use std::collections::HashMap;
use std::sync::Arc;
use std::sync::atomic::AtomicI64;
use std::sync::atomic::Ordering;

use codex_app_server_protocol::JSONRPCErrorError;
use codex_app_server_protocol::RequestId;
use codex_app_server_protocol::Result;
use codex_app_server_protocol::ServerNotification;
use codex_app_server_protocol::ServerRequest;
use codex_app_server_protocol::ServerRequestPayload;
use serde::Serialize;
use tokio::sync::Mutex;
use tokio::sync::mpsc;
use tokio::sync::oneshot;
use tracing::warn;

use crate::error_code::INTERNAL_ERROR_CODE;

#[cfg(test)]
use codex_protocol::account::PlanType;

/// Stable identifier for a transport connection.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub(crate) struct ConnectionId(pub(crate) u64);

/// Stable identifier for a client request scoped to a transport connection.
#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub(crate) struct ConnectionRequestId {
    pub(crate) connection_id: ConnectionId,
    pub(crate) request_id: RequestId,
}

#[derive(Debug, Clone)]
pub(crate) enum OutgoingEnvelope {
    ToConnection {
        connection_id: ConnectionId,
        message: OutgoingMessage,
    },
    Broadcast {
        message: OutgoingMessage,
    },
}

/// Sends messages to the client and manages request callbacks.
pub(crate) struct OutgoingMessageSender {
    next_server_request_id: AtomicI64,
    sender: mpsc::Sender<OutgoingEnvelope>,
    request_id_to_callback: Mutex<HashMap<RequestId, oneshot::Sender<Result>>>,
}

#[derive(Clone)]
pub(crate) struct ThreadScopedOutgoingMessageSender {
    outgoing: Arc<OutgoingMessageSender>,
    connection_ids: Arc<Vec<ConnectionId>>,
}

impl ThreadScopedOutgoingMessageSender {
    pub(crate) fn new(
        outgoing: Arc<OutgoingMessageSender>,
        connection_ids: Vec<ConnectionId>,
    ) -> Self {
        Self {
            outgoing,
            connection_ids: Arc::new(connection_ids),
        }
    }

    pub(crate) async fn send_request(
        &self,
        payload: ServerRequestPayload,
    ) -> oneshot::Receiver<Result> {
        if self.connection_ids.is_empty() {
            let (_tx, rx) = oneshot::channel();
            return rx;
        }
        self.outgoing
            .send_request_to_connections(self.connection_ids.as_slice(), payload)
            .await
    }

    pub(crate) async fn send_server_notification(&self, notification: ServerNotification) {
        if self.connection_ids.is_empty() {
            return;
        }
        self.outgoing
            .send_server_notification_to_connections(self.connection_ids.as_slice(), notification)
            .await;
    }

    pub(crate) async fn send_response<T: Serialize>(
        &self,
        request_id: ConnectionRequestId,
        response: T,
    ) {
        self.outgoing.send_response(request_id, response).await;
    }

    pub(crate) async fn send_error(
        &self,
        request_id: ConnectionRequestId,
        error: JSONRPCErrorError,
    ) {
        self.outgoing.send_error(request_id, error).await;
    }
}

impl OutgoingMessageSender {
    pub(crate) fn new(sender: mpsc::Sender<OutgoingEnvelope>) -> Self {
        Self {
            next_server_request_id: AtomicI64::new(0),
            sender,
            request_id_to_callback: Mutex::new(HashMap::new()),
        }
    }

    pub(crate) async fn send_request_to_connections(
        &self,
        connection_ids: &[ConnectionId],
        request: ServerRequestPayload,
    ) -> oneshot::Receiver<Result> {
        let (_id, rx) = self
            .send_request_with_id_to_connections(connection_ids, request)
            .await;
        rx
    }

    pub(crate) async fn send_request_with_id(
        &self,
        request: ServerRequestPayload,
    ) -> (RequestId, oneshot::Receiver<Result>) {
        self.send_request_with_id_to_connections(&[], request).await
    }

    async fn send_request_with_id_to_connections(
        &self,
        connection_ids: &[ConnectionId],
        request: ServerRequestPayload,
    ) -> (RequestId, oneshot::Receiver<Result>) {
        let id = RequestId::Integer(self.next_server_request_id.fetch_add(1, Ordering::Relaxed));
        let outgoing_message_id = id.clone();
        let (tx_approve, rx_approve) = oneshot::channel();
        {
            let mut request_id_to_callback = self.request_id_to_callback.lock().await;
            request_id_to_callback.insert(id, tx_approve);
        }

        let outgoing_message =
            OutgoingMessage::Request(request.request_with_id(outgoing_message_id.clone()));
        let send_result = if connection_ids.is_empty() {
            self.sender
                .send(OutgoingEnvelope::Broadcast {
                    message: outgoing_message,
                })
                .await
        } else {
            let mut send_error = None;
            for connection_id in connection_ids {
                if let Err(err) = self
                    .sender
                    .send(OutgoingEnvelope::ToConnection {
                        connection_id: *connection_id,
                        message: outgoing_message.clone(),
                    })
                    .await
                {
                    send_error = Some(err);
                    break;
                }
            }
            match send_error {
                Some(err) => Err(err),
                None => Ok(()),
            }
        };

        if let Err(err) = send_result {
            warn!("failed to send request {outgoing_message_id:?} to client: {err:?}");
            let mut request_id_to_callback = self.request_id_to_callback.lock().await;
            request_id_to_callback.remove(&outgoing_message_id);
        }
        (outgoing_message_id, rx_approve)
    }

    pub(crate) async fn notify_client_response(&self, id: RequestId, result: Result) {
        let entry = {
            let mut request_id_to_callback = self.request_id_to_callback.lock().await;
            request_id_to_callback.remove_entry(&id)
        };

        match entry {
            Some((id, sender)) => {
                if let Err(err) = sender.send(result) {
                    warn!("could not notify callback for {id:?} due to: {err:?}");
                }
            }
            None => {
                warn!("could not find callback for {id:?}");
            }
        }
    }

    pub(crate) async fn notify_client_error(&self, id: RequestId, error: JSONRPCErrorError) {
        let entry = {
            let mut request_id_to_callback = self.request_id_to_callback.lock().await;
            request_id_to_callback.remove_entry(&id)
        };

        match entry {
            Some((id, _sender)) => {
                warn!("client responded with error for {id:?}: {error:?}");
            }
            None => {
                warn!("could not find callback for {id:?}");
            }
        }
    }

    pub(crate) async fn cancel_request(&self, id: &RequestId) -> bool {
        let entry = {
            let mut request_id_to_callback = self.request_id_to_callback.lock().await;
            request_id_to_callback.remove_entry(id)
        };
        entry.is_some()
    }

    pub(crate) async fn send_response<T: Serialize>(
        &self,
        request_id: ConnectionRequestId,
        response: T,
    ) {
        match serde_json::to_value(response) {
            Ok(result) => {
                let outgoing_message = OutgoingMessage::Response(OutgoingResponse {
                    id: request_id.request_id,
                    result,
                });
                if let Err(err) = self
                    .sender
                    .send(OutgoingEnvelope::ToConnection {
                        connection_id: request_id.connection_id,
                        message: outgoing_message,
                    })
                    .await
                {
                    warn!("failed to send response to client: {err:?}");
                }
            }
            Err(err) => {
                self.send_error(
                    request_id,
                    JSONRPCErrorError {
                        code: INTERNAL_ERROR_CODE,
                        message: format!("failed to serialize response: {err}"),
                        data: None,
                    },
                )
                .await;
            }
        }
    }

    pub(crate) async fn send_server_notification(&self, notification: ServerNotification) {
        self.send_server_notification_to_connections(&[], notification)
            .await;
    }

    pub(crate) async fn send_server_notification_to_connections(
        &self,
        connection_ids: &[ConnectionId],
        notification: ServerNotification,
    ) {
        let outgoing_message = OutgoingMessage::AppServerNotification(notification);
        if connection_ids.is_empty() {
            if let Err(err) = self
                .sender
                .send(OutgoingEnvelope::Broadcast {
                    message: outgoing_message,
                })
                .await
            {
                warn!("failed to send server notification to client: {err:?}");
            }
            return;
        }
        for connection_id in connection_ids {
            if let Err(err) = self
                .sender
                .send(OutgoingEnvelope::ToConnection {
                    connection_id: *connection_id,
                    message: outgoing_message.clone(),
                })
                .await
            {
                warn!("failed to send server notification to client: {err:?}");
            }
        }
    }

    pub(crate) async fn send_notification_to_connections(
        &self,
        connection_ids: &[ConnectionId],
        notification: OutgoingNotification,
    ) {
        let outgoing_message = OutgoingMessage::Notification(notification);
        if connection_ids.is_empty() {
            if let Err(err) = self
                .sender
                .send(OutgoingEnvelope::Broadcast {
                    message: outgoing_message,
                })
                .await
            {
                warn!("failed to send notification to client: {err:?}");
            }
            return;
        }
        for connection_id in connection_ids {
            if let Err(err) = self
                .sender
                .send(OutgoingEnvelope::ToConnection {
                    connection_id: *connection_id,
                    message: outgoing_message.clone(),
                })
                .await
            {
                warn!("failed to send notification to client: {err:?}");
            }
        }
    }

    pub(crate) async fn send_error(
        &self,
        request_id: ConnectionRequestId,
        error: JSONRPCErrorError,
    ) {
        let outgoing_message = OutgoingMessage::Error(OutgoingError {
            id: request_id.request_id,
            error,
        });
        if let Err(err) = self
            .sender
            .send(OutgoingEnvelope::ToConnection {
                connection_id: request_id.connection_id,
                message: outgoing_message,
            })
            .await
        {
            warn!("failed to send error to client: {err:?}");
        }
    }
}

/// Outgoing message from the server to the client.
#[derive(Debug, Clone, Serialize)]
#[serde(untagged)]
pub(crate) enum OutgoingMessage {
    Request(ServerRequest),
    Notification(OutgoingNotification),
    /// AppServerNotification is specific to the case where this is run as an
    /// "app server" as opposed to an MCP server.
    AppServerNotification(ServerNotification),
    Response(OutgoingResponse),
    Error(OutgoingError),
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingNotification {
    pub method: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub params: Option<serde_json::Value>,
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingResponse {
    pub id: RequestId,
    pub result: Result,
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingError {
    pub error: JSONRPCErrorError,
    pub id: RequestId,
}

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

    use codex_app_server_protocol::AccountLoginCompletedNotification;
    use codex_app_server_protocol::AccountRateLimitsUpdatedNotification;
    use codex_app_server_protocol::AccountUpdatedNotification;
    use codex_app_server_protocol::AuthMode;
    use codex_app_server_protocol::ConfigWarningNotification;
    use codex_app_server_protocol::LoginChatGptCompleteNotification;
    use codex_app_server_protocol::RateLimitSnapshot;
    use codex_app_server_protocol::RateLimitWindow;
    use pretty_assertions::assert_eq;
    use serde_json::json;
    use tokio::time::timeout;
    use uuid::Uuid;

    use super::*;

    #[test]
    fn verify_server_notification_serialization() {
        let notification =
            ServerNotification::LoginChatGptComplete(LoginChatGptCompleteNotification {
                login_id: Uuid::nil(),
                success: true,
                error: None,
            });

        let jsonrpc_notification = OutgoingMessage::AppServerNotification(notification);
        assert_eq!(
            json!({
                "method": "loginChatGptComplete",
                "params": {
                    "loginId": Uuid::nil(),
                    "success": true,
                    "error": null,
                },
            }),
            serde_json::to_value(jsonrpc_notification)
                .expect("ensure the strum macros serialize the method field correctly"),
            "ensure the strum macros serialize the method field correctly"
        );
    }

    #[test]
    fn verify_account_login_completed_notification_serialization() {
        let notification =
            ServerNotification::AccountLoginCompleted(AccountLoginCompletedNotification {
                login_id: Some(Uuid::nil().to_string()),
                success: true,
                error: None,
            });

        let jsonrpc_notification = OutgoingMessage::AppServerNotification(notification);
        assert_eq!(
            json!({
                "method": "account/login/completed",
                "params": {
                    "loginId": Uuid::nil().to_string(),
                    "success": true,
                    "error": null,
                },
            }),
            serde_json::to_value(jsonrpc_notification)
                .expect("ensure the notification serializes correctly"),
            "ensure the notification serializes correctly"
        );
    }

    #[test]
    fn verify_account_rate_limits_notification_serialization() {
        let notification =
            ServerNotification::AccountRateLimitsUpdated(AccountRateLimitsUpdatedNotification {
                rate_limits: RateLimitSnapshot {
                    limit_id: Some("codex".to_string()),
                    limit_name: None,
                    primary: Some(RateLimitWindow {
                        used_percent: 25,
                        window_duration_mins: Some(15),
                        resets_at: Some(123),
                    }),
                    secondary: None,
                    credits: None,
                    plan_type: Some(PlanType::Plus),
                },
            });

        let jsonrpc_notification = OutgoingMessage::AppServerNotification(notification);
        assert_eq!(
            json!({
                "method": "account/rateLimits/updated",
                "params": {
                        "rateLimits": {
                        "limitId": "codex",
                        "limitName": null,
                        "primary": {
                            "usedPercent": 25,
                            "windowDurationMins": 15,
                            "resetsAt": 123
                        },
                        "secondary": null,
                        "credits": null,
                        "planType": "plus"
                    }
                },
            }),
            serde_json::to_value(jsonrpc_notification)
                .expect("ensure the notification serializes correctly"),
            "ensure the notification serializes correctly"
        );
    }

    #[test]
    fn verify_account_updated_notification_serialization() {
        let notification = ServerNotification::AccountUpdated(AccountUpdatedNotification {
            auth_mode: Some(AuthMode::ApiKey),
        });

        let jsonrpc_notification = OutgoingMessage::AppServerNotification(notification);
        assert_eq!(
            json!({
                "method": "account/updated",
                "params": {
                    "authMode": "apikey"
                },
            }),
            serde_json::to_value(jsonrpc_notification)
                .expect("ensure the notification serializes correctly"),
            "ensure the notification serializes correctly"
        );
    }

    #[test]
    fn verify_config_warning_notification_serialization() {
        let notification = ServerNotification::ConfigWarning(ConfigWarningNotification {
            summary: "Config error: using defaults".to_string(),
            details: Some("error loading config: bad config".to_string()),
            path: None,
            range: None,
        });

        let jsonrpc_notification = OutgoingMessage::AppServerNotification(notification);
        assert_eq!(
            json!( {
                "method": "configWarning",
                "params": {
                    "summary": "Config error: using defaults",
                    "details": "error loading config: bad config",
                },
            }),
            serde_json::to_value(jsonrpc_notification)
                .expect("ensure the notification serializes correctly"),
            "ensure the notification serializes correctly"
        );
    }

    #[tokio::test]
    async fn send_response_routes_to_target_connection() {
        let (tx, mut rx) = mpsc::channel::<OutgoingEnvelope>(4);
        let outgoing = OutgoingMessageSender::new(tx);
        let request_id = ConnectionRequestId {
            connection_id: ConnectionId(42),
            request_id: RequestId::Integer(7),
        };

        outgoing
            .send_response(request_id.clone(), json!({ "ok": true }))
            .await;

        let envelope = timeout(Duration::from_secs(1), rx.recv())
            .await
            .expect("should receive envelope before timeout")
            .expect("channel should contain one message");

        match envelope {
            OutgoingEnvelope::ToConnection {
                connection_id,
                message,
            } => {
                assert_eq!(connection_id, ConnectionId(42));
                let OutgoingMessage::Response(response) = message else {
                    panic!("expected response message");
                };
                assert_eq!(response.id, request_id.request_id);
                assert_eq!(response.result, json!({ "ok": true }));
            }
            other => panic!("expected targeted response envelope, got: {other:?}"),
        }
    }

    #[tokio::test]
    async fn send_error_routes_to_target_connection() {
        let (tx, mut rx) = mpsc::channel::<OutgoingEnvelope>(4);
        let outgoing = OutgoingMessageSender::new(tx);
        let request_id = ConnectionRequestId {
            connection_id: ConnectionId(9),
            request_id: RequestId::Integer(3),
        };
        let error = JSONRPCErrorError {
            code: INTERNAL_ERROR_CODE,
            message: "boom".to_string(),
            data: None,
        };

        outgoing.send_error(request_id.clone(), error.clone()).await;

        let envelope = timeout(Duration::from_secs(1), rx.recv())
            .await
            .expect("should receive envelope before timeout")
            .expect("channel should contain one message");

        match envelope {
            OutgoingEnvelope::ToConnection {
                connection_id,
                message,
            } => {
                assert_eq!(connection_id, ConnectionId(9));
                let OutgoingMessage::Error(outgoing_error) = message else {
                    panic!("expected error message");
                };
                assert_eq!(outgoing_error.id, RequestId::Integer(3));
                assert_eq!(outgoing_error.error, error);
            }
            other => panic!("expected targeted error envelope, got: {other:?}"),
        }
    }
}