pub mod builder;
pub mod channel;
pub mod pubsub_service;
mod response_queue;
pub mod service;

use std::{collections::HashMap, sync::Arc};

use log::{debug, error, trace, warn};

use karyon_core::async_util::{select, Either, TaskGroup, TaskResult};
use karyon_net::{Conn, Endpoint, Listener};

use crate::{message, Error, PubSubRPCService, RPCService, Result};

use channel::Channel;
use response_queue::ResponseQueue;

pub const INVALID_REQUEST_ERROR_MSG: &str = "Invalid request";
pub const FAILED_TO_PARSE_ERROR_MSG: &str = "Failed to parse";
pub const METHOD_NOT_FOUND_ERROR_MSG: &str = "Method not found";
pub const UNSUPPORTED_JSONRPC_VERSION: &str = "Unsupported jsonrpc version";

struct NewRequest {
    srvc_name: String,
    method_name: String,
    msg: message::Request,
}

enum SanityCheckResult {
    NewReq(NewRequest),
    ErrRes(message::Response),
}

/// Represents an RPC server
pub struct Server {
    listener: Listener<serde_json::Value>,
    task_group: TaskGroup,
    services: HashMap<String, Arc<dyn RPCService + 'static>>,
    pubsub_services: HashMap<String, Arc<dyn PubSubRPCService + 'static>>,
}

impl Server {
    /// Returns the local endpoint.
    pub fn local_endpoint(&self) -> Result<Endpoint> {
        self.listener.local_endpoint().map_err(Error::from)
    }

    /// Starts the RPC server
    pub fn start(self: &Arc<Self>) {
        let on_complete = |result: TaskResult<Result<()>>| async move {
            if let TaskResult::Completed(Err(err)) = result {
                error!("Accept loop stopped: {err}");
            }
        };

        let selfc = self.clone();
        // Spawns a new task for each new incoming connection
        self.task_group.spawn(
            async move {
                loop {
                    match selfc.listener.accept().await {
                        Ok(conn) => {
                            if let Err(err) = selfc.handle_conn(conn).await {
                                error!("Failed to handle a new conn: {err}")
                            }
                        }
                        Err(err) => {
                            error!("Failed to accept a new conn: {err}")
                        }
                    }
                }
            },
            on_complete,
        );
    }

    /// Shuts down the RPC server
    pub async fn shutdown(&self) {
        self.task_group.cancel().await;
    }

    /// Handles a new connection
    async fn handle_conn(self: &Arc<Self>, conn: Conn<serde_json::Value>) -> Result<()> {
        let endpoint = conn.peer_endpoint().expect("get peer endpoint");
        debug!("Handle a new connection {endpoint}");

        let conn = Arc::new(conn);

        let (ch_tx, ch_rx) = async_channel::unbounded();
        // Create a new connection channel for managing subscriptions
        let channel = Channel::new(ch_tx);

        // Create a response queue
        let queue = ResponseQueue::new();

        let chan = channel.clone();
        let on_complete = |result: TaskResult<Result<()>>| async move {
            if let TaskResult::Completed(Err(err)) = result {
                debug!("Notification loop stopped: {err}");
            }
            // Close the connection subscription channel
            chan.close();
        };

        let conn_cloned = conn.clone();
        let queue_cloned = queue.clone();
        // Start listening for responses in the queue or new notifications
        self.task_group.spawn(
            async move {
                loop {
                    // The select function will prioritize the first future if both futures are ready.
                    // This gives priority to the responses in the response queue.
                    match select(queue_cloned.recv(), ch_rx.recv()).await {
                        Either::Left(res) => {
                            conn_cloned.send(res).await?;
                        }
                        Either::Right(notification) => {
                            let nt = notification?;
                            let params = Some(serde_json::json!(message::NotificationResult {
                                subscription: nt.sub_id,
                                result: Some(nt.result),
                            }));
                            let notification = message::Notification {
                                jsonrpc: message::JSONRPC_VERSION.to_string(),
                                method: nt.method,
                                params,
                            };
                            // debug!("--> {notification}");
                            conn_cloned.send(serde_json::json!(notification)).await?;
                        }
                    }
                }
            },
            on_complete,
        );

        let chan = channel.clone();
        let on_complete = |result: TaskResult<Result<()>>| async move {
            if let TaskResult::Completed(Err(err)) = result {
                error!("Connection {} dropped: {}", endpoint, err);
            } else {
                warn!("Connection {} dropped", endpoint);
            }
            // Close the subscription channel when the connection dropped
            chan.close();
        };

        let selfc = self.clone();
        // Spawn a new task and wait for requests.
        self.task_group.spawn(
            async move {
                loop {
                    let msg = conn.recv().await?;
                    selfc.new_request(queue.clone(), channel.clone(), msg).await;
                }
            },
            on_complete,
        );

        Ok(())
    }

    fn sanity_check(&self, request: serde_json::Value) -> SanityCheckResult {
        let rpc_msg = match serde_json::from_value::<message::Request>(request) {
            Ok(m) => m,
            Err(_) => {
                let response = message::Response {
                    error: Some(message::Error {
                        code: message::PARSE_ERROR_CODE,
                        message: FAILED_TO_PARSE_ERROR_MSG.to_string(),
                        data: None,
                    }),
                    ..Default::default()
                };
                return SanityCheckResult::ErrRes(response);
            }
        };

        if rpc_msg.jsonrpc != message::JSONRPC_VERSION {
            let response = message::Response {
                error: Some(message::Error {
                    code: message::INVALID_REQUEST_ERROR_CODE,
                    message: UNSUPPORTED_JSONRPC_VERSION.to_string(),
                    data: None,
                }),
                id: Some(rpc_msg.id),
                ..Default::default()
            };
            return SanityCheckResult::ErrRes(response);
        }

        debug!("<-- {rpc_msg}");

        // Parse the service name and its method
        let srvc_method_str = rpc_msg.method.clone();
        let srvc_method: Vec<&str> = srvc_method_str.split('.').collect();
        if srvc_method.len() < 2 {
            let response = message::Response {
                error: Some(message::Error {
                    code: message::INVALID_REQUEST_ERROR_CODE,
                    message: INVALID_REQUEST_ERROR_MSG.to_string(),
                    data: None,
                }),
                id: Some(rpc_msg.id),
                ..Default::default()
            };
            return SanityCheckResult::ErrRes(response);
        }

        let srvc_name = srvc_method[0].to_string();
        let method_name = srvc_method[1].to_string();

        SanityCheckResult::NewReq(NewRequest {
            srvc_name,
            method_name,
            msg: rpc_msg,
        })
    }

    /// Spawns a new task for handling the new request
    async fn new_request(
        self: &Arc<Self>,
        queue: Arc<ResponseQueue<serde_json::Value>>,
        channel: Arc<Channel>,
        msg: serde_json::Value,
    ) {
        trace!("--> new request {msg}");
        let on_complete = |result: TaskResult<Result<()>>| async move {
            if let TaskResult::Completed(Err(err)) = result {
                error!("Failed to handle a request: {err}");
            }
        };
        let selfc = self.clone();
        // Spawns a new task for handling the new request, and push the
        // response to the response queue.
        self.task_group.spawn(
            async move {
                let response = selfc.handle_request(channel, msg).await;
                debug!("--> {response}");
                queue.push(serde_json::json!(response)).await;
                Ok(())
            },
            on_complete,
        );
    }

    /// Handles the new request, and returns an RPC Response that has either
    /// an error or result
    async fn handle_request(
        &self,
        channel: Arc<Channel>,
        msg: serde_json::Value,
    ) -> message::Response {
        let req = match self.sanity_check(msg) {
            SanityCheckResult::NewReq(req) => req,
            SanityCheckResult::ErrRes(res) => return res,
        };

        let mut response = message::Response {
            error: None,
            result: None,
            id: Some(req.msg.id.clone()),
            ..Default::default()
        };

        // Check if the service exists in pubsub services list
        if let Some(service) = self.pubsub_services.get(&req.srvc_name) {
            // Check if the method exists within the service
            if let Some(method) = service.get_pubsub_method(&req.method_name) {
                let name = format!("{}.{}", service.name(), req.method_name);
                let params = req.msg.params.unwrap_or(serde_json::json!(()));
                response.result = match method(channel, name, params).await {
                    Ok(res) => Some(res),
                    Err(err) => return err.to_response(Some(req.msg.id), None),
                };

                return response;
            }
        }

        // Check if the service exists in services list
        if let Some(service) = self.services.get(&req.srvc_name) {
            // Check if the method exists within the service
            if let Some(method) = service.get_method(&req.method_name) {
                let params = req.msg.params.unwrap_or(serde_json::json!(()));
                response.result = match method(params).await {
                    Ok(res) => Some(res),
                    Err(err) => return err.to_response(Some(req.msg.id), None),
                };

                return response;
            }
        }

        response.error = Some(message::Error {
            code: message::METHOD_NOT_FOUND_ERROR_CODE,
            message: METHOD_NOT_FOUND_ERROR_MSG.to_string(),
            data: None,
        });

        response
    }
}