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

use codex_core::protocol::Event;
use mcp_types::JSONRPC_VERSION;
use mcp_types::JSONRPCError;
use mcp_types::JSONRPCErrorError;
use mcp_types::JSONRPCMessage;
use mcp_types::JSONRPCNotification;
use mcp_types::JSONRPCRequest;
use mcp_types::JSONRPCResponse;
use mcp_types::RequestId;
use mcp_types::Result;
use serde::Serialize;
use tokio::sync::Mutex;
use tokio::sync::mpsc;
use tokio::sync::oneshot;
use tracing::warn;

pub(crate) struct OutgoingMessageSender {
    next_request_id: AtomicI64,
    sender: mpsc::Sender<OutgoingMessage>,
    request_id_to_callback: Mutex<HashMap<RequestId, oneshot::Sender<Result>>>,
}

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

    pub(crate) async fn send_request(
        &self,
        method: &str,
        params: Option<serde_json::Value>,
    ) -> oneshot::Receiver<Result> {
        let id = RequestId::Integer(self.next_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(OutgoingRequest {
            id: outgoing_message_id,
            method: method.to_string(),
            params,
        });
        let _ = self.sender.send(outgoing_message).await;
        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 send_response(&self, id: RequestId, result: Result) {
        let outgoing_message = OutgoingMessage::Response(OutgoingResponse { id, result });
        let _ = self.sender.send(outgoing_message).await;
    }

    pub(crate) async fn send_event_as_notification(&self, event: &Event) {
        #[expect(clippy::expect_used)]
        let params = Some(serde_json::to_value(event).expect("Event must serialize"));
        let outgoing_message = OutgoingMessage::Notification(OutgoingNotification {
            method: "codex/event".to_string(),
            params: params.clone(),
        });
        let _ = self.sender.send(outgoing_message).await;

        self.send_event_as_notification_new_schema(event, params)
            .await;
    }
    // should be backwards compatible.
    // it will replace send_event_as_notification eventually.
    async fn send_event_as_notification_new_schema(
        &self,
        event: &Event,
        params: Option<serde_json::Value>,
    ) {
        let outgoing_message = OutgoingMessage::Notification(OutgoingNotification {
            method: event.msg.to_string(),
            params,
        });
        let _ = self.sender.send(outgoing_message).await;
    }
    pub(crate) async fn send_error(&self, id: RequestId, error: JSONRPCErrorError) {
        let outgoing_message = OutgoingMessage::Error(OutgoingError { id, error });
        let _ = self.sender.send(outgoing_message).await;
    }
}

/// Outgoing message from the server to the client.
pub(crate) enum OutgoingMessage {
    Request(OutgoingRequest),
    Notification(OutgoingNotification),
    Response(OutgoingResponse),
    Error(OutgoingError),
}

impl From<OutgoingMessage> for JSONRPCMessage {
    fn from(val: OutgoingMessage) -> Self {
        use OutgoingMessage::*;
        match val {
            Request(OutgoingRequest { id, method, params }) => {
                JSONRPCMessage::Request(JSONRPCRequest {
                    jsonrpc: JSONRPC_VERSION.into(),
                    id,
                    method,
                    params,
                })
            }
            Notification(OutgoingNotification { method, params }) => {
                JSONRPCMessage::Notification(JSONRPCNotification {
                    jsonrpc: JSONRPC_VERSION.into(),
                    method,
                    params,
                })
            }
            Response(OutgoingResponse { id, result }) => {
                JSONRPCMessage::Response(JSONRPCResponse {
                    jsonrpc: JSONRPC_VERSION.into(),
                    id,
                    result,
                })
            }
            Error(OutgoingError { id, error }) => JSONRPCMessage::Error(JSONRPCError {
                jsonrpc: JSONRPC_VERSION.into(),
                id,
                error,
            }),
        }
    }
}

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