle,

    /// An error occurred while using the connection.
    Error,

    /// The connection was dropped during read or write.
    Dropped,

    /// The pool that the connection belongs to has been closed.
    PoolClosed,
}

/// Event emitted when a thread begins checking out a connection to use for an operation.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[non_exhaustive]
pub struct ConnectionCheckoutStartedEvent {
    /// The address of the server that the connection will connect to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,
}

/// Event emitted when a thread is unable to check out a connection.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[non_exhaustive]
pub struct ConnectionCheckoutFailedEvent {
    /// The address of the server that the connection would have connected to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,

    /// The reason a connection was unable to be checked out.
    pub reason: ConnectionCheckoutFailedReason,
}

/// The reasons a connection may not be able to be checked out.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
#[non_exhaustive]
pub enum ConnectionCheckoutFailedReason {
    /// The `wait_queue_timeout` has elapsed while waiting for a connection to be available.
    Timeout,

    /// An error occurred while trying to establish a connection (e.g. during the handshake or
    /// authentication).
    ConnectionError,
}

/// Event emitted when a connection is successfully checked out.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
#[non_exhaustive]
pub struct ConnectionCheckedOutEvent {
    /// The address of the server that the connection will connect to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,

    /// The unique ID of the connection. This is not used for anything internally, but can be used
    /// to identify other events related to this connection.
    #[serde(default = "default_connection_id")]
    pub connection_id: u32,
}

/// Event emitted when a connection is checked back into a connection pool.
#[derive(Clone, Debug, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
#[non_exhaustive]
pub struct ConnectionCheckedInEvent {
    /// The address of the server that the connection was connected to.
    #[serde(default = "self::empty_address")]
    #[serde(skip)]
    pub address: StreamAddress,

    /// The unique ID of the connection. This is not used for anything internally, but can be used
    /// to identify other events related to this connection.
    #[serde(default = "default_connection_id")]
    pub connection_id: u32,
}

/// The default connection ID to use for deserialization of events from test files.
/// This value will "match" any connection ID.
fn default_connection_id() -> u32 {
    42
}

/// Applications can implement this trait to specify custom logic to run on each CMAP event sent
/// by the driver.
///
/// ```rust
/// # use std::sync::Arc;
/// #
/// # use mongodb::{
/// #     error::Result,
/// #     event::cmap::{
/// #         CmapEventHandler,
/// #         ConnectionCheckoutFailedEvent
/// #     },
/// #     options::ClientOptions,
/// # };
/// # #[cfg(feature = "sync")]
/// # use mongodb::sync::Client;
/// # #[cfg(not(feature = "sync"))]
/// # use mongodb::Client;
/// #
/// struct FailedCheckoutLogger;
///
/// impl CmapEventHandler for FailedCheckoutLogger {
///     fn handle_connection_checkout_failed_event(&self, event: ConnectionCheckoutFailedEvent) {
///         eprintln!("Failed connection checkout: {:?}", event);
///     }
/// }
///
/// # fn do_stuff() -> Result<()> {
/// let handler: Arc<dyn CmapEventHandler> = Arc::new(FailedCheckoutLogger);
/// let options = ClientOptions::builder()
///                   .cmap_event_handler(handler)
///                   .build();
/// let client = Client::with_options(options)?;
///
/// // Do things with the client, and failed connection pool checkouts will be logged to stderr.
/// # Ok(())
/// # }
/// ```
pub trait CmapEventHandler: Send + Sync {
    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection pool is created.
    fn handle_pool_created_event(&self, _event: PoolCreatedEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection pool marked as ready for use.
    ///
    /// Connections may not be created by or checked out from the pool until it has been marked as
    /// ready.
    fn handle_pool_ready_event(&self, _event: PoolReadyEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection pool is cleared.
    fn handle_pool_cleared_event(&self, _event: PoolClearedEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection pool is cleared.
    fn handle_pool_closed_event(&self, _event: PoolClosedEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection is created.
    fn handle_connection_created_event(&self, _event: ConnectionCreatedEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection is ready to be used.
    fn handle_connection_ready_event(&self, _event: ConnectionReadyEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection is closed.
    fn handle_connection_closed_event(&self, _event: ConnectionClosedEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a thread begins checking out a connection to use for an operation.
    fn handle_connection_checkout_started_event(&self, _event: ConnectionCheckoutStartedEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a thread is unable to check out a connection.
    fn handle_connection_checkout_failed_event(&self, _event: ConnectionCheckoutFailedEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection is successfully checked out.
    fn handle_connection_checked_out_event(&self, _event: ConnectionCheckedOutEvent) {}

    /// A [`Client`](../../struct.Client.html) will call this method on each registered handler
    /// whenever a connection is checked back into a connection pool.
    fn handle_connection_checked_in_event(&self, _event: ConnectionCheckedInEvent) {}
}